Continental C125/C145/O-300 Cylinders/Valves

From: Geoff Newcombe (
I would like to discuss a problem I am having. My Swift has an 0300D with about 185 hours since major. I am experiencing quite a bit of trouble with valve sticking. I have added a quart of Marvel Mystery Oil to the crankcase and also 4 oz. per 10 gallons of av-gas (I don't use auto gas), this has helped some but has not eliminated the problem. It has only occurred on climbout (at about 1500 to 2000 ft. agl), so far, and I have always been able to clear it up by lowering the nose and reducing power to a normal cruise setting. I am concerned that it will happen on takeoff sometime or that I will not be able to clear it up by reducing power and lowering the nose.

I have been told that the only way to cure the problem is to ream the carbon from the valve guides. Any other suggestions before going to that length? I have also been told that this is a common problem with the 0300's although I have never heard of it before, nor did I ever have a problem with a C125 powered Swift I owned back in the late 70's. Maybe I should consider using 50/50 avgas/cargas. Thanks very much for any input you might have for me. Regards,  Geoff Newcombe, Swift 3283K, VeroBeach, FL.

I'm afraid the only "right" way to fix the problem is to remove the cylinders and ream the valve guides, if they are in fact, too tight. Actually, I've seen valves stick in worn out guides also. The guide and valve stem get a build up of carbon, and the carbon on carbon eventually sticks. But usually, the scenario is that the guides are shunk into place at overhaul, and some hours later, the guides get a little smaller with the heating/cooling cycles of the engine. Then, they require reaming. I have removed the valve keepers, dropped the valve into the cylinder, and reamed the guide in place, but I think this is more work than "doing it right".

Do you get strictly 100LL down there? That might work from an octane standpoint, but you would still be subject to the fact there might be alcohol or other additives in the mogas. Before you pull the cylinders, maybe you could use the "rope trick". With rope stuffed in the cylinder to hold the valve up, remove the valve keepers and valve springs. Does the valve drag in the guide? Or wobble? If its tight, you can spin it with a drill motor, lubing the valve stem with Marvel Mystery Oil. If you can get it to "feel right" you might try that for a while. Use MMO in the gas.  If the valve wobbles, the guide is worn out.  -- Jim

Geoff Newcombe ( writes:
Jim - I have had the valve guides done. The exhaust valves were all binding to some extent when we checked them. We used the rope in the cylinder method and had the job done in one morning. After dropping the valves in the cylinder, the buildup of carbon was obvious and two of them were quite tight even with the engine stone cold. The intake valves all worked freely and we did not do them although we did check them all. The engine runs beautifully, so far no more scares on climbout.


From: Steve Wilson (
Subject: O-300 Info
Denis...Last month I saw the following post on the Internet newsgroups (rec.aviation.owning). I talked to Monty (sorry I don't have those e-mails and then answered her after BOTH of us hit on the same fix (great minds think alike, no?). There were other posts with various suggestions. You can see her most recent post and see that low and behold our suggestion worked. Amazing! I am sending this to you because there are so many "C" and "O-300" series engines in Swifts, Jim and I thought it might be helpful to someone with similar symptoms...
My husband and I have a 1962 Cessna 172 that has been acting up for almost a year. It started just before I completed my flight training and has gradually worsened until it is no longer safe to fly. The first time it acted up was with me. The plane shuddered slightly. My rpms may have dropped slightly or my throttle could have slipped. Anyway, I thought it was carburetor ice. Carb heat seemed to help, so I went on my merry way. However, the problem seemed to start showing up at least once every flight. We began to notice that when it happened we would ALWAYS be in the 2200-2400 RPM range. We cleaned the plugs. It seemed to help. We had put in the one piece venturi as required by the A.D. and thought maybe we needed the new nozzle. So we put that in. No change.

I flew it still because the problem didn't seem to be serious. No loss of power, no rpm drops and it happened intermittently. Just a shuddering of the engine. Pull the power pass 2200 or above 2400, and it quit. Then one day it happened on climb out. That really got my attention. I was about 400 ft. agl. At climb out I'm in that rpm range. I pushed the nose down, the rpms went up and it stopped. The airplane went to the mechanic's shop where it was kept for three weeks and flown by the mechanics (two of them). I got a new wiring harness and new intake hoses. It was checked for intake leaks, fuel restrictions, mags, really everything. Compression is good, all in the 70s. New valve cover gaskets. None of this worked. The two mechanics scratched their heads. It may be a mysterious carburetor problem or a sticking valve. $1200 later, it was not fixed.

Now months later and another mechanic, it is really bad. On climb out it drops 200-300 rpms, shudders bad, and it does not want to recover if you drop the nose. We bought a new carburetor and that did not fix it. It has this problem in straight and level if you pull the throttle back to 2400 to 2200, but it is much worse when we are climbing out. Strangely, it never does it on the ground or just after takeoff until we have about 300 to 400 feet. We are baffled, and quite frankly, we do not have a pot full of money to keep searching. Most of the opinions we gotten think a sticking valve would show up on the ground.  Also, when this shuddering happens we have checked the mags, pulled carb heat and leaned it. Sometimes carb heat helps, sometimes leaning helps. The mags are always good.

So guys, I am asking for some serious discussion. This has baffled multiple mechanics and ourselves. Help point us in the right direction before I take my gun out to that airplane and shoot it!  Thanks, Debbie and Henry McFarland
(Steve Wilson's Reply...)
Probably the least expensive thing to try is a new set of valve springs. I've heard of this problem and know the new springs did the trick in that case. If you figure it out, would you please post answer here? Thanks...Steve Wilson DPA & 0TX1 Swift N77753 (flying) Swift N3876K (restoring)
Subject: Continental 0-300D Problems Solved
From: Henry and Debbie McFarland <>
Date: 01/06/99 8:27 AM Central Standard Time
To the guys who responded to my cry for help for my 0-300D Continental problems back in December, I would like to thank you. A new set of valve springs from Fresno for $67 fixed the problem. I have flown it about 5 hours and everything seems fine. It sounds stronger, and I have been indicating 125 mph! I could only get 120 on a cool day before the new springs. I guess we didn't replace them before they were needed ;). However, the new carburetor that we bought is set too rich. I have to lean the airplane on the ground. ARGH! Flying can be such a pain. Ahh...but the joys. Thanks again, Debbie McFarland Luscombe 8A (his) Cessna 172C (hers) Cessna 195B, project (ours)

O-300 VALVE COVER GASKETS...  (010100)
Subj: O-300 Question
From: Michelle Dolin <>
Happy New Year from North Carolina. My question is about our O-300A in our Swift. The valve covers appeared to be leaking on the #1 & #3 cylinders. We replaced the all the gaskets with the continental black fiber type. We flew the plane, came back still leaking. We checked the cover bolts...flew it again still leaked. We then went with the silicone gasket...same process still leaked. We then replaced the valve covers themselves...still leaking. All the patterns in the cowling lead the IA to believe its coming from the valve covers. If it was coming from the pushrod tubes he reasoned, the oil would be running down towards the case...but its not. He finds it hard to believe that both cylinders could be warped. They show no indication. Do you have any suggestions?  Michelle

The problem is probably the cylinders were not completely clean when the covers were first installed. The cylinders cannot warp to such a degree that the covers leak. The silicone gaskets usually solve this problem. My suggestion is to remove the covers and gaskets, clean the surfaces thoroughly, then decide whether to use the original type gaskets or the silicone. The covers must be reasonably straight. If you use the silicone gaskets follow the manufacturers instructions. If you use the original type gaskets, the manual calls for "a non-hardening gasket paste". (Tite-Seal) Tite-Seal came out in about 1920 and there are many more modern sealants which will do a better job. Some make it very hard to remove the cover next time. But hey, if you do it right, the cover should not have to come off until the next overhaul, right? Don't use RTV silicone unless the label clearly says "oil resistant". While you have the covers off, beg, borrow, buy, or steal an expander tool and tighten up the push rod tubes. El Reno in OK sells them. Happy New Year!  --  Jim

From: Wesley & Susan Knettle <>
For Michelles O-300 Valve cover leaks. I gather from her 1st Jan post that gaskets were replaced untill she ended up with the silicon rubber ones. Still leaked. Then new covers and still leaked. She should probably look for a crack either in the face area the cover bolts too or the area surrounding the outboard end of each pushrod tube housing. Sometimes folks get carried away with the ball swedging tool. A crack there may squirt towards the outboard direction. Some words of caution on the silicon rubber gasket usage. All surfaces must be VERY Dry and Clean / Torque figure for your cover screws drops way down to 5 to 15 inch pounds and as always your mechanic should re-dimple the cover's bolt holes outward.

From: George McClellan <>
If the cover leaks continue after following the good advice to make sure the surfaces are clean and that the covers are flat, that is that the screws haven't been over tightened and distorted the sealing surface, you should check that the engine vent line is clear of any obstruction which can cause high engine case pressure. -- George McClellan

From: "Allen E. Andersen" <>
Subject: January #1 GTS Internet Update
Interesting story about the valve cover gaskets leaking so badly on the O-300 cylinders. I have come across similar problems many times on those cylinders, and virtually all of them were leaking around the pushrod tubes as they enter the top of the cylinder. They always look like the valve cover gasket is leaking, but not so. If you understand that the pushrod tube is a metal to metal seal as it enters the cylinder head, you'll also understand that if you , or another mechanic picks up those same cylinders by the pushrod tubes while they are off of the airplane, it WILL cause them to leak. There are several tools out there which will re- swedge the tubes in the cylinder on the airplane. It requires that the rocker arms be removed and the pushrods too, but it will fit into the pushrod tube from the rocker arm side of the cylinder after the valve cover and the other stuff is removed. Several expanding ball bearings will expand the tube from the inside and reseal the pushrod housing which will then not leak until the next mechanic picks the cylinder up by the tubes again. The tool costs around $50 and it will probably cost another $50 to have a knowledgeable mechanic do it for you. Good luck. Al

100 OCTANE VALVES... (010600)
Subject: Re: More Monty stuff !
From: Pete King <>
Hi, Jim,
What is the difference between the 125 valves and the 100 0ctane valves ?

The old 1940's valves for both the 125 and 145 are p/n 3920 and 3921. The first generation of so-called 100 octane valves are p/n 629404 and 531608. There are several newer p/n's, including a 30 degree intake valve, p/n 7641792. My TCM cylinders have something newer than that yet, which I'm not familiar with. The Superior Millennium cylinders use a chrome plated exhaust valve and a special valve guide. The difference? The 100 octane valves are a more exotic steel and stand up to higher temperatures. The old 3920/3921 valves lap in better and never suffer from leakage until overtemped. I had an O-300 with 3920 intake valves and 629404 exhaust valves that went over 2000 hours. -- Jim

Subject: Re: O-300 question again
From: Michelle Dolin <>
I asked you a few weeks ago about an oil leak on an O-300. It appeared to be leaking around the #1,3&2 valve covers. You had suggested that the pushrod tubes were loose. My question now is, can they be tightened without taking the cylinders off?

Sure, I thought I had explained that. You need to pull off the rocker covers, the rocker arms, and the pushrods. Then with the tool which I described last time, you expand the upper (outer) end of the pushrod tube where it goes into the aluminum casting at the cylinder head. A couple of cautions -- if it is an early C-145 or an O- 300 that someone has assembled without circlips holding the lifter together you can pull the cup apart from the lifter when you pull out the pushrod. If the cup falls out of place don't rotate the engine! If its just out of place you might have to pull a cylinder, but if you break a lifter, you have to split the case to replace it. Don't expand the pushrod tube too much and crack the cylinder. To slide the rocker shafts out on #3 and #4 cylinders (the center ones) is a little tricky, but it can be done. You might have to loosen the cylinder base nuts on the adjacent cylinders and move the cylinder around a little.  --  Jim

TAKE A SEAT... (3200)
Subject: Re: Engine C-145 Steel Cylinders
From: Jerry Swartz <>
Jim: Did do the borescope thing. No carbon deposits. Mechanic feels we should just run it. Looks to him as if the exhaust valve in question has not seated yet. (13 hrs since top)??? Don't understand your clearance statement. How does a longer push rod affect the seating of the valve?? I don't profess to being a mechanic , so please bare with me when I ask dumb questions. Another question: AD 64-05-06. It would appear to me that my mount legs have at one time or another been drilled at the top and bottom and what looks like a rivet installed in the holes. I can't believe that these rivets are being removed and re-installed at each annual, to check the tube for water and rust. The heads of these rivets look as if they have not been touched for years. Am I missing something in my interpretation of this AD??? Jerry Swartz

Jerry: Just running it might work, the minimum is 80/60. However, exhaust valve leakage is actually not permissible. Borescoping does not show much, if anything, re: the valves. The reason I suggested you check the rocker clearance, is these engines have hydraulic lifters and after they have run a while the rocker clearance should be "0". If they have some clearance the valve may leak. When the engine is set up, new or at overhaul, the clearance should be .030 to .110. After the lifter "pumps up" the clearance should be "0". Exhaust valves don't usually "seat". The rocker arms are not adjustable, so the only way to change the cold clearance to is to grand the valve, valve seat, valve stem, rocker arm or valve stem, or to install a longer AD 64-05-06, it sounds like you have a Univair replacement mount instead of a 54 year old Globe or Temco made mount. Of course, even the Univair mount is probably 30 years old by now. The Univair mounts had those little drive rivets. Even so, whoever has been annualing your airplane has not been inspecting the mount properly. Read the AD note. Those rivets are supposed to be replaced by removable screws to permit annual flushing with oil. Call me if you have further questions. -- Jim

Subject: Re: Engine 77759
From: Jerry Swartz <>
Steve: Started the annual and found a cracked cylinder. Purchased a complete new assembly (Continental) and in the process of having it installed. Have since picked up some conversation from the "know it alls" that I should have opted for a milleneum cylinder, and/or better yet, replaced the rest of the five with milleneum. Also hearing that there have been problems with Continental Cylinders etc. etc. Please give me your ideas on the Cylinder question for 145's and larger Continentals. I have no idea what these people are talking about, and my mechanic isn't saying a word. -- Jerry S.

Well Jerry, Opinions are like a**h***s. Everyone has one! I also find their value to the recipient is generally proportional to their cost. Mine's free, so beware! It is nice to have a complete set of new cylinders regardless of who actually made them. Both the Superior and TCM cylinders have had their share of problems. I like the idea Superior has with taper, extra fins, et alas, but the TCM cyls were good for the first 50 or so years, so hard to say which is really best. You know if you have problems the ones you have are sh**, and if they really work out great, you wouldn't own anything else! The problem is they cost BIG bucks and it is a tough decision. I would look at the overall health of the engine. If it is high time and you are trying to get a few more hours out of it, then maybe replacing one cyl at a time is OK (I probably wouldn't do it, but it is OK). If the engine is basically new, I would surely consider just one cylinder. In any event, I would not mix cylinders chrome Vs steel, or manufacturers. OTOH, If the cylinders have something over 600 hours and/or are over 10 years since O/H, I would probably replace the entire set. My belief is that O-300 series engines have 1,000 hour cylinders. I really cannot speak for Superior cyls, but TCM cyls need topped at least every 1,000 hours. I don't care what you do with them, that's about when they wear out (sooner if they sit around more than fly)! The bottom end will go 1,800 to 2,000 hours or more. The bottom end is nearly bulletproof, but the cylinders are not as tough.

I don't know if I have helped you are not. Maybe confused you more. My apologies!. Personally I really like the O-300 engines! In fact, I don't allow anything else in my shop (unless the customer is paying big bucks, then he can bring anything in he wants, LOL). I think sticking to one engine makes life easier and hey, it is basically a good engine! It is inevitably your money! You have to make the decision on how to spend it. Sometimes is it better to just bite the bullet and spend the money now. Other times a little repair goes a long way. I guess I have said all this to say, you listen to all the B/S and make up your own mind. It's you airplane; it's your money; and maybe most important, it's your butt hanging on that engine! Good luck! ... Steve W

Subject: Re: C-145
From: Jerry Swartz <>
Steve: Thanks for your response to my cylinder replacement question. My engine is a C-145-2H with 426 hrs. SMOH, which was in 1971, and 21 hrs since TOP which was done in 1991. Engine and airframe both have about 1700 hrs. TT. According to the logs the #5 cylinder has been the biggest problem thru the years having been replaced twice and overhauled twice. The cylinder I replaced was # 4 and had a crack emitting from the spark plug brass fitting. Compression's on the rest of the cylinders are 70 plus, except for # 1 which evidently has an exhaust valve leaking. Jim has given me some input on that question, although my mechanic is still saying RUN IT!!!!, so who knows. Thanks again for your input. Jerry S.

If your engine has only accumulated 21 hours since a TOH in 1991, I would recommend all the cylinders be either overhauled or replaced (at a minimum they should be removed and inspected for conformity to specs). As one example: The valve springs won't keep their tension that many years. Unfortunately, what you are experiencing is the beginning of the end for all the cylinders; one is questionable, one is cracked, and one is leaking. I'm certain Monty would agree if you have an exhaust valve leaking it should be taken care of prior to further flight! Maybe just staking the valve will take care of it, but be careful! Hang in there and enjoy the privilege of aircraft ownership.... Steve W

HOW DRY I AM... (3300)
Subj: Leaking Exhaust Valves
Monty, On the subject of leaking exhaust valves, I have found that many times, it is not too much clearance between valve tip and rocker that cause the problems, but lack of proper dry clearance, which becomes very hard to measure after assembly, and running of the engine. You will never know if those darn little lifter bodies are completely bled down unless they are removed completely, which generally requires cylinder removal, especially if the tiny snap rings are present. But, when encountering a leaky valve, there is one way to give you an idea if the dry clearance is not sufficient. If after checking to see that there is 0 clearance between the valve tip and rocker, (lifter body pumped up) simply remove the rocker arm and then re-pressurize cylinder. If leak stops, or reduces significantly, cause is most likely inadequate dry clearance. This is common, especially on higher time cylinders due to multiple valve and valve seat grindings which reduce the clearance. You will need to start from the beginning: remove hydraulic lifter body, completely bleed down, reassemble, and check dry clearance to see if the assumption is correct, and how much you will need to grind off the rocker face if so. This is the only way to increase clearance, as I believe, if memory serves me correct, that Continental doesn't make different length pushrods for this engine. Most automotive engine shops have a rocker arm grinder to do this.

If after initially removing the rocker arm, and rechecking for leaks, the leak still persists, stake the valve with a leather or rubber mallet a few times with cylinder pressurized, be careful not to hit it at an angle, or too hard as you will have the piston at top-dead-center, and don't want to hit it with the valve; just enough to reset the valve. If leak goes away, it may have been debris under between valve and seat, or may possibly indicate a worn valve guide, and staking it may have just allowed it to change position slightly enough to seal better. I would then reassemble, run engine, and recheck. If leaking again, then go the route of removing lifter and checking dry clearance. If the leakage does not stop, the problem could still be inadequate dry clearance, but due to the valve being held open because of this, and the subsequent leakage, if the engine has been run this way for any significant amount of time, there could be valve/valve seat damage that can only be repaired by regrinding or replacement. Let me know your thoughts Monty. I love listening to all your advice. -- Marc Dart

10-4 on most every thing you say. Certainly if the valve is not closing completely it will leak. What I was getting at, and may not have articulated it well, is if the valve "hammers" the seat too hard, it will eventually leak. The C-75, 85, 90, 125, 145, O-200 and O-300 series engines have P.030 pushrods available in the parts catalogue. I have seen aftermarket pushrods up to P.070, but I'm not sure those are genuine. -- Jim

From: Gene Gillott <>
Subject: 0-300 exhaust valves
Just thought that I would add my 2-bits worth to the discussions on 0-300 exhaust valves. For a number of years I had persistent problems with exhaust valve leaks. Would get around 50 hours between cylinder pulls - always the same jug (left rear). The engine shop bent over backwards trying to figure out what the problem was; tried different seat angles, guides etc. I finally took a good look at the baffles, cowing. All were as tight as I could make them. Then I just had a good look in through the grill to see what was different from one side and the other. It turns out that the heater hose was running under the base of this cylinder. I moved it to one side and got an immediate decrease of 50 Deg of cylinder head temp. Turns out that was the answer. I had always found that the temps were nudging the high side - not over redline but getting close. I guess prolonged high temps just killed the valve. That was quite a few years ago and I have not had a bad valve since. The moral is: "watch the temperatures". -- Gene Gillott, C-FKXY

Subj: Valves for C-145-2
From: Bud England <>
Jim: Talk to me a minute about valves. I'll be starting the overhaul of my 145 soon. I have valve P/N's 3920 & 3921 as original parts, with 62904 (bad #?) & 531608 as the later #'s. Presumably the new #'s are larger valves rated at higher temp's and pressures. If so, do they only require different seat insert or is machining required? I also have a note about a 30 degree intake valve, P/N 7641792. What are the pros and cons of this change - and I also have the same question regarding if any head machining is required for different inserts. I'm presuming that the guides are the same for all. Thnx, Bud

Bud, The 629404 exhaust valves will work fine on the original seats, which are steel. The 30 degree intake valves will need new steel seats which are physically bigger. The 30 degree intake valves are generally considered better and came about in the '70's when the majority of training airplanes were Cessna 150's and they were having a rash of valve and cylinder trouble. Part of the "fix" was to retard the timing to 24 degrees. (which I always thought was a dumb idea) and the other part were the 30 degree intake valves. I'm not familiar with p/n 7641792. All the guides to my knowledge are the same. Superior there in Dallas sells a PMA valve that takes a special guide.  The old 3920 and 3921 valves used to work just fine, but they can't take heat like the newer p/n's.  At my last overhaul, I sold my old cylinders and bought new ones. If you can buy new for $600 ea. you can't afford to screw around changing guides, seats and valves. It will cost $400 -- $500 for each cylinder and you still have a 40 year old part. -- Jim

From: Bud England <>
Jim:  Would you mind repeating the P/N's for the latest valves and seats for the 145? I thought I had printed it but if so, I can't find it.

The early valves and seats were a 4 digit number - 3920 for the intake valve and 3921 for the exhaust valve. And 3912 for the intake seat and 3923 for the exhaust seat. The first so called 100 octane intake valves were 45 degree valves, p/n 531608. For a long time, the 629404 was the "standard" 100 octane exhaust valve. In the late '70's a 30 degree intake valve came out, p/n 641792. I don't know the absolute latest p/n's. In my new cylinders the exhaust valve is p/n 654064. Caution - some of these newer valves require a special matching guide. Superior down there in TX also has a very good exhaust valve which is chrome plated I believe. It requires a special guide that they will sell you. Having said that, what I really like to do is buy all new cylinders which will include all new valves and guides and seats. I think the Superior Millennium Cylinders are "superior" to the TCM's. Also a little more expensive, $700 and some compared to $600. You might try warming that rubber in a warm liquid soap solution. -- Jim

Subj: cylinders
From: Jerry Swartz <>
Jim: Just got done reading the newsletter, and noted your comments to Bud England. You stated that you feel the Superior Millennium Cylinders are superior to the TCM's, even tho they cost more. When I talked to you about buying the TCM's for my engine last year, I was under the impression that you didn't think the Superior's were worth the additional cost? So far so good with mine, but I only have about ten hours on them. Is there something now that I should be looking for, and/or worrying about??? Jerry Swartz N77759

I have the TCM cylinders also. After I bought mine they published CSB98-1B, in which they admitted sending out some defective valves. Now they are having reports of premature valve wear due to the assembly method. They are supposed to be covered under warranty, but I guess you've got to kick and scream sometimes to get TCM to pick up the tab. I have at least 3 friends with the TCM cylinders who had to have them removed and repaired in the last year. I would hope TCM has fixed the problem. I have my fingers crossed on my cylinders too -- I only have a little more than 10 hours on them also. The cylinders need to have 150 hours on them to check per CSB98-1B, but none of my friends got much over 50 hours on them before the valves were leaking badly. If I have a problem I have already talked to a shop that is familiar with the TCM warranty process. I wouldn't worry. The cylinders don't fail catastrophically, the valves just start leaking over time. It is a disappointment to pull "almost new" cylinders, but hopefully we won't have to. -- Jim

(Editor says... For what it's worth, I had my O-300 overhauled in 1995 and I went with new Superior Millennium cylinders. Thus far, 500+ hours later, no problems.)

From: Marvin Homsley <>
Jim, as usual I need your advice. I discovered today that my cylinders are junk. Three are cracked and three are worn beyond service limits, but they could be saved by chroming. I have decided to put on all new Millenium cylinders from Superior Air Parts. This has completely wrecked my budget for this overhaul. Therefore I am trying to save some money somewhere else and that is in the engine bottom end. I have got prices from two places on doing everything necessary to the bottom end once I send them the pieces. It seems like there is a LOT of labor involved that I might be able to do myself on this bottom end. I think I should have the camshaft reground just on general principals. That means that the hydraulic lifters must be resurfaced also. I do not have any equipment to do those two things so I will send them out. I can get all my magnaflux checks done locally (by and aircraft shop) for free. We are trading favors here. I believe I can save a lot of labor money with the crankshaft counterweight bushings, the connecting rod bushings, and the rocker arm bushings. I would like to put in those bushings myself. We are talking about something that seems relatively simple. Just press out the old bushing and press in a new one. Have you ever done this before ? If you have done it, do you have any favorite place to buy the bushings. Marvin Homsley N80740

The TCM cylinders are about $100 ea. cheaper than the Milleniums. I have the TCM's and they have had problems with quality control. Hopefully, that is over now. The best (cheapest) place for the TCM cylinders has been Mattituck - they advertise in Sport Aviation. The counterweight pins and bushings are not a mandatory change on the O-300. The bigger TCM engines have a service bulletin to change them at overhaul, but the O-300 manual says to inspect and replace as necessary. At 1200 hours perhaps your pins and bushings do not need replacing. Then again, if they were not changed at the last overhaul, they might. I have changed the bushings. They need to be miked carefully and pressed in about .001 tight. (read the manual) I get most of my parts from Superior. I get my cam and lifters reground by Aircraft Specialties in Tulsa, OK. With new cylinders you don't have to do anything with the upper end - no rocker bushings etc. Some shops replace all the hydraulic units in the lifters. That may be a good idea, but you can check yours first by filling them with gas or solvent and attempting to push the two parts back together. They should not allow you to do this until the check ball is displaced with a piece of .040 brass safety wire inserted in the plunger. This accomplishes two things, it "bleeds Down" the lifter and checks it for hydraulic function. This is necessary because after the engine is assembled you will need to check the valve lash at .030 to .110and you can't to do that you need all the oil flushed out of the lifters.It's pretty hard telling how to overhaul an engine by email! But if there are further questions - write back! -- Jim