C-90 gets tight when warm

I have a J3 with a C-90 overhauled in 1995. New crank, std cylinders. It now has 350 hours smoh

First flight of day turns 2450/2475 on take off. Land pull prop through and engine feels tight, fly 2 hours later will only turn 2350 on takeoff and it takes about 1" more throttle to maintain cruise 2300 in cruise. After about 20 minutes of flight throttle position back to normal. Land pull prop through feels tight. Cool over night pull through all feels normal.

Ring clearance checked good, piston clearance good.

Any ideas?

Thanks in advance

These engines all get tight when they are hot. Check a few other engines for comparison right after they shut down. That's a red herring.

-Cub Builder

Does it happen to have a Prestolite starter? jrh

N86250 said:

Does it happen to have a Prestolite starter? jrh

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C90-8 no starter

Mine does it every once in a while.

How tight is tight? If real tight... I'd bet it's the thrust washers. Similar experience happened to a friend with his C90-8. Page 97 and 98 in the C-85 overhaul manual show these washers.

BUT, if it's a new problem, as in it's been run 300 hours with no issue and now the issue, I'd bet the above theory isn't correct. (Opinion)

Sikorsky

Sikorsky said:

How tight is tight? If real tight... I'd bet it's the thrust washers. Similar experience happened to a friend with his C90-8. Page 97 and 98 in the C-85 overhaul manual show these washers.

BUT, if it's a new problem, as in it's been run 300 hours with no issue and now the issue, I'd bet the above theory isn't correct. (Opinion)

Sikorsky

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I have had this problem since overhaul. Not new. Pulling on the prop hub has almost as much end play as when cool

I installed cyl head temp gauge, checked all four cylinders and found temperature variation up to 60 degrees F.

Thrust washers, I'd bet.

Probably not the same issue, but this also happened to my high time 0-320-B2B 160 HP. Started fine when cold, but when it warmed up, it was pretty tight. What it turned out to be was that the case halves were worn enough from galling that they were compressing the main bearings, or one of them, at least. As the case wears, the main bearing oil clearance drops. I bought the engine used, and there were several prior top overhauls. Maybe they didn't split the case and check the mains? This was discovered during the subsequent overhaul. The case had to be machined and rebored.

Sikorsky said:

Thrust washers, I'd bet.

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what he said...

Did you solve the problem. I have identical problem.

I'd check the crankshaft to thrust washer end clearance.TCM SB03-5 says so.

Can the crankshaft end play easily be measured by pulling and pushing the prop (and attached crankshaft) and measuring the distance it moves within its limits.

http://www.tcmlink.com/pdf2/SB03-5.pdf

Gary

The end play measured approximately .007. When hot/warm after flight it still has end play. This tells me it is not the thrust washer causing the problem but most likely the main bearing.

Jim

I’ve seen this before...but none of the rigs had propellers. Carbon build up between the piston rings and the ring grooves was pretty common on old flat heads that ran rich...few fords and chevy small blocks... I didn’t work on many gas pots as I worked as a journeyman diesel mechanic for class 8 dealerships. This one time back in band camp...when leaded gasoline was to be had at the pump.....was the foreman for Diamond Reo... this customer brought in a 64 Chevy one ton with a 396.. it had the problem you describe...the starter barely turned over the engine when it was hot.. starting system check good using an amp shunt and meter to check the run load on the starter...the boss man..Bryce Morris...told me the story and how to fix it. If I tell the story most of you folks will think I’m nutz! Ah...don’t really give a chit...I’ve used this trick many times...but have never done it on an aircraft engine..
Best way to tell the story is to relate one story surrounded by a bunch of guys who thought I was nutz!
About 25 years ago...worked for RA Hanson Inc..as the director of mining and the general manager of the mine here in Platinum Ak. We had terminated both mechanics.. the director of Fabrication Bob Warn came to me requesting I take a look at a fork lift that was stinking up the fab shop and wouldn’t start when it was hot. I told Bob to send someone to Safeway to purchase a one pound bag of white rice... Q: what are you going to do with that? A: Fix your problem. Bob refused. He wasn’t about to tell someone to go get a bag of rice to fix a machine that was running to rich. So I go buy the rice...return to the shop. Q: Do you want us to drag it over to the mechanics shop...A: Nope...it’ll only take a few minutes...I’ll do it right where it is...in the middle of the shop. So...I had a flat blade screw driver, some white paper, piece of fine grit Emory cloth and that bag of rice. Word got around... Don’t recall the number of guys surrounding the fork lift...three fab crews, machine shop crew, burn room crew...
Popped the off the distributor cap...dragged the Emory cloth through the points...eye balled the gap...dug the paper though the points to clean them.
I popped the hose off the up draft carburetor... started the fork lift, eyes stinging from the fumes...adjusted the air fuel mixture and screwed in the idle screw...the engine was missing and sputtering around 2000 rpm... slowly fed that white rice into the carburetor while keeping the engine rpm up with my left hand.. probably let that carburetor suck half that bag of rice into the carb.. had this nice brown cloud of rice smoke. Screwed out the idle screw, fine tuned the mixture. Ran like a smooth sewing machine....Done. Heard more than a few people say...”if I hadn’t seen it with my own eyes, I would have never believed it”. To this day I don’t know how the rice cleans the carbon deposits from the ring grooves...but it does.

Rice. Now I’ll be scratching my head for days.....


Sent from my iPhone using SuperCub.Org

It's abrasive and doesn't burn immediately. It was bead blasting the combustion chambers.

Web

MMO and Soy sauce might make it even work better

;-)

Glenn

Another old school fix for carbon deposits was to dribble water down the carb while it was running. Supposedly the steam expansion helped break up deposits. Seems hard to do on an updraft carb though.

Web

wireweinie said:

Another old school fix for carbon deposits was to dribble water down the carb while it was running. Supposedly the steam expansion helped break up deposits. Seems hard to do on an updraft carb though.

Web

Click to expand...

Pump up garden sprayer work good

Glenn

old cub pilot said:

I have a J3 with a C-90 overhauled in 1995. New crank, std cylinders. It now has 350 hours smoh......

Ring clearance checked good, piston clearance good.

Any ideas?

Thanks in advance

Click to expand...

I guess this means you had the cylinders off to check ring end and side gap clearances? Any signs of scoring or excessive heating? Carbon buildup? I'd be tempted to get it hot, land, remove the top plugs and pull it through against no compression. Feel for change in tightnesss along the four piston strokes (cylinder choke) and listen for squeaks-noise from tight bearing with a wood dowel to ear against the case. A tight bearing should cause higher oil temp issues.

Surely not chrome rings in a chrome cylinder? Had two ask but unlikely.

I've had a fresh overhaul C-90 and C-85 Stroker (C-90 equivalent) and while tighter when hot static the same rpms

Gary

Buddy's c-85 had same symptoms main bearing fit was worn and bearing had slipped.