Sherman GAA help needed

[WillWagner]

We have a nice Sherman at the Museum. It has a single issue, it smokes like a freight train at first start, oil smoke. The compression is OK, leakdown is nothing. After running maybe 15 mins under a load of just the weight of itself, the smoke will clear and there is no smoke on acel or decel. It will start right up with no smoke after sitting 5, 10, 15 mins, but, if you let it it sit over night, it fills the compound with smoke. Again, it clears after running. It is worse after an oil change.

If it were a car, i'd say valve seals, but, none on the GAA. I do know that there are little holes in the cups on top of the retainers/springs. My Q is, is it possible to have the holes plug and let the oil, when it is hot, overflow the cups and run down the valve stems causing this issue?

If anyone has experience on the GAA and can give me a hand, PM me and I will send you a number so we can chat about this big 'ol V8.

Will

 

[gimpyrobb]

Wow Will, you knew it was coming...

 

[armytruck63]

Is the crankcase building up pressure somehow either when running or after shutdown?

 

[WillWagner]

No CC pressure, the vent is open. Never been inside one of these, done a quite a bit of reading. I want to see inside or see parts so I have an idea of what is inside that keeps the oil from sucking down the guides while running. I think this feature is malfunctioning and causing the issue it is supposed to prevent.

 

[Jeepsinker]

Most engines with no valve seals incorporated into the design use the clearance fit of the valve guide itself to keep the oil out. Sounds like the valve guides are worn and they are expanding when they warm up. You can see about having the guides knurled, or just have them replaced. Either way the heads had to come off. Not many places do valve guide knurling anymore.

 

[steelypip]

Yes, I'd guess it's leakdown past guides as well. A better question, though, is why there's so much oil in the cam boxes after shutdown - is there a problem with the drainback holes? Are you sure the crankcase isn't pressurizing when the engine is running?

 

[Jeepsinker]

Could be sludge buildup. In fact it is quite likely if it an old build and ran the older generations of oil in it. I've pulled valve covers where you couldn't even see the rocker arms for all the sludge.

 

[WillWagner]

Could be sludge buildup. In fact it is quite likely if it an old build and ran the older generations of oil in it. I've pulled valve covers where you couldn't even see the rocker arms for all the sludge.

This is what I would like to have verified. There is no CC pressure out the breather when running with the tank as a load. I have not put a manometer on it, but I can tell there is nothing major. In my past experience, valve guides with excessive clearance tend to suck oil down them on decel and, if worn heavily, they will cause high cc pressure loaded. On this engine, the oil control is from some holes in the retainer. the keepers are down inside this "cup" if you will, that is the retainer. From what I have read and seen in the TM for this engine, there is a bleed hole that looks like it shunts the oil the cam sheds onto the valve stem/retainer and directs it away from the stem/guide. If that hole plugs from sludge or whatever, is it possible to have enough oil migrate down the guide if a valve is open and give the cylinder a giant amt of oil? Another symptom is that oil slobbers from different cylinders AFTER it sits. Ex, one time, 1 and 4 on left bank and 1 and 4 rt bank will slobber real bad, after running loaded, they will dry up. park it, let it sit a day or so, fire it, 2 and 4 lb, 1 and 3 rt bank slobber. I can't figure it out for the life of me!

 

[Jeepsinker]

Time to put a Mk-1 eyeball on some internals. Or you could drain the oil, add a few quarts of transmission fluid and then fill the rest with fresh oil, run it around for a while, let it sit for a couple days, run it around for another couple hours, then drain and refill with fresh oil again and see how it does.

 

[steelypip]

I wouldn't do a flush-and-pray if you can avoid it. GAAs aren't all that rare, but they're not free or current production, either. You're taking a risk if you do a detergent flush on an engine - you can trash bearings either through insufficient lubricity or because the detergent broke a bunch of abrasive crud loose and it was pumped into the bearings.

Much better to put an eyeball on it. Ideally, I'd pull the engine, take the cam covers and oil pan and clean/examine everything. Unfortunately, it doesn't look like you can have the valley cover off without removing the cylinder heads, but should you choose to do so, it would allow a complete examination and gentle cleaning (I prefer 1K kerosene and a brush for delicate stuff) of everything without dismantling the short block.

 

[WillWagner]

Did a flush, 1 gal of diesel and the rest oil, idled for a while to bring the engine up to temp, drained, refilled. The oil was clean the first drain, no chunks, fairl clear, it has been sitting. My first thought was stuck oil control rings, hence the flush. The smoke was no better/worse after the "flush", but the engine really had not been loaded an a while. I do not remember if the engine is an original or a rebuild....guess I need to find that out, most likely a rebuild. I did borescope the cylinders on the ones that were oiling at first, 1 & 4 on both banks, they look good, slight marks from the rings sitting in one place for years. I would prefer NOT to pull this thing! It has been has been out for an episode of Tank Garage, it smoked then. It got a new clutch in that show. Remember, the oil slobber out the manifolds change each run cycle, a cylinder issue would stay in the same cylinder all the time. Thanks all for the ideas, keep 'em coming!

 

[steve6x6x6]

I thought there was a motor oil that would decrease oil consuption. Or even add STP to the motor oil will slow down oil consuption.

 

[Jeepsinker]

Seeing how it is changing cylinders each time it has to be on either the intake or exhaust valve, not both. It is leaking oil through whichever valves are left open when the engine comes to a stop. Since the flush had no effect it looks like you will just have to get a look at the insides. Perhaps someone built it years back and left out a splash shield or something.

 

[eme411]

my 2 cents is look at the valve guides , It's much cheaper to fix what still runs than fix it after you blow the engine, also check that the engine is not one of the German rebuilds, there was a major problem with these , the rods were not torqued , beware , this is not your car , GAA's do not grow on trees and are not cheap,

 

[WillWagner]

An update, decided to pull the lids and see if the holes in the cups are plugged up. Jake and I went down to the Museum last Sat and went to work on it while sitting on the line. Got the lids loose, but the studs are a bit too tall to get the v/c off with the air filters installed. Tried dropping the oil bath, still not enough room. Gotta pull the compartment doors and top plate to remove the air cleaners and then the valve covers

 

[WillWagner]

An update, the guys at the Museum pulled the rear armor, air filters and pulled the lids. Lots of rusty parts up top. The cam lobes are all there, the valve cups are clear but pitted on the cam contact face and I noted some scoring on the valve buckets. The oill drain holes are clear. My best guess is that the valve stems are pitted and the scoring on the buckets is allowing the oil to drain down the valves into the cylinders that have open valves and oil will sit on the closed valves so when the engine starts, the oil that has settled just goes directly into the cylinder...a best guess. I put the lids back on it.

 

[Tow4]

Sounds like a lot of work needed on that engine. I'd look around for another engine that is either rebuilt or one that I can rebuild and then change it out. Since it still runs you are not pressed for time so you can look around and maybe find a good deal. With that in mind, you can probably run that one the way it is for a while. Good luck.

 

[WillWagner]

There is an engine in one of the containers that has new liners in it already and is ready to be assembled. Maybe another project for another day. I can't for the life of me figure out where all the time goes, seems there just isn't enough of it to do what needs to be done in a timely manner. Maybe when I retire.

 

[Jeepsinker]

It doesn't work that way, you have to make time. When you retire you get even more busy.