EA-81 Burned exhaust valve after 12k ?

[airweld]

My son and I rebuilt this motor 12k miles ago with all new bearings, seals, rings, heads rebuilt by local shop, cylinders honed, and new oil pump. EA-81 solids, non-turbo in 84 gl wagon. Started using oil after a few thousand miles, so we found #3 cyl. had an oily plug but the compression tested same as other cylinders. Put in next hotter plug and eventually when the plug fouled, we would replace it with a clean one, and now at 12k, the valve has a big notch burned into it. The valve stem seals of all four exhaust valves were shot with the small springs laying in bottom of pan. I assumed that the oil was getting thru the guides and eventually caused the burned valve. Now I am not so sure. The shop that rebuilt the heads has no clue why the valve seals failed, and I have learned that the exhaust valves did not have stem seals originally. The shop did not know this and put them on because they came in the Felpro kit. They rebuilt the heads again and put the same seals on again. I am wondering now if the bad seals may not have been the cause of the oil in cylinders, because it was up to a quart in 200 miles or worse at the end. I can't see that much oil getting by the guides? There was no indication of cylinder wear when we did the overhaul, so I assumed that a ring and hone job would be fine. The cylinders all look great now, no scratches or anything. Still see hone marks. I really don't want to split the case so can anyone give me any advice on valve guide seals, burned valves, and what to look for? The machine shop says the valve burned due to coolant in the cylinder, but there was no coolant in oil, or vice versa, no coolant smell in exhaust (no white smoke either). The valve had clearance to the rocker arm (did not hold the valve open). The front crank seal was leaking some and we put a speedy sleeve on the pulley and new seal, but still I don't think that accounts for all the oil used. Well if anyone can help, we would like to assemble this engine, but want to be sure we haven't overlooked something. PS. I am an aircraft mechanic, however this is my first suby overhaul. Thanks.

[naru]

Oil consumption from failed oil rings or intake valve guide resulted in detonation and too high temps for the exhaust valve.

 

I`ve burnt a valve w/a vacuum leak too.

 

I would inspect valve to guide clearances.

Oil rings,piston ring groove,piston for cracks and clearance,and the bore too.

[Turbone]

How was the engine broken in?

If its not properly broken in, oil consumption and other problems are possible.

[airweld]

Good question Turbone,

How would I be able to tell by looking at the cylinder walls if the rings were not properly broken in (without splitting case)? I would think that after 12k the rings would be sticking and scoring the cylinders, or showing low compression?? It was driven hard initially to assure the rings seated, but hey, how can you be sure? Anybody tried the Bon Ami trick to break in cylinders?

 

Thanks Naru for your insight, I am assuming the heads are good as they were rebuilt by a machine shop. And is there any chance of determining ring and cylinder condition without splitting case? The engine didn't use oil before the rebuild and the pistons were cleaned, inspected, and new rings installed in honed cylinders.

[naru]

Since it didn`t use oil before,something altered during rebuilding is to blame.

 

Rings,cyl finish,or valve guide.

 

I wouldn`t assume anything about what the machine shop did.

The same shop installed exhaust guide seals twice.

I would remove those.

 

However,your problem is probably poor ring seating.

I don`t know that you can inspect the cyl. finish visually.

I think you need to deglaze and rering #3 and try again.

 

Here is a good read on break-in:

http://www.ntnoa.org/enginebreakin.htm

 

This is OK too.Nice piston pictures.

http://www.mototuneusa.com/break_in_secrets.htm

Edited January 17, 2010 by naru

[airweld]

Well, we put it all back together without re-ring or hone, as we are in need of the vehicle and it will prove the point if it still uses oil. And if necessary we will rip it apart later when we have more time. No leaks and runs great so far. So, while the engine was out we replaced the front axle due to a torn boot, and the "new" axle is making racket right from the git-go. So much for quality rebuilt axles from O'Reilly's. Lifetime guarantee!