Leaky exhaust valve

[larrym]

So I was struggling with what I thought was a severe vacuum leak low 02 and bad idle vacuum gauge was at 12. Pulled the motor and put it on a stand to get to the bottom of it. I had done a compression test and all were at 150 except #5 it was 135.
I pulled the rockers and pressure tested the intake looking for my vacuum leak it was fine. Pressurize #5 air was spewing out the exhaust port that explains the lower compression whacked it a couple times with a hammer no change. Checked all the others they seemed fine. Off comes the intake so I can pull my head found #4 gasket pushing into the valley next time I hit it it was done.

 

[TURBOELKY]

Damn good catch right there my friend.

 

[larrym]

So do you think I can seal it up with lapping compound?

 

[fastblackracing]

Those pits look fairly deep, I would put the valve in the head and put the cordless drill
on the stem and let it have it with a bunch of applications of lapping compound or better yet if you can
find it some coarse 80 grit grinding compound. Work it for a bit both directions and clean it up and have a look at it.

I have brought some daily driver stuff but to life doing it this way with good results.
Mcmaster Carr....very easy place to deal with. see if you can find a branch near you.

For fast lapping on most metals, these pastes contain silicon carbide, which is very sharp and abrades quickly.Apply them to your workpiece with cylinder laps, buffing wheels and bobs, and lapping and polishing sticks.The microns and grits listed are approximate. Size is 16 oz.

Oil-soluble pastes won't cause corrosion. Use water-soluble pastes where oil could contaminate your worksurface.

Oil Soluble
Water Soluble
Microns Grit Each Each
Smooth Finish
267 80 4779A86 $33.98 4908A56 $33.77
173 100 4779A52 33.98 4908A55 33.77
142 120 4779A46 33.98 ______ __
86 180 4779A41 33.98 4908A52 33.77
Extra-Smooth Finish
66 220 4779A35 33.98 4908A51 33.77
63 240 4779A29 33.98 ______ __
44 280 4779A24 33.98 4908A48 35.40
33 320 4779A18 35.68 4908A47 41.69
Polished Finish
23 400 4779A13 35.68 4908A46 42.92
14 600 4779A76 56.46 4908A44 67.09
9 800 4779A96 75.62 4908A43 68.47
5 1000 ______ __ 4908A42 67.09
3 1200 4779A98 78.28 4908A41 81.89
Each
Oil-Soluble Assortment–Includes 2 oz. each of the following microns: 142 (smooth) and 44 (extra smooth). 4779A42 $15.05

 

[TURBOELKY]

Are you referring to the oil around the guide area or are you sure it leaked around the seat?

And lapping the valve in really is not idea. That head and valve both lack a performance valve job. I would just spend a couple bux while the heads are off and get a performance valve job done. Should run $250-300 for both heads

 

[larrym]

I spent 800 dollars on these heads having them decked new guides put in new springs and I insisted the tips were all set at the same height.
That's after I spent a week porting them.
Pretty disappointing to see this and hear it's not a "performance grind"
These were done last spring and I bet it leaked from day 1.

 

[TURBOELKY]

All I see is the valve has its 45* as it probably came from wherever you bought them, that way. Your head has a 45* seat and maybe a 30* above that. Usually want a 60* below the 45* and if the machinist is bad ass, he will pull out a serdi cutter and put a couple more angles in there. I usually put a 30* back cut on the valve above the 45*. Low lift gains improve significantly, all these small improvements make that port function as soon as that valve cracks open.

 

[larrym]

Hmm I thought that's what I paid for I gotta find my receipt. I'm not sure that I'll go back to this shop even if I did....

 

[TURBOELKY]

Maybe its there and I just can't see it in the pic? the seat its hard to tell, I'm pretty confident the valve is just a 45. I've been wrong in the past...

 

[larrym]

No you are correct found my receipt no mention of a performance grind.

 

[ek02]

Looks like 3 angles, but with the bowls ported to the 60 degree bottom cut, and the 45 degree seat already at the outer edge of the valve margin, it's as good as it can be. I would try the course, then fine, valve grinding compound. If that does not work, it would just need a touch up with a 45 degree stone. Looking at the exhaust valve stem, it looks like a stock valve. I would guess that the exhaust guides were not cut for seals?

 

[TURBOELKY]

Maybe there is 3 angles in there, hard to tell. That valve may be stock, I thought I remember mine having GM in the casting. Either way, I've got the stock exhaust to flow great with a proper valve and seat grind. If I tried to do any valve work with lapping compound I would get thrown out of the shop. This is a performance engine, not a model A... Take the heads back and have them touched up with a stone. Have the rest checked while they are off the car.

 

[larrym]

They are oversized stainless valves and its single angle from what I can see.

 

[earlbrown]

O/S exhaust valves won't have the 'ski jump' the stock units do. There is a BUTTLOAD of flow just doing a back cut on those.

...that being said, 'oversized valves' are the same size on exhaust. 1.500". Intakes go from 1.700" to 1.770", and that extra .035" of radius damn near makes them touch.

I did notice on your receipt, it shows 'valve guides' but your pics look like those brass liners, not guides.


Here's the 'problem' with lapping valves... Lapping, by nature, is a way to hand machine two parts to marry them 'perfectly'... When it comes to valves and seats that goes right out the window when the engine gets hot. The seat is cooled by water and will expand just a little.. The valve runs MUCH hotter and will expand more. Just from thermal expatiation alone, it will swell and move upwards on the seat towards the combustion chamber. When that happens, you're 'perfectly married' lap lines are no longer touching.

 

[larrym]

So the heads are back on he charged me $90 to repair the 1 seat and clean the head installed 3 new positive seals and gave me 3 for the exhaust guides on the other head 4 were off the guides and floating old ones were the stock felpro new ones were a solid steel cap. He said my back pressure was pushing it off I'm sceptical. Pressurized it its sealed so I'm happy. Degreed the new chain it's 1 degree retarded so I installed it 4 degrees advanced figure by the time it stretches I will be 2 degrees advanced.

 

[TURBOELKY]

Good news man. Glad you had them checked and repaired.

 

[earlbrown]

If ''backpressure'' pushed your seals off that means they left the stem to guide clearance too loose.

It would also displace the oil needed to avoid smoking the valve....

I'm not buying it.

 

[larrym]

And they were tight his exact words were I have seen this before on high boost diesels.

 

[larrym]

so if it was yours car and you had a choice on cam timing would you run it 2 degrees advanced, 2 degrees retarded or 6 degrees retarded. My turbo spools pretty quick and lag is not really an issue.

 

[earlbrown]

And they were tight his exact words were I have seen this before on high boost diesels.

You need a new head guy.