Always had some roughness throughout the RPM range in my 383, so I finally decided to make time to concentrate on finding the problem.
First the engine is a 383 I built from '90 block, Scat rotating assembly, KB-100 .030 flattop pistons, Sealed Power plasma-coated rings, and Brodix IK200 heads. Also running a converted LT1 intake and FAST EZ EFI


I started by running a compression check(cold), all cylinders are coming in @ between 200-210 except for #8, which after doing some further testing, showed a leaking exhaust valve. So I pulled the head, and sure enough, #8 is not seating all the way around the valve seat. Off comes the other head, and off to the shop they are going tomorrow to have the valve seat repair and the rest of the valves checked out.

Here's where things get interesting

#2 and #4 have a couple scratches close to the bottom of their respective bores, not deep, but I can just barely grab with my fingernail.
Also when I did the compression check, I also ran 50psi of air into each cylinder, with each piston at TDC. Found no leaks except through the oil fill on each cylinder. Seeing how this was a cold test, that's probably no cause for alarm. So after doing some searching on the Forum, I found I should have been doing this with the engine at operating temp. So I retest 2 and 4(already knew about #8, #6 is hard to reach at that temp, as are the drivers side bank) and I can still hear air through the oil filler. Not a lot, but it does have me wondering....

Always had a persistent problem with oil in the intake. When I was running the RPM Air-Gap and Holley, I found oil on the bottom of the carb and in the plenum, likely coming in through the PVC. Now its the same with the LT1 intake. I took a close look at the gaskets when I removed the intake the other night, they look uniformly compressed, but the gasket on the bottom of the runners was saturated with oil. This is a Fel-Pro 1206 with the blue seal around each port, plus I put a thin bead of RTV around the back side of the gasket. Don't see how oil could have been getting through, unless it was seeping past the bead. I should also note I am running the stock-type aluminum valve covers and had the PVC valve installed through the cover when running the carb. These covers have the baffles that came with them, could these baffles not be doing thier job?

That's why I'm thinking the rings. This engine can't have more than 5-6K miles on it if that. Running the Sealed Power plasma-coated rings if that makes any difference.

Anyone have any suggestions/advice?

 

For the oil leak I would check the manifold to head gap - gets overlooked quite a bit on rebuilds. Could be the manifold, could be the deck height. RTV can only fill so much gap.

For compression 200-210 is right where I would like to be warm. Cold??? Sounds like you tried a leak-down test the shade-tree way - without a gauged test by audible. Bought my leak-down tester from Summit for < $100. Jegs should have them too. Try a real leak down test once the heads are back on. BTW what was the deck finish for your aluminum heads? Aluminum heads need smooth finish near 25-30 (RHA ?). Iron heads need 50-60 but a lot of stock decks are worse/terrible.

I can't explain the cylinder scratches. Only you and your machine shop can figure that out.

Hope this helps Randy,
cardo0

 

Yep, did it the shade-tree way alright originally I was looking mainly for which cylinder was giving me problems, and I found it

The heads were brand new, so they had a fresh machine finish on them, but it's funny you mention deck height, as this block had been decked before, and I was showing .006 deck height from the top of the piston. However, when I went to fit the LT1 manifold, it seemed to fit fine, and the gaskets showed it had been sealing around the ports, unless as I stated earlier, oil had been weeping past the bead imprinted on the gasket. Mmmm....

 

If the engine was running you could check for blow-by, puffing vapor coming out of oil filler with engine running and the pcv valve out of the valve cover.
You're going to have some air get past the ring gaps, so hearing a little leak isn't a problem.
As far as the roughness, was the engine balanced?

 

Thanks for replying Paul, I see you're local....sort of

I've done the blow-by test you mentioned, no air or vapor coming out
Hearing the air going past the rings was what really got my attention, just a small amount, and you can just barely hear it if you put your ear to the oil filler on the valve cover.

Yes, the engine was balanced by Tom at Balance Technologies in Livermore. I let no one else do my balancing but him, but I haven't used his service since I built the 383 and I hope he hasn't retired!

The roughness issue is caused by a bad valve seat on #8 cylinder. Heads are going in tomorrow for repair/check-out

 

I think I might have met you on the Rainbow Run. Your car looks familiar.

 

You may have. I was one of only three C3's, so my car probably stood out like a sore thumb

 

Took the heads in today and explained the situation to the machinist. He pulled a vacuum on the combustion chambers with a device that looked like a DA sander and found three more valves that weren't sealing, though not as bad as #8. So he'll grind the valves and test the springs $325, guess it could be worse

About the scratches, he said it isn't a big deal long as the compression was good. A long continuous scratch top to bottom would not be good, however he said while I could pull the pistons, hone and re-ring the two cylinders in question, it's not really necessary

 

just started reading the post.... lifters out of adjustment will cause a lot of the blow by systems, and also if not adjusted properly could keep your valves slightly open.... i would definitely examine the valve train..

 

Sounds like you are doing the correct tests at this point. I'm not sure if the heads were bad enough to cause the rough running. Did you try checking the cam lobe lift for consistancy?
I wouldn't rehone the two cylinders to clean up any mark. That would change your piston clearance on those cylinders. A mark that direction almost would have to be something the cylinder hone made, It looks like they haven't had an effect on your compression.

 

Lifters were adjusted at TDC, turning the pushrod till I feel slight resistance, then tightening 1/2 turn. I hope I don't stir up a hornets nest here, I know there's been some heated debates about the "correct" procedure, but this has always worked for me


Never thought to check the cam as you described, though I have mics and it would have only taken a few minutes

Here's the valve seat causing the problem. I can be fairly certain this is what was causing the low compression in #8, and the roughness throughout the RPM range. I should have stated in my original post it's a "slight" roughness, not causing a bad idle or excessive shaking, but enough to know "somethin' ain't right"
BTW the valve is not bent, I chucked it up in the lathe with a collet and ran a dial around it, it's perfectly straight

[IMG][/IMG]

 

How does the guide look? Valves were adjusted just as I do them. But I know what you mean about debate. I've heard 1/4 to 3/4 turn, but half has always worked for me.
I have an old valve cover cut up and welded as a shield to permit me to adjust without a mess of a great degree. I have the oil blockers that helps some but the old valve cover works like the shield on my rod reconditioner does.
When your machine guy does the head he'll find any bad guides.
A few years ago, there was a guy selling seconds heads that had all sorts of small issues and some large issues, that if weren't checked very closely could be over looked.
Not that yours were, but it was funny, he had a truck full and sold them at a swap meet one year. If he had come the next spring to the same swap meet, there would have been a Tar and Feathering as it seemed like everybody was after him. Some of the issues were guide related.

 

As far as blow-by goes, i had 3 roller H-lifters go bad, the would not hold a pump (in various amounts) and thus not working properly... car ran a little rough but still ran, in fact, it pulled at that time with 3 bad lifters on the chassis dyno 380hp anf 436tq.... so she pulled good, just not GREAT... replaced the bad lifters... and 440-460hp appeared...... AND I always had a lot of blow-by..., but again, after replacing the 3 bad lifters my blow-by went down 98% ...... this is the reason i said to check the valve train... when i first adjusted them i did as you. but with a feeler gauge.... and I would have never noticed the problem if i had not upgraded the RR's and in the readjust it came to light.... just a thought

 

Sounds like someone may have got to him first before he had a chance to return. Things like that have a way of coming back
The guide looked fine, no excessive play. I think .001-.002 is right IIRC


What's the proper way to check a lifter to see if it's holding pressure? If they need to be removed to check, now would be a good time

 

The reason i did not find out the first time is that i adjusted the lifters without any pump... went to 0 lash and +3/4, in my case ( but was using the feeler gauge to get the exact lash needed).... so all felt the same...but i goofed, i left all the locknuts loose and they all went out of adjustment in about 60 seconds!!! AAAGGHH!!! i was so sad... all that time and working to get a perfect backlash with the feeler gauge for nada!!! so, now all my lifters had a good pump to them and so i just went back to 0 lash and +3/4 as I previously learned that was the right amount for me via feeler gauge. but now that the lifters had pump it became obvious that 3 were not anywhere as hard as the other 13, which were holding there pump and rock hard. Called CompCams, and yup... they said they were bad, and replaced them all...

 

Addressing the oil problem, the lower part of the intake manifold gasket may not be sealing properly with the runners of the heads. The Fel-Pro 1206 has large openings, perhaps quite a bit larger than the runners in your manifold. You could try the 1204 or 1205 which have smaller openings and may be a better match.

Further, if your heads have a larger combustion chamber than 64 cc, they may have a higher intake manifold bolt height above the deck which can hurt alignment. In that case, you'd want to use a thicker intake manifold gasket to get best bolt hole, port & runner alignment.

 

Another thing to add to the checklist

 

1205's are too small.Tried them already, but I may look into the thicker gaskets and see what's available

 

I took your advice
I chucked a pushrod in the drill press and set each lifter in a wood block fixture I had made. #1E and #2I sink about halfway, and #2E sinks right to the bottom. The rest are holding fine. Looks like I'll be adding three more roller lifters to my shopping list
Thanks for the tip Paul

 

See you on the PCH cruse!!!