Light white smoke and backfire at high RPM or under load

[iflyfisher]

I am losing my head(s)!!

I finally got to checking the compression this morning. I took the truck out for a short run to warm it up then pulled the plugs. This is the first time I had pulled the plugs since putting a bit of time on the engine. I pulled 1, 3, and 5 and each of the plugs had a nice light tan color. I pulled 7, and it was black and sooty. I thought, "ah...ohh." I switched over to the other side. Plugs for 2, 4, and 8 again looked great. But 6 was black. I checked the compression and all the cylinders where the plugs looked good had compression between 148 and 150. Numbers 6 and 7 were 85 and 45, respectively. I have my Dad's old logs, which has an entry for 1975 at 20,390 miles, and the compression figures for all cylinders were between 140 and 148. So 48 years and 80000 miles, and the compression is relatively unchanged for 6 of the 8 cylinders. Given most of the cylinders show no decline in compression, I suspect valves rather than rings. Guess this answers the question of my original post. I probably should have checked compression first thing. But the other things I did were likely needed anyway, plus I learned a few new things.

Time to spray some penetrating oil on the exhaust manifold and head bolts then read up on how to pull the heads. It doesn't seem complicated as long as the bolts cooperate. Also, I will need to find a shop to seat the valves for me. One question I do have is do I replace all the valves while the heads are off? Maybe the answer is to wait and see what the others look like.

One more thing I haven't done before!

Ken

 

[WFO]

I am losing my head(s)!!

I finally got to checking the compression this morning. I took the truck out for a short run to warm it up then pulled the plugs. This is the first time I had pulled the plugs since putting a bit of time on the engine. I pulled 1, 3, and 5 and each of the plugs had a nice light tan color. I pulled 7, and it was black and sooty. I thought, "ah...ohh." I switched over to the other side. Plugs for 2, 4, and 8 again looked great. But 6 was black. I checked the compression and all the cylinders where the plugs looked good had compression between 148 and 150. Numbers 6 and 7 were 85 and 45, respectively. I have my Dad's old logs, which has an entry for 1975 at 20,390 miles, and the compression figures for all cylinders were between 140 and 148. So 48 years and 80000 miles, and the compression is relatively unchanged for 6 of the 8 cylinders. Given most of the cylinders show no decline in compression, I suspect valves rather than rings. Guess this answers the question of my original post. I probably should have checked compression first thing. But the other things I did were likely needed anyway, plus I learned a few new things.

Time to spray some penetrating oil on the exhaust manifold and head bolts then read up on how to pull the heads. It doesn't seem complicated as long as the bolts cooperate. Also, I will need to find a shop to seat the valves for me. One question I do have is do I replace all the valves while the heads are off? Maybe the answer is to wait and see what the others look like.

One more thing I haven't done before!

Ken

Before tearing it down, I'd squirt some oil into the bad cylinders. If the compression comes up it's rings.
Just to make sure it's loosing the compression from the head gaskets up.

 

[iflyfisher]

Thanks @WFO, I’ll do that. I had just assumed as the other cylinders were good, it was valves. Another reminder of how little I know.

Your comment does have me wondering though if the compression loss is due to rings, could the rings in those two cylinders be stuck? I would have thought that with a half tank of fuel through the engine that any stuck ring would have been loosened up by now. I’ll squirt in some oil as you suggested and go from there. Thanks again.

 

[iflyfisher]

Providing an update as a couple of weeks have passed since my last post. I put some oil in the cylinders to check whether the leak was rings or valves. The compression numbers did not change. I ran a can of CRC valve cleaner through the intake. No change. I pulled the valve covers and removed the rocker on the suspect cylinders and rapped on the valve with wooden block and hammer. No change. I had been running some cleaner through the system with my fuel and using the truck to run errands. Still no change. I wasn't sure what else I could do, so yesterday, I pulled the heads. I found a local machine shop that will rebuild the heads for me and dropped them off this morning. Prior to taking in the heads, I put the spark plugs back in the bum cylinders along with an adjacent cylinder and flipped over the heads. I filled the valve cavity with denatured alcohol to see if the valves were indeed leaking. Yep. They leak.

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Shop said the heads should be done next week. I won't be able to get the engine back together until after the new year. I talked to the machinist, and he said pull the lifters individually and make sure the bottoms are still flat then drop them back in the same slot. Need to get some gaskets ordered. Do I replace any of the head bolts? They seem fine, but I don't know if one is supposed to replace them. Going to do some cleaning on the rest of the block and engine bay while the top end is out.

I had thought about putting some headers on the truck and converting to dual exhausts while I have the exhaust manifolds off. However, after reading through many of the header related posts on the Forum, I think I am going to stay with the stock exhaust manifolds and convert to a dual exhaust some point later. This truck isn't going to be my daily driver, so I'm liking the idea of staying with the current performance and keep the truck closer to original.

 

[Snoots]

I've always been told to NOT re-use head bolts. I didn't on my 2 rebuilds so I don't know what to tell you other than new bolts are cheeper than a broken one.

 

[PrairieDrifter]

We almost always ran the used head bolts on our rebuilds at the shop. Just clean them up really good and give em a look over.

 

[iflyfisher]

Thanks @Snoots and @PrairieDrifter. Set of new bolts for the heads is $28 and on sale at 20% off, so may just replace those given the nominal cost. I felt lucky to remove the exhaust manifold bolts without snapping one. I definitely want to replace those, but I can't find any online at Napa. Are the exhaust manifold bolts the same as used in the Chevy LS?

 

[PrairieDrifter]

Thanks @Snoots and @PrairieDrifter. Set of new bolts for the heads is $28 and on sale at 20% off, so may just replace those given the nominal cost. I felt lucky to remove the exhaust manifold bolts without snapping one. I definitely want to replace those, but I can't find any online at Napa. Are the exhaust manifold bolts the same as used in the Chevy LS?

Definitely count your lucky stars you didn't break any manifold bolts.

Regular 3/8 bolts. Depends on your manifolds for the length. Just measure a hole depth to the mounting surface and the manifold thickness.

 

[iflyfisher]

Thanks @PrairieDrifter

 

[squaredeal91]

I've never even thought about replacing head bolts on a small block before. Clean em and inspect like @PrairieDrifter said.

 

[RanchWelder]

You will do well to ask your machinist to verify your intake manifold is not warped before you just bolt everything back together.

 

[iflyfisher]

@RanchWelder, thanks for the tips. I'll take in the manifolds when I pick up the heads and have the machinist check them for flatness. The engine hasn't overheated since I got the truck a couple of months ago, but I don't know prior to that. My Dad generally kept the truck well maintained and never pushed it hard. It probably only averaged a couple thousand miles a year over the past 40 years. I suspect the valve issue is more with age than abuse. I hadn't planned on replacing the timing chain/gear yet. I didn't pull the engine, so that may wait until I remove the front body components as part of the resto. Unless of course, the engine still isn't running right after installing the new heads. Then I'll do the timing chain next. I rebuilt the carb shortly after getting the truck but curious as to who are the 'Good Guys'?

 

[iflyfisher]

Well...I feel a bit like I'm playing Whack-a-Mole. I pulled the lifters individually to inspect them. All looked good with the exception of the No 3 exhaust. Looks like this lifter has not been rotating for some time. Arghh! I'm guessing this means a new cam. I can't seem to get ahead in this 'get the ol engine running' game.

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[squaredeal91]

Luckily at this stage A cam is easy to replace. And we'll worth it.

 

[PrairieDrifter]

It's a small block Chevy... just did my head gaskets with the old bolts. got 5,000 on it no problems.

Not much more to say than it's an old chevy. Maybe a ford would care about that crap...

That lifter is junk though.