Putting the heads back on today

[liquidlew]

Finally gonna put it back together today, 2 questions: 1/2 turn from zero lash on old lifters (only had the heads done, couple of bent valves) or ? I was told 1/2 or 3/4, so I want to hear what you guys say. And after its adjusted and running, how long should I run it on the muffs? It needs to run for awhile for the head gasket coating to seal? Then let it cool down and retorque or do that when its still warm? Oh, and just how do valves get bent, over tightened? Over rev? The pushrods are all straight. Thanks!

 

[Coors]

Re: Putting the heads back on today

Finally gonna put it back together today, 2 questions: 1/2 turn from zero lash on old lifters (only had the heads done, couple of bent valves) or ? I was told 1/2 or 3/4, so I want to hear what you guys say. And after its adjusted and running, how long should I run it on the muffs? It needs to run for awhile for the head gasket coating to seal? Then let it cool down and retorque or do that when its still warm? Oh, and just how do valves get bent, over tightened? Over rev? The pushrods are all straight. Thanks!

We need more info. It stopped running, or you knew there was a problem-how?
Are there marks on the top of the pistons from valves hitting them?

 

[MikDee]

Re: Putting the heads back on today

I usually adjust the valves 1/2 turn down from zero lash, let it run as long as you want on the muffs, as long as you keep the rpm's down, & the water circulating, so it doesn't overheat. It just needs to run once for a little while at operating temperature, then let it cool down, and retorque the gasket.

Bent valves are caused by pistons, & valves, hitting each other,,, can be caused by a bunch of things: hung up lifters, hung up valves in their guides, bad, or broken valve springs, camshaft, to crankshaft timing being off?

 

[whywhyzed]

Re: Putting the heads back on today

......

 

[liquidlew]

Re: Putting the heads back on today

We need more info. It stopped running, or you knew there was a problem-how?
Are there marks on the top of the pistons from valves hitting them?

1989 Merc 4.3 V6 Alpha one
Wasn't reaching the rpms, should be 4400-4800, and could only get up to 40-4100 trying a few different pitch props so I suspected low compression. Did the comp check and found low comp in #1 cyl so I had the heads done, the rings were ok, cyls and pistons looked good. Got it up and running today on the muffs, runs smooth. Ran out of daylight so I'm gonna recheck the compression tomorrow. Also removed lower unit and am replacing the impeller. Sure glad I got those Merc manuals!

 

[liquidlew]

Re: Putting the heads back on today

We need more info. It stopped running, or you knew there was a problem-how?
Are there marks on the top of the pistons from valves hitting them?

1989 Merc 4.3 V6 Alpha one
Wasn't reaching the rpms, should be 4400-4800, and could only get up to 40-4100 trying a few different pitch props so I suspected low compression. Did the comp check and found low comp in #1 cyl so I had the heads done, the rings were ok, cyls and pistons looked good. Got it up and running today on the muffs, runs smooth. Ran out of daylight so I'm gonna recheck the compression tomorrow. Also removed lower unit and am replacing the impeller. Sure glad I got those Merc manuals!

 

[Don S]

Re: Putting the heads back on today

I look at it this way. The OEM Service Manual (which uses GM information) calls for 1 turn after zero lash. Which basically centers the working parts of the lifter. If that doesn't work, then it means one thing and one thing only. The lifters need replaced or dissassembled, inspected cleaned and reassembled and rechecked. If you have to back off a half turn or more, just to make compression or to get the engine to run right, then the lifters are a problem.

 

[John_S]

Re: Putting the heads back on today

Just follow your Merc Service manual. On latter Merc 4.3L models (SM #18 & #25) it is just a torque setting.

 

[TilliamWe]

Re: Putting the heads back on today

If you ran the engine very long without it being able to reach recommended WOT range, then I'll bet you a nickel that your valves weren't bent, they were tulipped. Does the bottom of your boat get and stay dirty? What props are/were you running?
Anyway, that's how you have low compression but good cylinders, rings, pistons, and straight pushrods.

 

[liquidlew]

Re: Putting the heads back on today

Mine'a a trailer boat so the bottom isn't dirty. The Sea Ray owners info has the stock prop at 21p for my 18'. I tried that, a 19p, a17p ( all 3 blade), and a 4 blade 16. Did tune up and rebuilt carb first year I got the boat because the first time I had it out it was hard to restart after warmed up. See, I did a BIG no-no, I bought the darn boat without checking all the things I should have (and before I discovered this forum) and unfortunately am paying the price. It actually ran great, seemed to have pretty good power and top speed, I just kept noticing the rpms at wot not in the spec range. So I checked the compression and found #1 was way low. The place that did my heads told me I had 2 bent valves, I couldn't tell by looking at them. That shop, plus a couple other marine mechanics I asked all said 1/2 to 3/4 turn on old lifters. We did them all at around 1/2 yesterday and it sounds and runs great now. Bare with me, I'm learning!

 

[JCF350]

Re: Putting the heads back on today

I've started using a compression gauge to set lash on V8 and V6 chevs. For the extra 15 minutes investment, you can see exactly what the valves are doing on the gauge. I hate that 1/2 turn hope for the best crap. I guess from years of working on $50000 diesel engines, I became adverse to guessing at stuff like that.

Like Don says. The amount of turns "properly locates" the center section of the lifter. If it calls for 1 turn then it is centered based on the thread pitch for the correct distance. More or less? and it's wrong.

 

[MikDee]

Re: Putting the heads back on today

I usually adjust the valves 1/2 turn down from zero lash, let it run as long as you want on the muffs, as long as you keep the rpm's down, & the water circulating, so it doesn't overheat. It just needs to run once for a little while at operating temperature, then let it cool down, and retorque the gasket.

Bent valves are caused by pistons, & valves, hitting each other,,, can be caused by a bunch of things: hung up lifters, hung up valves in their guides, bad, or broken valve springs, camshaft, to crankshaft timing being off?

Over the years, I've had friends, & mechanics say, 1/2 turn down lash adjustment works best, and I agree. I found that while adjusting the valves when running, it's a fact that Chevy engines run better, stronger, & more responsive, at 1/2 turn down, then 1 turn down, with no long term ill effects, so it's all good! Regardless of what the GM service manual say's, that setting maybe ok, for a new engine built from the factory, but after an engines been apart, then rebuilt with some wear, & tear on it, I don't think it applies.

 

[JCF350]

Re: Putting the heads back on today

Over the years, I've had friends, & mechanics say, 1/2 turn down lash adjustment works best, and I agree. I found that while adjusting the valves when running, it's a fact that Chevy engines run better, stronger, & more responsive, at 1/2 turn down, then 1 turn down, with no long term ill effects, so it's all good! Regardless of what the GM service manual say's, that setting maybe ok, for a new engine built from the factory, but after an engines been apart, then rebuilt with some wear, & tear on it, I don't think it applies.

Yeah they are funny that way. You would figure it would be the opposite with the way center section moves inside the housing.

 

[John_S]

Re: Putting the heads back on today

The long discussion we had on this in the past: http://forums.iboats.com/showthread.php?t=220365&highlight=valves

 

[liquidlew]

Re: Putting the heads back on today

Thanks all you guys, I didn't mean to cause all this comotion! I read your link John S, thanks, very informative. I got mine all buttoned up and running very smoothly with the 1/2 turn, so I hope I'm good to go. I'll be back soon with more questions as I have my lower unit off and gonna replace the impeller. Thanks!!!