SBC engine trouble

enkeivette

enkeivette

Well-known member
Joined
Mar 30, 2008
Messages
990
Round two.

Replaced my blown up piston and all 8 ring sets. Fired the motor up, straight headers, let it get hot, retorqued the heads.

The next day I bolted up the exhuast, let it get up to operating temp and set the timing. It was running fine, sounded normal. Turned it off to inspect for oil leaks, fired it back up and the exhaust sounds really loud and poppy on the drivers side. The exhaust is connected by an H pipe, but other than that it is pretty much straight through. I would think this would be an indication of something wrong on the drivers side.

Did a compression test, 130-135 in all cylinders except the one that I replaced. That cylinder is at 115 psi. But that cylinder is on the passenger side?! The low psi could be a result of the scored cylinder wall, a crack in the head, a f'd valve seat or some melted aluminum on the valve. But, all of these things would have existed during the initial and 2nd start up. The loud poppy exhaust note (exclusively on the drivers side) started later. So what the hell could it be? What does that sound indicate? Tomorrow I'm going to pull the blower off so I can pull the valve cover off and watch the rockers moving. I'm thinking it might be a stuck lifter...???
 
It could be a lean misfire on one cylinder or a rich condition burning in the exhaust, a mis adjusted valve (not closing)....and so on. What worries me are those seriously low cranking pressures. Even with a low CR (do you have a low CR?) it should have been a lot higher, easily over 160. Did you test it with the throttle fully open? How many cycles?
 
Twin_Turbo said:
It could be a lean misfire on one cylinder or a rich condition burning in the exhaust, a mis adjusted valve (not closing)....and so on. What worries me are those seriously low cranking pressures. Even with a low CR (do you have a low CR?) it should have been a lot higher, easily over 160. Did you test it with the throttle fully open? How many cycles?
Click to expand...

They bother me too. I think the cause is a 110LSA, 6" rods and only 9:1 static. It bothered me so much that when I replaced the piston, I decided to replace the rings on all 8. Always thought something was wrong with them. But I get the same number now as I did before.
 
Did you at least hone the block w/ a bubble hone? The rings not having seated somewhat explains the low values if not honed they will never seat however and you'll bake all the rings full of oil. Scratches explain the even lower value for the damaged bore. I sure hope you at least removed the glaze (but I feel glaze breaker hones suck)
 
Motor only had 8K miles since bore, don't think it needed it. I removed the melted aluminum with hydrochloric acid and a bronze brush. But this isn't the issue.

Pulled the plug wire off #3 and the funny exhaust noise stopped. Number 3 is the piston that was damaged slightly when the other piston exploded, but it cranks out psi like all the others, so I doubt it's broken.

And like I said, noise was not present during initial 20mins of run time... :confused:
 
Loose exhaust rocker. Would have found it two days ago if I didn't have to pull the blower off to get to the rockers.
 
I kind of hate to say this, but it makes a very good case for adjusting hydraulic lifters with the engine running. Even if it is messy.
 
Why was it loose ? Did you re-use the rocker nuts ?? Hope you've got the locking style rocker nuts.

I had trouble with used rocker nuts and bought new ones at the Zone, at the time I did not want to order online and having to wait two days....
 
Okay, so the weird sound culprit is found still leaves the low cranking pressures. Hate to say if but if you have moly faced rings they will never seal, a soft cast iron ring may give a somewhat acceptable seal but w/ 6K on the bore faced rings will never fully seat. Time to throw some VIM down the intake ;)
 
mrvette said:
TimAT said:
I've never seen VIM here TT. We use Bon-Ami and Coca-Cola. :D
Click to expand...

:stirpot:WTF you guys talking about????

:noworry:
Click to expand...

VIM is magic cleaner, much like Bon Ami, only better. I think that the grit is finer and cleans better.

I still buy it by the case when I'm back in the homeland for visits.

Glad you solved the original problem at least.
 
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