Help my 350 now sounds like a diesel here is what has been done I pulled the engine to replace the pistons the engine was rebuilt with 24cc pistons I had the engine honed replaced the pistons with 6cc pistons and new rings reused the old cam and lifters make sure to put each lifter back in the same location it came from. I also changed over to comp cams roller tip rockers and new push rods and a new Cloyes timing set.


I checked the rockers are not hitting the valve covers and I even put the old non adj rockers and push rods back on and it still sounds the same. Also checked the fly wheel, torque converted, fuel pump, and ran the engine with all the belts off.


Could I not have the valves adjusted correctly.


Thanks for the help.






[URL=http://s20.photobucket.com/albums/b229/70cutlass/?action=view&current=cutlass008.mp4]

 

Where is the noise coming from?
Timing set correctly?
How's the oil pressure?
How much piston to wall clearance?
If you used a thick head gasket, you could've decreased the lifter pre-load!

Just a few things to look at and consider.

 

When you say it sounds like a diesel, do you mean this is a detonation sound, or a mechanical sound? What heads are you running? If you went from 24cc pistons to 6cc pistons, you increased your CR, did you CC the heads and calculate your CR? According to my very vague calculations, if you've got 1970 64cc heads and your initial CR was around 10:1 with 24cc pistons, then it's up somewhere around 12:1 with 6cc pistons, which could have a lot to do with your problem. I may be completely off base here. Hopefully someone with more engine building experience will chime in.

 

Thx for the reply’s
I have the timing set @ 20® BTDC 35 total @about 3200 oil pressure is @ 50 psi on startup and drops down to 20 at idle 900 RPM and goes up at the RPMS go. I used the same kind of head gasket a new felpro .045. I need to check on the piston wall clearance I don’t have that info with me they are 6cc diamond pistons.

With the old heads I had about 7.82 compression 64cc heads I cc’ed them pistons were 23cc (went back and checked pistons were 23cc) and were .40 from the deck and head gasket was .045. With the new pistons I should be at 9.8
Not sure where the sound is coming from it seem to go away at the RPMS increase sounds like the valve train but I am not sure my fear it piston slap.

 

My initial impression was a rod bearing but you say the sound goes away with RPM?

Piston slap would also be aggravated by RPM so I wouldn't think it is that.

 

Rods knock loudest on the rev, pistons on the decel of rpm. Main knock loudest at idle. Valve train, it usually doesn't matter. That's my experience. After seeing this written down, it could be the reverse. Don't ever get old. It is backwards: pistons on the rev, rods on the slack.

 

Link to video added. open to any suggestion.


http://s20.photobucket.com/albums/b2...tlassagain.mp4

 

I don’t have speakers or I’d listen to your video.

Does the sound get quieter as the engine warms up? How many miles are on the engine since you changed the pistons?

Take a long screw driver or stethoscope if you have one and try to narrow down where the sound is the loudest. It sure sounds like a wall clearance problem, or even a pin issue, since you just had the pistons changed and the walls honed. See if the shop that did it can give you the specs.

I gotta get some speakers on my pc!

 

I hear a lot of wind noise in the video. It'd help a lot if you took the belts off and just ran the motor, not the fan, for a minute. Bring a light to the gages area too.

I am going to say.... probably.... if you changed pushrods, added thicker head gasket [raising the rockers a few thou].... what you hear is valvetrain clatter. I experienced that on a 403 I bought- PO had put a wild cam in, but never set lifter preload correctly. It was 0 or less- clattery lifters.

Do you know how to set lifter preload? Last time I dared to suggest that to helpee I got my head chewed off.

unless of course your 350 -IS- a Diesel!
:-)

Then, it sounds perfect!

 

I am not trying to second guess your work; everything that has been done sounds reasonable and you may have checked something but not mentioned it. New parts mixed with old often show up the weakness and wear on the old parts.

Olds engine lubrication can be tricky. Gauge pressure is only reliable at the gauge port and doesn't mean pressure is good everywhere. Is everything getting lubed? Are high zinc break-in lubricants being used? Are all internal plugs in place? Are all oil passages open and lined up and not obstructed?

What happens when the ignition timing is backed off a few degrees? Is everything tight and settings are not erratic when the engine is rev'd?

It's important to eliminate possible problems or weaknesses. Consider the crankshaft and eveyhting it touches and everything those parts touch all the way through to the valves and sparkplugs.

This may be a lot of work but remember GM 350 based diesels didn't last long.

Thanks. Dick

 

Olds hei if that's what you have. Come with 20 degrees of advance 20 initial will be ticking through the entire rpm range Up to 40 degrees. I bet it would sound like a diesel. Back the timing off to about 14 to start and listen from there.

 

I think that's maybe too much initial also, but I don't think it would make it sound like that at idle. It sounds mechanical to me. You need to change the breakin oil anyway, so check for metal filings. You will always have some on a new engine, but if it looks like etch a sketch, you may have a bigger problem.

 

I know I dont have much motor replacing experience but actually my cutlass v6 had this exact same sound for a month out of no where and ending up it being the crank or crank bearings. Just my imput

 

I'll just shoot for the easy ones - exhaust leaks? Looks like you have a set of headers. With the engine really cold, start it up then feel around the header flange for leaks. Can make funny sounds.

 

This should be a good one. I once pulled a motor because of I thought a rod starting to go. Only to find out it was crank bumping the end of the dipstick on the way by.