Thread: my 355 sounds like a diesel

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Please help I have a 350 small block, with angle plug dart heads,flat top forged pistons, steel crank, floating rods and crane energerizer cam and lifters block is 30 over crank is turned 10/10. Motor has 35 psi oil pressure at idle, motor has 1 hr. on it cam was broke in proper, my problem is motor sounds like it's dieseling sound seems like it's coming from under intake really bad when engine is cold but still there when engine is warm. Has anyone else had a problem like this? P.S ready to tear motor back down.

What is your ignition advance? What is your compression ratio? Are the pistons loose in the bore? The oil pressure is good which leads me away from excessive bearing clearance. The fact that it gets better as the engine warms up makes me think it's piston related. Are you using forged pistons? Forged pistons expand more and must be fit loose in the bore so they have room to expand as they warm up. When the engine is cold, the skirt will slap the cylinder wall making a diesel noise. Did you use hypereutectic pistons? I have heard stories that some brands of pistons run tighter clearances than standard pistons, but some shops forget to take this into account and machine the bore for standard pistons. This results in piston slap/diesel sound.

Thanks for the input 76GMC1500 my ignition advance is 10 degrees advanced compression ratio is 10/1 cranking compression is 185 and i am using trw Forged pistons wall to piston clearance is 5 thousand noise is still there when engine is warm but not as bad

Originally posted by 4onthefloor
my problem is motor sounds like it's dieseling

What is your cranking compression PSI?

Sounds like you may have a mismatch between your static compression ratio and your valve timing.

cranking compression PSI is 185

Originally posted by 4onthefloor
cranking compression PSI is 185

I'm not familiar with the Crane cam you're using but if it is designed for low RPM torque and your static compression ratio is around 10 or 11-1 that could possibly be your problem. The "torque" cams are designed to be more volumetric efficient in the lower RPM ranges and generally work best with static compression ratios ranging from 8.5 to 9.2-1.

You might try dumping some racing gas in it and see if it quiets down. If it doesn't you should probably look for a mechanical cause.

I had the same problem with my 350 rocket in my truck. This is gonna sound stupid but check your vacuum that's what mine was. If that ain't it check your timing and compression ratio thats all I got to say on the subject

Did you lube the cam or lifters when the engine was assembled?Lifter noise can cause a lot of noise. Also check the fuel pump rod ive seen it cause a lot of noise also. Just some simple thing to check before you tear it down. Sometimes its the simple things that cause a lot of problems.

larry tell me what think

Originally posted by j*b
I'm not familiar with the Crane cam you're using but if it is designed for low RPM torque and your static compression ratio is around 10 or 11-1 that could possibly be your problem. The "torque" cams are designed to be more volumetric efficient in the lower RPM ranges and generally work best with static compression ratios ranging from 8.5 to 9.2-1.

You might try dumping some racing gas in it and see if it quiets down. If it doesn't you should probably look for a mechanical cause.

I'm not a first time engine builder and this won't be the last, my engine is a fresh 355 with moley rings TRW forged pistons,floating rods, steel crank, cast Dart 2 heads,with 205 intake and 160 exhaust stainless valves crane energizer cam, , with 1.5 roller rockers, Elderbrock torker2 intake, MSD ignition 6A , with a 750 holley carb compression ratio is 10.14 cranking compression is 185 psi per cylinder the motor is in a 1968 Chevelle 2 door sports coupe with a 4 speed saginaw rear end gears are 411 in a 12 bolt posi with ladder bar suspension motor sounded like it was dieseling while running sound came from below intake I ripped the motor down all I found was cranes lifters had 8 parts to them never seen that before but I totally tore motor down to nothing after 1 and a half hours of running time oil pressure was between forty and up I'm not sure whether it's piston slap or cranes lifters all bottom end specs are perfect PS I'm Canadian my brothers crossing the border at Christmas says he can get me a gear drive for my sbc what do you think of noisy gear drives Thanks to all you guys for your input