forged piston slap sound with a twist ?

[magnus4g63]

Hi Guys

Im kinda new to forged pistons so I hope someone can answer.

After doing some reading in here I can understand that a diesel like sound is normal when the pistons are cold.

I just did a rebuild of my 1g with wiseco / eagle and had the best (i think) guy i could find in my country to do bore / hone / rings so that this would fit perfect.

Thing is that I have this wierd diesel sound in idle when the engine is warm ... not when it is cold .... thats the twist

Ofcause in a panick i replaced EVERYTHING to do with cams and lifters as i thought that the problem was related to that ... no change.

Everything in the engine is new

Could this diesel like sound be my pistons? what could be going on? am i looking at engine failure soon ?

Engine runs great no smoke no oil consumption ... making 340 whp

Please answer

Best Magnus

 

[xx1gdsm]

are you running just open down pipe or do you have a full exhaust?

 

[magnus4g63]

Hi

Im running full exhaust 2.5" all the way with 2 simon and an Apexii WS2 at the back (sounds great)


I should ad that the diesel like sound is there when cold but very very low and quickly increase to real diesel engine like volume as it heats up

Engine oil is castrol 10w60

 

[BogusSVO]

did you check your piston to wall clearance when the engine was built??

 

[magnus4g63]

well no .. i didnt

I had bottom end done by a pro. he asked for the pistons before doing bore and hone so that he could match them perfectly ... if he f´d up im going to complain.

I just dont know if he did, i guess i have to open her up and check ?

... But is it possible that the problem is pistons, when the engine is cold there is no noticable noise and when its hot there is ?

If it is piston slap, will this damage the engine ?

thanks for your interest

 

[tenn-gsx]

Had this issue 6.0 VOTREC when they first came out. We (Me and the other GM techs at the dealer I worked at) tore that engine apart 3 times before we found the problem. We had to replace the headgasket due to a bad HG leak under warranty. This was 2000. First year of the new vortec engine. Went to the parts dept and picked up all the parts. Put it together and it rattles like a diesel. Tore it back apart and tried again. Same thing. One more time and I noticed this little tiny clean spot on the edges of the pistons. Laid the used Hg back on and realized that we had a 5.3 gasket. Went back to the parts dept and asked for the correct gasket. Laid it on and the same issue. So we decided to pull a 5.3 gasket off the shelf and it fit. Turned out that GM mixed the 2 part #s up. Good for me it was a parts supply issue otherwise I would have been out a day and a half of pay. So basically im askin are you sure you have the correct headgasket bore for your engine bore?

 

[magnus4g63]

U R THA MAN

this could be a real cause ... im using a cometic HG and that could be standard bore size ... im not really sure, cant remember

Pistons are oversize for sure ... ive done like 4000 miles with my diesel idle, are my pistons damaged given the HG is wrong bore ?

Thanks

 

[tenn-gsx]

Most likely not but possibly damaged. If this is your situation.

 

[magnus4g63]

this is great

dont realy care if stuff is broken, just like to know why. Been spending more money on tuning stuff than i ever would just buying a fast car anyway.

Been planing on bigger turbo and using the engine in another car so when i do i will update this thread so that others that might have the same problem can find out why

Back to the 2jz ... love that thing ... 610hp on stock internals .. nooooo problems

Thanks again

If somebody have another explantion please do share

 

[HIGHPSI4]

Really sounds like the piston to wall gap is too small. Head gaskets can cause hot spots sometimes and you may hear this as spark knock, but should not affect the piston due to the fact the piston should not touch the HG.

 

[redline2]

Agreed, check the piston to wall clearance and your stroke.

 

[jay4725]

I would like to see what the problem is, so when you do find out please share.