Built engine. less slap and less smoke now..

[azoil]

4cyl built engine. Forged pistons on the loose side. Slaps at idle. Worse when cold. Broke in on 10/30 dino oil for 3k miles. Smoked the entire time. then 15/50 Mobil 1. Same smoke, same slap. Ran for 4k more. Then changed oil and parts store was out of 15 so I got 10/30 mobil 1. Half the slap... and no smoke. The slap is there still.. but its not nearly as bad as it was. Drove 1000 miles. Does not need a top off.

I am stumped as to why a lighter oil makes less noise and does not smoke. Can someone school me?

 

[Ray H]

Lets play, "Guessing Game": Two syns. from the same refiner. One has a 20 pt. viscosity spread. One has a 35 pt. viscosity spread. Guess which one has more added VIIs. Guess which one may not even have any added VIIs because the base oil content may handle the listed spread without additional help. Guess which one probably shears back more after a couple thousand miles.

Was there a reason you went with looser pistons?

 

[forcedtalon]

High boost most likely. I have my ross'es set at .0045-.0047 and doesnt slap at all mine never smoked at all with 10/30 M1 EP. Could it be the hydrolic lifters making the noise?? I dont like the heavy oil. It slows down the turbo spooltime and just harder on the oil system. I am going down to the amsoil 5/30 s3000 or the 0/30 2000 to get bettter gas milage and faster spool. The only time I would use a heavy oil is on an road race motor that sees 1/2 hour abuse. The 15/50 does more harm than good on a street motor even if it gets driven hard sometimes.
If you know its piston slap maybe try some 5W40 M1 truck and suv if a hvy oil is need.

 

[JohnBrowning]

It is normal to get more slap with forged pistons until up to operateing temp. A lot though has to do with how well your machinest did his job? I have had plenty of engines with forged pistons that had no slap at all unless it was winter time and even then it was minor. If you have slapp issues you need to talk to your machineist!!

 

[427Z06]

quote:

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Originally posted by azoil:
I am stumped as to why a lighter oil makes less noise and does not smoke. Can someone school me?

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I did read study where thinner oil resulted in a thicker oil film somehere on the piston, IIRC. Can't find it to save my life now. Not sure if that's what you're seeing in your case.

 

[JohnBrowning]

427Z06, I think it was a Shell paper and I think it was mostly talking about the piston rings. Hope that helps jog your memory!

 

[XS650]

quote:

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Originally posted by JohnBrowning:
427Z06, I think it was a Shell paper and I think it was mostly talking about the piston rings. Hope that helps jog your memory!

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Was that the one written by a Brit academic?

 

[forcedtalon]

Also I forgot to add that forged forged pistons need to be machined AND honed with a torque plate so when you bolt the head on it doesnt distort the cylinders .

 

[theguru]

Mobil1 10w-30 became the recommended oil for the piston slapping V8's here in Oz.

 

[azoil]

Hi guys. Yes.. This motor slaps. It is 100% piston slap... Valve train is silent. It was built by a well known import engine builder and The pistons used are not the ones I would use now. I am fully aware that forged pistons can slap when cold. This motor slaps all the time.. Even after a 200 mile trip. The motor builder is not helping me so I am stuck. I simply will not use him again... and yes.. this is a high boost motor runnin 20-30 psi and producing 250hp per liter.

The think I just could not understand is that for years I was told that the thicker oil would minmize noise and add more cushion. At least thats what my brain decided on with the info it was given. So to see 15/50 smoke ALOT and then to see 10/30 no smoke as much and have the piston slap minimized, I thought I would post to find out why. It makes no sense to me at this point. This engine runs 25-30 psi oil press at idle and 80-100 psi at redline.

Thanks for the help and schooling!!!