je piston advise...ow much clearance!

[The yob]

hi all

Again after more advise! my new forged je pistons ave just turned up and im very very supprised looking at the piston to wall clearance required, my pistons are 2618 material, it says i should run .0035-.0045 piston to wall clearance ,plus .0010-.0015 for forced induction engines(which will be) this seems alot!, im sue je cant be wrong, but just wantd to know peoples thoughts on this? think my engine will sound like a bean in a baked bean can when cold!

many thanks

[falcemob]

Don't forget that you want a loose fit for a racing engine so it may not be as bad as it seems. My mate has his engine bored and ground to the absolute maximum limits for the piston and bearing sizes, so much so that he has virtualy no oil pressure at tickover when the engine is hot.

[MotorPsycho]

low oil pressure due to wrong weight oil or excessive bearing clearances can't be a good thing

Edited by MotorPsycho on Monday 14th April 20:04

[redvictor]

The yob said:

think my engine will sound like a bean in a baked bean can when cold!

many thanks

yep,that's about right.... 2618 is high in silicon and the rate of expansion is a lot more than cast/hypereutectic pistons,particularly when you're beating up on the motor.
You are beating it right? You must be if you're putting these pistons in.You wouldn't be installing them because "it's the racing thing to do"?

[The yob]

hi

nope....ill be beating as hard as i can! tis a blown methonal injected job......or it will be within the next month!...at the min...its a pile of bits!

[falcemob]

MotorPsycho said:

low oil pressure due to wrong weight oil or excessive bearing clearances can't be a good thing

Edited by MotorPsycho on Monday 14th April 20:04

Correct but I didn't say wrong oil or excesive clearances.

[MotorPsycho]

if its got virtually no pressure at idle when warm then one of them is wrong (depends what you define as virtually none)

[redvictor]

The yob said:

hi

nope....ill be beating as hard as i can! tis a blown methonal injected job......or it will be within the next month!...at the min...its a pile of bits!

that's ok then..... Carry on.

[Boosted LS1]

.007-.007" is fine and it won't rattle either. Most of the pistons I use run that clearance quite happily.

[KP1]

It also depends on what size of bore it is, bigger bore needs more clearance. I´m bulding a 598" Chevy street engine with 4.600 bore for a customer and JE recommended 0.005 clearance without nitrous,blower or turbo.
And when you use a blower and methanol I´m sure that you cant hear any piston clearance at all...

Edited by KP1 on Thursday 24th April 22:38

[BennettRacing]

what is your bore size?

Edited by BennettRacing on Friday 25th April 11:55

[The yob]

hi

Standard bore...4.000

Thanks

[GTXJIM]

I thought the general rule of thumb was 10 thou per inch of bore i.e 4.000 inch bore 0.040 clearance

[KP1]

Depends on what the engine is built for. Street,race,nitrous,blower,turbo...
I think JE is smart enough to know what clearance to be used with theirs pistons.

Edited by KP1 on Friday 25th April 20:27

Edited by KP1 on Friday 25th April 20:30

[Boosted LS1]

GTXJIM said:

I thought the general rule of thumb was 10 thou per inch of bore i.e 4.000 inch bore 0.040 clearance

You might want to rethink that a bit or move the decimal point sideways

[KP1]

Here is JE:s recommendations for 2618 low-silicon aerospace aluminum alloy:
BORE RANGE MINIMUM CLEARENCE
2.500-3.625" .0030-.0035
3.626-3.999" .0035-.0040
4.000-4.200" .0035-.0045
4.200-4.600" .0040-.0050

RING CLERANCE
Minimum gap per inch of bore.
APPLICATION-------------TOP RING---2nd RING
High-Perf.Street/Strip----.0045-----.0050
Street Nitrous/Turbo-----.0050-----.0055
Circle Track/Dragrace----.0055-----.0057
Nitrous Race Only--------.0070-----.0073
Blown Race Only---------.0060-----.0063

example: Blown Race Top Ring 4.000 bore x .0060 = .024 min.gap
Blown Race 2nd ring 4.000 x .0063 = .0252 min.gap

Edited by KP1 on Saturday 26th April 08:08

Edited by KP1 on Saturday 26th April 08:11

Edited by KP1 on Saturday 26th April 08:14