Piston "Rock"

[Rabbi]

My friend called me up today after pulling his motor for a rebuild. He went ahead and installed his rings/pistons and new bearings.

He has never built a dsm engine before, Only Chevy's.

Well he wanted me to come take a look at his new engine, He has JE Pistons / eagle rods and some off brand ring setup.

I noticed something about his motor, Before he had his crank put in, I Couldrock the pistons side to side in the bore, I Would push down on the left or right of the piston and it would sort of "Rock" in the bore.

What would cause this? I'm assuming piston-wall clearances are not correct. Is this normal without a crank installed? I Do not remember my pistons doing this, But i was also very very anal about my clearances.

 

[JusMX141]

Forged pistons need more room to expand and contract than standard cast pistons do.

Thinking back to my Motocross days and the thousands of Wiseco pistons I installed in my race bikes...even when brand new, the Wiseco pistons would make MUCH more noise at cold start-up than a stock cast piston. This noise would all but disappear once the engine was at operating temp.

With that theory in mind- unless his Chevy's were using forged pistons, there will be noticeably more distance between a 4G63 piston and the cylinder wall than on a 350 V8 with cast pistons.

 

[kicknurass4fun]

The only way to tell is if you were to measure the piston clearance. Depending on the piston manufacturer the clearance should be around .005-.006 inches with forged pistons. The pistons are tapered from the bottom of the skirt to the top of the piston, so looking at the piston installed from the top makes it look like there is a lot of piston clearance and allows you to move the top of the piston from side to side. The true measurement comes from the bottom of the pistons skirt (widest point on the piston) measured with the bore of the cylinder wall. Hope this helps.

 

[PieEyedPiper]

Plus JE's are famous for piston slap. Less ideal for a DD but fine and dandy for track use etc.

 

[Rabbi]

So he will just have piston slap? Any real problems with that other than the noise?

He's also discussed going with different pistons now,Since he wants to eliminate the possiblity of extra engine noise.


I Myself run these exact same pistons, But i have zero slap. But i also did not have the side to side piston play that he did.


Is it something to worry about?

 

[T is for TURBO]

After I eat dinner I will go out side and check mine. I just got my short block back from AMS and it has forged pistons. Ill let you know sometime tonight.

 

[2gAWDTalon]

Run it loose fo da boost!
it all depends on the PWC as mentioned. The JE's need to be a lil looser, They expand more than Weiscos.
I have ran both and Have JE's now. I am thinking Wiesco HDs when these get put up or shut up.

 

[T is for TURBO]

My Ross pistons are tight. Zero play.

 

[Kevin Jewer]

I've never had a motor built to take any power that I couldn't move the pistons side to side on. You can easily see a few thousands play, and it looks like more than you think it would.

 

[spinz4]

My Ross pistons are tight. Zero play.

From stock to after market they slide side to side....If your's don't remove them and have all the clearances checked.

 

[T is for TURBO]

From stock to after market they slide side to side....If your's don't remove them and have all the clearances checked.

No offence buddy, but it was build by AMS. I think they know how to check clearances.

95GSXracer; what do you mean side to side? along the crank shaft, or rocking on the wristpin?

 

[Kevin Jewer]

I was thinking rocking on the wristpin, but it should move in all directions.

 

[T is for TURBO]

Hmm. Well, I don't have any. (didn't check side to side yet, but they don't rock on the pin)
But, I don't really see the advantage of haveing that much play. I understand that forged internals expand and contract at different rates and percentages compared to the cast iron block, so they need a little more room, but mine are in snug. Granted I did have to go .020 over on the cylinder walls, so maybe the oversized rings have somthing to do with it.

 

[Kevin Jewer]

As I said before, you can see a few thousandths movement more easily than you might think, which is perfectly normal piston to wall clearance. My current motor is very loose in comparison since it was built to run a lot on nitrous on top of a lot of boost, the pistons move so much in the block it's almost scary. It's probably only about double the clearance of a typical street/strip motor though.

I'm not sure why you can see movement in yours, probably just not pushing hard enough. In either case, there's nothing to worry or debate about. All that matters is that the clearances are correct for the parts you are using and the intended use of the motor as measured by something more accurate than your eyeballs.

 

[T is for TURBO]

As I said before, you can see a few thousandths movement more easily than you might think, which is perfectly normal piston to wall clearance. My current motor is very loose in comparison since it was built to run a lot on nitrous on top of a lot of boost, the pistons move so much in the block it's almost scary. It's probably only about double the clearance of a typical street/strip motor though.

I'm not sure why you can see movement in yours, probably just not pushing hard enough. In either case, there's nothing to worry or debate about. All that matters is that the clearances are correct for the parts you are using and the intended use of the motor as measured by something more accurate than your eyeballs.

are you saying my eyeballs aren't an accurate form of measurement? maybe thats why my shoes dont fit

but really, ill agree with that

 

[Rabbi]

Well my buddy ended up buying a set of wiseco pistons so I'm getting a spare set of JE's for free because he thinks they are defective!

I Told him they are fine, But he wouldn't listen. Oh well i got free backups =)

 

[spinz4]

No offence buddy, but it was build by AMS. I think they know how to check clearances.

95GSXracer; what do you mean side to side? along the crank shaft, or rocking on the wristpin?

Voted to wiseman!

I don't care who built your motor.....I build my motors and have done so for more than a decade. You sir =