Is .0015" out-of-roundness too much?

[11sec_GSX]

Is .0015" out-of-roundness too much for a cylinder bore on a 6-bolt turbo motor? Cylinders 1, and 2 are out about .001" and #3 and #4 are out about .0015" in spots. The service manual says the standard is .0004" for the turbo motor and the service limit is .002" for the non-turbo motor but I can't find a service limit for the turbo motors? Thanks in advance.

 

[danl]

My manual is showing 0.0004" being the out of roundness for all 1g engines (including the 1.8L). If you think about it 0.0015 is pretty severe out of roundness for a quality rebuild.

0.002" is the specifications for deck height out of level. I like to keep this within 1 thousanths if your going to push the motor.

 

[11sec_GSX]

Thanks for the reply. I have decided to have the block bored +.020" and not take a chance with the out of roundess.

 

[GTM]

Thanks for the reply. I have decided to have the block bored +.020" and not take a chance with the out of roundess.

I don't know if DSM has what use to be know as first rebuild. These were essentially .002" oversize standard pistons and rings. However, with computer controled machining they may have eleminated the need because they can hold .0001 +/- .00005 where a machinist might have to make 3 passes to get it exact. Pistons use to be marked with their exact size and they were not always the same in each engine. But since the '80's there has been a big improvement in piston alloys and design this in part has been brought about by smog laws reducing blow-by.

I would guess with that much out of round you can't see the original hone marks on the thrust faces of the cylr walls? How many miles on this engine?

Cheers,
GTM

 

[Bostedquest]

I would guess with that much out of round you can't see the original hone marks on the thrust faces of the cylr walls? How many miles on this engine?

Cheers,
GTM

Mine was .0003 out, still had the hash marks.
The machine shop saw the marks and thought I was nuts for boring it.
I asked what is the out of round, he said .0003 which is not alot, I said factory spec limit is .0004. He went, damn those J A P engines are tight, ok .020 over it is, Oh and send me the hone sheet for the pistons.
So it was really like .026 or something like that over.

Car had approx 176K. 95K or so with a blown turbo so those miles were alot easier on the car.
And before you birate me, it was not my car, I just bought the engine from it.