1JZ Allowable cylinder wear

I have a 1JZ block that has supposedly been to a machine shop prior to purchasing, I am looking at buying a new set of pistons and have measured the cylinders between 86.03 - 0.04 with a micrometer and bore gauge

My concern is the wall clearance with a 86.00 (STD) size CP Carrillo piston, are my bores a little too loose or will this be okay? I cant seem to find how much clearance is machined into these pistons and what is allowable

Any help much appreciated!

Pistons are normally manufactured with the correct clearances for a standard/nominal bore.

Depending on your application, and how much heat you're putting into the piston, more material may be removed from the bore to give the recommended clearance for, usually, high boost levels where the piston may be expected to expand a little more.

In your case, there appears to be a bore "oversize" of 1.2-1.6 thou'", and that woul seem to be well within the "re-ring" tolerance, and so 'should' be fine.

However, I'm not a "JZ" chap, and those more experienced with the engine should be better able to advise with the boost/power levels you expect from the engine.

Also, that bore finish is looking rather coarse, much rougher than I'd expect from a properly honed/finished bore, but that might just be down to the photograph?

Thanks for the fast reply and information

It is difficult to tell in photos as I tried to get the best focus/lighting to show the hone pattern, It doesn't feel insanely course to touch but then again Im not an experienced builder so hard to know where the line is.

There are not any marks I can feel with a finger nail just some visually, Ive uploaded a few more photos if this helps your judgement

From my experience you are in very tricky situation, and here is why- CP usually makes their pistons with 0.09 mm PTW clearance for JZ when the bore is done to the spec. Having the bore 0.03-0.04 mm extra size makes it total clearance of 0.12-0.13mm which is a bit too much but provides absolutely safe clearance number which is safe for any amount of boost or temperature. We never had a single issue with any jz engine since started making that PTW clearance. The tricky side of that is once you will install new piston rings with proper heat expansion clearance it may also chew off 0.01-0.02mm of bore size while breaking in... So you might end up with 0.14-0.15mm gap after all. That could be a problem for piston rings sealing effectiveness and pistons can be a bit rocking during engine cold start...

The bottom line is -as Gord said it depends on application. If your plan is to load it very hard extra clearance should not be an issues. However for a daily car I wouldn't recommend such a big number...

PS have you used calibers when taking measure of the bore? Are you sure your 86.03 is really that number?

To me it would worth double-checking the piston size and bore size to find out actual gap size...

Im planning on a streeter/track car on E85 around the 500-600hp mark

I will double check the measurements again, I used a micrometer set to 86.00 and zeroed the bore gauge to that it was a quick measure so I could very well could be off!

I have a set of factory pistons that were in the block when purchased so I might measure from those and see what sort of clearances I see

Thanks for all the help!

I really don't like the look of those bores, not just the coarse "hone", but it doesn't even look like that on several cylinders as the 'grain' is just around the top of the bore, and there are the vertical scratches on several bores that look quite deep.

Of course budgets are always an issue, but as you're looking to buy new pistons, anyway, I'd be looking for a trustworthy machine shop* to take the bores out to the next over-size, or two, of the pistons to clean them up. That way you'd have the best possible clearance and finish.

*might be a little more expensive, short term, but there are specialist builders who will do this for you with 'plates honing to required clearance for your application, deck and align bore if needed, etc - basically giving you a 'blue printed' block that is literally better than new, other than the bore being an oversize.

Yep like you have said If im going to spend the $$ on forged pistons its worth the extra mile to ensure the cylinders are perfect

Spoke with a local machine shop and a torque plate bore/hone to 0.5mm over is a reasonable price, Looks like thats the way to go!

Thanks for the help fellas!

I'd just double check the rep' the 'shop has but if they've a JZ 'plate, I would assume they're good.

I'd also hold of in buying the pistons just in case it needs more to clean up the scratches - I expect not but...