the shop honing my ~10k mile old 96mm cylinders is telling me the brand new pistons are going to be loose in the cylinders! WTF, the original KB set of p/c's is what was in the original engine. I've been planning re-honing the cylinders and using a new set of KB pisons w/new rings...

WHY does God hate me? Is boring out 93mm or 94mm pistons & maatching them up to the pistons the only way to go?

HELP!!!

Dumb question.

Can you get Oversized Rings for them?

I dunno but don't think so. Probablly want the rings holding the compression as little as possible.

Anyone else know?

-pt

Bad idea. Piston to cylinder clearance is important.

PM me if you end up needing a set of cylinders to re-bore.

Perhaps the cylinders were too large the first time around, so now they're even bigger?

That is what I was afraid of... This is only for a street car. Jake thought the old cylinders should be OK but just need rehoned. Then again he's also said the cylinders that come w/the KB p/c set were not very good to begin with.

McMark - I may take you up on the offer. I'll take a look at the set when I pick it up tomorrow. The shop has been around for 20+yrs and I tend to trust their judgement (KOS Motorcars in Lyndhurst, NJ).

I'm PISSED b/c after a 2 week delay I thought this w'end I'd be able to get the damn engine together & the car back on the road.

Have Mark send them to Rimco (in CA) for boring. Measure the slugs first before they bore.

I'm just amazed that the almost new (only 10k miles) cylinders that came w/the pistons as a MATCHED SET (from Keith Black ) are already shot. They should require a simple honing fore reuse w/a new set of pistons.

But since when does "should" mean "is"...

-pt

Keith Black doesn't make cylinders.

Where did you buy the set up from??

Our spec for skirt clearance is .0018-.0030 at max. Looser than .003 with KBs and they'll rattle and burn oil

I'd have to dig up the receipt but I bought them ~ 4yrs ago from a place out in California. From memory, they were advertised as a set and the pistons were the genuine article - same as the ones you sell (and just sold me last week...). It is possible the jugs were inferior quality.

BTW, Thanks for the skirt clearance #'s. I'll find out later this morning from the shop what readings they are getting w/the micrometer.

-pt

Yep- They are made in Mexico

Now you see why saving a buck initially isn't really "saving a buck" in the end.

The issue is that the cylinders were not made specifically for the KBS when they were honed- all the off the shelf kits I found were too large for the KB piston. Most KB pistons measure 3.77780 and most of those Mexican cylinders start off at 3.7805 at minimum giving loose clearances from the beginning for the KBs.

The other fact is that in 10K miles they can wear enough to be out of spec, they guy that made them only got paid 5 bucks a day for doing the job, so you can't ask for too much!

I quit selling them, they are still listed on the site, but thats just because I keep forgetting to remove them.

We've learned a lot in the last 4yrs... Thx again for sharing your info Jake.

-pt

Unfortunately the guys selling those parts haven't leaned in the last 4 years that they are junk! either that, or they just don't care!

I'm not recommending this at all since I have no experiance with it, but in one engine rebuild book I had thumbed thru, they mentioned knurling the pistons to bring them back to spec.

I just learned a new word

glad to have helped

here is more on the process....knurling

Knurling

Pretty cool process. Makes for a nice grip on a hammer or screw driver.

I know your not recommending the process. I just want to second the motion to not knurl. I cant see how it could be good. I can see how it would raise the surface and I also could see how it would make it rough. The process pushes the material out of the way. I actually would like to know more. Who, how and results.

I'm going to agree with Jake when he said - Now you see why saving a buck initially isn't really "saving a buck" in the end." I'm not saying dump crazy money into the engine. It's a learning process. Pete and his father have a good approach to working on their 914's. I like them am learning by working on this engine.

Ahh I see in your link

That's the problem with "cheap" parts.

They don't care and will blame the builder for the failure.

Yeah, 4yrs ago when I bought them there wasn't the same depth of research available as there is today. I'll likely be boring out 94mm cylinders to get the skirt clearance within acceptable range.

So, this engine will be ready by, say, Fall 2007.....

The skirt clearance ended up being within range. That was good news. The mechanic was looking at the gap between the crown of the piston and the cylinder. For some reason, the KB's measured ~ 95mm at the crown of the poston, and ~ 96mm at the skirt.

I guess thats just the way the KB's are...

This is interesting! Out of curiosity, I just measured a piston and cylinder that is out of an old 2.0 . I always thought that pistons were made intentionaly out of round. I measured 3.767" ROUND (not ovaled) at the top of the piston. I measured 3.697 at the skirt. That is a .021" difference! My cylinder measured 3.702 throughout. Using the skirt measurement I get .005" clearance. I assume this means that I cannot hone and reuse them. Is this correct or is the .003" more for the KB's and not Porsche pistons?

Mark

I'll defer to the experts on this one...

-pt

I *think* my 911 J&Es (and some V8 pistons) were made w/ the top smaller than the skirt. The top takes the most heat and thus expands more (esp w/ turbos). The skirts run much cooler and can run closer tolerances. Been ages though...

SMD