Bad news. I talked to an experienced engine builder. I told him that I only measured 1 piston ring gap (I seriously don't understand why I did this). He strongly recommended to start over, and that's what I am going to do

..first engine, lesson learnt! I just hope that I won't run into any issues with reusing the head and rod bolts. 

Awe man, bummer.  When I tore my head gasket and had to pull the head off my newly rebuilt motor the forum said that since the head bolts hadn't been through a heat cycle they should be fine to re-use.  That was two years ago and no issues since.

 

A friend of mine just checked his piston ring gaps. He got exactly the same  rings+pistons, same bore (same engine shop), all gaps were within spec (on the tight side, though). It is very unlikely that my gaps would be any different... However, I might still tear it all down again. Let's see. 

1 hour ago, german240 said:

A friend of mine just checked his piston ring gaps. He got exactly the same  rings+pistons, same bore (same engine shop), all gaps were within spec (on the tight side, though). It is very unlikely that my gaps would be any different... However, I might still tear it all down again. Let's see. 

In theory they will all be the same but sometimes cylinders vary a little bit after honing. It's cheap insurance while the motor is out to go ahead and check them all. Do you have a bore gauge to check run out?

I wouldn't say it's cheap.. All new gaskets, new bolts and a lot of time. My friend  had exactly the same ring gaps all around, no variance at all. But you still are right! 

Unfortunately you can’t take that for granted that all the rings are the same. 

Why and what new bolts are needed?

I would reuse everything gaskets, bolts, etc. The time is cheap compared to destroying a freshly rebuilt engine

The question is: What are correct ring gap specs for this application? It is not a KA24E engine (where the pistons are from), nor a stock L28.

NPR (Japan ring manufacturer) lists the following ring gaps:

I'm still undecided

@madkaw are you sure that the head bolts (got new OEM turbo bolts) are not a yield type?

Edited December 8, 20177 yr by german240

7 hours ago, german240 said:

The question is: What are correct ring gap specs for this application? It is not a KA24E engine (where the pistons are from), nor a stock L28.

NPR (Japan ring manufacturer) lists the following ring gaps:

I'm still undecided

@madkaw are you sure that the head bolts (got new OEM turbo bolts) are not a yield type?

you'd gap the rings for the pistons, so surely you'd gap as per ka24e engine specs/manual?

I would think you would gap per the ring manufacturer specs like the ones you listed based on the piston they're on. I would think ring position relative to combustion and the size of the groove in the piston is the overriding factor not the block they are mounted in. I would think a flame front is a flame front. I suspect compression has more effect on the rings than what the engine is...

Piston and piston ring gap are totally independent. It all depends on ring material and block material as only the difference in thermal expansion is relevant. That's why I won't find a perfect answer, realised this today

Those are wide spec ranges.  Builders tend to open the gap if they expect a hot running engine.  Even if you had stock pistons you'd probably still not have a clear answer.  Those KA pistons aren't that much different from stock, and you don't have a turbo or anything special.  Just avoid the small number and you'll probably be fine.

Another interesting topic that we can spend lots of time on though.  Thanks.

http://www.acl.co.nz/wp-content/uploads/4-Compression-Ring-Gaps-For-High-Performance-Engines.pdf