L28 Stroker Build - I need your advice :-)

[german240]

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. 

[siteunseen]

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.

 

[german240]

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. 

[Patcon]

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?

[german240]

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! 

[madkaw]

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

Why and what new bolts are needed?

[Patcon]

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

[german240]

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, 2017 by german240

[Jason240z]

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?

[Patcon]

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...

[german240]

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

[Zed Head]

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