To knurl or not?

[ferox]

I am just getting started on a rebuild of my '88 Justy. My internet research shows two strongly opinionated schools of thought on knurling valve guides. So I am looking for some input on that subject. Knurling vs. Reaming & Pressing new guides. I am not into half measures, so even though I am extremely poor right now, if knurling is cheaper but substantially inferior, then I would rather wait and do it right when I have saved up more $. If knurling is inferior, but not substantially so, then I might go that route and rebuild another head later with new guides. I searched for this subject and didn't find much, so I apologize if I missed a big thread on this.

[Urabus-84HBDR]

let me ask moy brother later today, he is an auto machinist. he will know for sure. we are building my hi comp ea81 (10:1) and we are going to knurl my ea71 pistons before re-assembling the motor.

hope this helps you a little.

 

 

I am just getting started on a rebuild of my '88 Justy. My internet research shows two strongly opinionated schools of thought on knurling valve guides. So I am looking for some input on that subject. Knurling vs. Reaming & Pressing new guides. I am not into half measures, so even though I am extremely poor right now, if knurling is cheaper but substantially inferior, then I would rather wait and do it right when I have saved up more $. If knurling is inferior, but not substantially so, then I might go that route and rebuild another head later with new guides. I searched for this subject and didn't find much, so I apologize if I missed a big thread on this.

[Reveeen]

(*knowing nothing about Justy engines*)

 

It would depend on the type of valve seal you are fitting. Without a, well, radical attempt at oil control (double clip teflon valve seals, like a Crane seal, or a seal found in a Chev Vega), knurling the valve guides will provide more than ample lubrication to the valve stem/guide, ample to the point of blue smoking, excessive oil consumption, in short guide/overhead cam motors.

 

Though more expensive, though I can't *see* it being a whole lot more on a 3 cylinder engine, I would go for guide replacement.

[Nug]

Knurling involves twisting a special threaded tool into the guide. The tool does not have a cutting edge, so threads are not cut, but rather pressed into the guide. The result is a hole that is actually smaller in diameter than before. A reamer is then run through the hole to bring the diameter back to original specifications. Knurling can be used on a moderately worn valve guide to tighten it up. It will not bring back a substantially worn guide. Knurling does have one distinct advantage: The threads formed in the guide will carry motor oil, keeping the guide better lubricated than it was before.

 

Sometimes new replacement guides have oil threads that already exist. These are probably the best ones.

 

I'd say that if your valve guides are only a few thousands out of spec, then knurling them would be cost effective and a quality repair.

[ferox]

Thanks for the input. That gives me better info to talk to the shop with. I am going to get a second engine from the yard at some point so I can rebuild and swap as needed. It sounds like knurling could be a good option if the guides are only slightly worn. Luckily the head is actually accessible on the Justy without pulling the engine, so I can pull it pretty easily and swap if the thing starts smoking. Thanks again.