Vitara Pistons too sloppy? what about trying this?
 

Hey,
My little brother is going to school and getting his ASE certificate, but he came home today and told me about a process that some hotrodders use on their pistons to take up a little piston wall clearance. The process involves lightly knurling a small portion on the face of the piston skirt (exhaust/intake). He was told that pretty much any machine shop can do this.

I also read a little bit about it in his engine rebuilding book. I think this might be an alternative to taking up a little "slack" in the Vitara pistons. If i ever have to rebuild my current motor i'm gonna try this out.

EDIT: according to some research, knurling can increase the piston diameter by a "few thousands," which would be perfect on some vitaras.

Sure, there are those who are totally against this technique and there are those who say that there are increased benefits of oil retention and slight cooling.

Just a thought... discuss away...

Re: Vitara Pistons too sloppy? what about trying this?
 

Old hotrodders indeed.

Still, if you can do it why not?

Re: Vitara Pistons too sloppy? what about trying this?
 

I guess another question would be how much it would cost to get the process done.

Re: Vitara Pistons too sloppy? what about trying this?
 

If you are rockn' Vitaras you are cheap, and labor isn't. So I can't see that we are moving in the right direction here. They are proven to make power and be reliable, so this seems to be a moot point.

Re: Vitara Pistons too sloppy? what about trying this?
 

I had a machine shop knurl a set of srp's along time ago, i think it was like 20 dollars.. definatly some backyard ----.

Re: Vitara Pistons too sloppy? what about trying this?
 

Have you actually checked the p2w clearance on your pistons and cylinders? We are running a set of stock bore Vitaras in one of Bambi's old A6 blocks, and they were just fine, no slap, no knock, sounds normal.

Just make sure you don't spend more trying to make somthing work, than you would have spent on a sure thing.

Craig

Re: Vitara Pistons too sloppy? what about trying this?
 

I know my current build has a little slop, a little noisy when cold, but i just thought it would be an idea for those who are concerned with the piston/wall gap.

Re: Vitara Pistons too sloppy? what about trying this?
 

this brings up a problem that i have with my build. the machine shop measured the block that im using and said that std bore pistons will work but that its going to be on the loose side. would this help out ?

Re: Vitara Pistons too sloppy? what about trying this?
 

i would say try that ----...i dont see it hurting anything really...and if you have a significant amount of slop your probably fucked anyway...might as well try it for like 20 bucks if thats what the price is

Re: Vitara Pistons too sloppy? what about trying this?
 

So what's involved in the process? I've never heard of it before.

Re: Vitara Pistons too sloppy? what about trying this?
 

Throwing the pistons in a vise and squishing the pistons around

Re: Vitara Pistons too sloppy? what about trying this?
 

$20 to put pistons in a vice? lol...

The pictures in my brother's book looks something like this. I'm sure machine shops have some special tool.... vice?
http://www.timgilles.com/photogaller...rledpiston.jpg



EDIT: Heres another pic i found of a Honda motorcycle piston. http://teamhansenhonda.com/parts/photo025.jpg

Re: Vitara Pistons too sloppy? what about trying this?
 

nah, I dont know if thats how they do it.. I just always joked that they did it because the marks look so similar. ;)

Re: Vitara Pistons too sloppy? what about trying this?
 

You put them in a lathe and use a knurling tool it has little rollers with various patterns that cut.That is def old school and used mainly in Cuba etc these days.

Re: Vitara Pistons too sloppy? what about trying this?
 

how much slop is it. you can't build a motor by saying. eh that feels a little loose, you need to measure

Re: Vitara Pistons too sloppy? what about trying this?
 

i should know by tomorrow but if not, monday for sure. ill post back when i know.

Re: Vitara Pistons too sloppy? what about trying this?
 

Talked to my boss (automotive machinist) about this today. I asked about the process, and he was like, where'd you read that? That's OLD news. He said back about 40 years ago, people used to do it because leaded gasoline helped the cyl's wear away more quickly. Doing this allowed the owner to run the block with a quick hone and re-ring, instead of a bore/hone job costing a bit more money and time. This was typically done on pistons with a full 360* skirt, not today's style skirt design, although it's possible to do.

He was sort of shocked that people were still talking about this process, since he was around rebuilding motors when they realized it was really not a good thing. He told me that I should stay away from this.

-josh-

Re: Vitara Pistons too sloppy? what about trying this?
 

Re: Vitara Pistons too sloppy? what about trying this?
 

yeah, I can see doing this on simpler older motors that hot rodders and such used to but I just don't know if I would trust knurled pistons in a modern motor.

like 90dx said, knurling is done on a lathe. It doesn't really cut any of the metal away, it actually forms or presses it to fit the shape of the knurling tool, although you do get some small shavings that come off on the tool bit. It's fairly easy to do if you have a good lathe and knurling tool.

http://www.technologystudent.com/images2/knurl3.gif

That's basic knurling in a nutshell

Re: Vitara Pistons too sloppy? what about trying this?
 

I did some knurling on some tools like a bearing puller i made etc and it is great for grip but i sure as ---- would not do it to a piston for a boosted motor.Knurling is def simple so if you wanted to try it the cost shouldnt be much it would probably be one hours labour say $50 roughly.

Re: Vitara Pistons too sloppy? what about trying this?
 

narley

Re: Vitara Pistons too sloppy? what about trying this?
 

Knurling is so simple buk could do it. It's the knurling attachment that costs money.

Re: Vitara Pistons too sloppy? what about trying this?
 

my p2w clearance was .004 i didnt think it was that bad...its just barely out of service limits, mine didnt knock too bad, nothing more than any other forged piston...i had a friend with cp's in his sohc and you couldnt tell the difference.

Re: Vitara Pistons too sloppy? what about trying this?
 

So this doesn't scratch the cylinder walls? I would think that since the skirts aren't really smooth anymore then it would be easy to develop scratches on the walls that could cause a whole list of problems.

Re: Vitara Pistons too sloppy? what about trying this?
 

Aluminum is softer than steel.

Re: Vitara Pistons too sloppy? what about trying this?
 

this dude is right....its the lathe...same way you would make a handle for a cheater bar or something like that....very simple...i dont know how effective it would be exactly cause your really not gaining much as far as diameter...atleast you wouldnt think

Re: Vitara Pistons too sloppy? what about trying this?
 

A few thousandths is a few thousandths.

Clean bore D16 - a hard find, they are all 7+ years old now - take STD Vitaras as noted, but the ones with a little wear on the bore are the slappers. Frankly, the guys running Vitaras to be cool and only making 250-275 aren't going to have aproblem with this, but try running a big power D16 with piss ass piston-wall clearances and see how long it is before you run into problems.