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[anticgov]

It is easy if you have the equipment. But the equipment is not normally found in a normal commercial machine shop, but rather in a high performance engine rebuild shop. Back in the day (about 45 years ago) when I ran an engine build shop, we used to do this kind of stuff all the time. We had the equipment to do it.

One of the keys to hanging onto a piston is a piston vice.
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And an old one
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Then you need a Sunnen rod hone
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Thank jim, do you remember what you would charge for this job 45 years ago. I'm almost tempted to do this with my drill press. I've got some old piston to practice on first. Not sure if my drill press is accurate enough to preform this type of job.

 

[JimDawson]

Thank jim, do you remember what you would charge for this job 45 years ago.

That's a really good question, maybe $5 or so, in 1974 $$

I'm almost tempted to do this with my drill press. I've got some old piston to practice on first. Not sure if my drill press is accurate enough to preform this type of job.

Machine accuracy for the first operation is not particularly important, as long as you can set the pin hole pretty much on the spindle C/L. Then ream the hole undersize by a couple thousandths. The reamer will follow the existing hole, normally you would use a flexible reamer driver for this operation. Then hone to the final size. The honing process it really the key to make it all work, and that requires a dedicated machine, nothing else really works. Normally the clearance for a floating pin is in the 0.0002'' (0.005mm) range. Pretty hard to hit this target without the proper measuring equipment.

Then you have to machine the rod to fit the pin, basically the same process using the hone, with a tight interference fit, around 0.00075''. Then the rod is placed into a rod heater and expanded to allow a slip fit on the pin. The piston is fixtured, the rod is heated, then the pin is quickly installed in the piston and rod. You have to set the stop on the piston fixture so you don't push the pin in too far.

Easy if you have the equipment to do it, not so easy if you are not equipped. I could not do it in my shop, I would send the job down to the engine builder down the street. I'm sure there is a shop local to you that can do this. Maybe check with these guys https://hbrengines.com/

 

[tq60]

You blew out a cylinder, replacement not available?

Sent from my SM-G781V using Tapatalk

 

[anticgov]

I bought them in a rebuild kit off eBay. Haven't had much luck finding a 74mm piston with a 19mm bore hole. I bought a new crank and 2 sets of connecting rods. On one set the wrist pin hole is two big (19mm) and on the the other set the crank side is to small.

You blew out a cylinder, replacement not available?

Sent from my SM-G781V using Tapatalk

It had a lower end knock when I bought it a year ago, I noticed the old rods were out of round. So I bought a new crankshaft and rods but for some reason I kept getting the wrong rods. So the rods I ended using fit the crank but have a 19mm wrist pin bore. However the pistons in the rebuild kit have a bore hole of 17mm. So I've purchased 19mm pins to fit the 19mm rods, now I just need these pistons to have a 19mm bore hole and I can put this motor back together. It's rather frustrating every local shop I have found can't do it because they are under contract or don't have the equipment to do it. I can't imagine the job taking more than 10 minutes per piston after the machine/machines are calibrated.

 

[Liljoebrshooter]

Bush the rod end down to the smaller 17mm. I would guess any shop could do that. They change bushings and hone them to size every day.
Joe

 

[Liljoebrshooter]

Oh, and walking into a shop and saying it should only take you 10 minutes each to do these will probably not be a good idea.
Joe

 

[brino]

@anticgov

I can't imagine the job taking more than 10 minutes per piston after the machine/machines are calibrated.

First, I am NOT volunteering to tackle this job. I do not have a good method of holding a piston, I could not hold the required tolerances, plus cross-border shipping alone would be a significant cost. However, I do have a few comments.

Going from 17mm to 19mm is not practical for honing alone. That would take months!
Honing is typically done to remove machining marks from previous operations.

I believe the steps would be:
1) setup (I'd insert a 17mm pin and uses that to align to the machine centre)
2) boring from 17mm to slightly less than 19mm; likely multiple boring passes
3) reaming to 19mm
4) final honing

Machine setup definitely takes time and will be included in the final price.
Also a commercial machine shop has many other overhead costs; land rent/mortgage, machine/equipment costs, insurance, electricity, heat/AC, salaries, consumables (tool bits, lubricants), etc.

If I had to quote the job, I'd start at a full day's work for the four pistons, call it 8 hours times the going shop rate.
Then add on another 40-50% for overhead costs.
Some of the difference is that I run a home machine shop, not a specialty engine shop.
Luckily I can work at my own pace.

I am not trying to lecture, just trying to set your time and cost expectations more realistically.

Good Luck, I hope you find a place to help you.
Brian

 

[brino]

one more thing.....

I just watched the video that you referenced in post #7.
In that 10 minute video he doesn't even touch the piston wrist-pin bore.
All he has done is give himself clearance on a shoulder for the next operation of opening the bore.

So ten minutes in on the first piston and he has NOT yet started the job.......

Brian

 

[JimDawson]

Bush the rod end down to the smaller 17mm. I would guess any shop could do that. They change bushings and hone them to size every day.
Joe

In this particular engine you can't do that. The pins are captive in the rod, no cir-clips in the pistons. Bushing the rod would most likely create a failure point.

Having said that, it might be possible to machine cir-clip grooves into the pistons and let the pin float both in the rod and piston.

 

[Bone Head]

Check into using Teflon buttons instead of cir-clips.