when you have time..it's a very interesting video...yeah it's long, well worth the time though !!
... start around 3.15ish.....How one guy got his Isuzu(sp) diesel 'up and running'....
Beware of aftermarket pistons
- Thread starter Muggman
- Start date
Thanks for posting Muggman, I have learned quite a lot from this thread. Things I never knew I didn't know, the great thing about OTT.
For me I wouldn't rule out buying aftermarket parts from China, but the thread has helped me understand differences that might be unacceptable. In any event I always factor in the risk and like some say about the stockmarket, never bet what you can't afford to lose
Thanks for posting Muggman, I have learned quite a lot from this thread. Things I never knew I didn't know, the great thing about OTT.
For me I wouldn't rule out buying aftermarket parts from China, but the thread has helped me understand differences that might be unacceptable. In any event I always factor in the risk and like some say about the stockmarket, never bet what you can't afford to lose
Where I'm from beware simply means be aware, or take notice. I have learned a few things myself. Today after mic.-ing the pins and piston pin holes I didn't have enough pin hole clearence in the new bota piston and the original pin was too tight. I heated the piston with a hair dryer and retried the pin. It fit better but still too snug for a gentle press thru. I think maybe at engine temp the piston will swell even more. Ive always liked engine a little more loose than tight. The original piston was also a tap thru. NOW, I KNOW IM WRONG, but this is what I done. I took a split dowel and put some scotch bright in it. I only hit it gently and only for a couple secounds. I left it a hair tight. We're only talking one tenth or two of a thousandth. I liked this idea better than polishing the pin down. Weird thing is both the after market and the oem pins had a mini-miniscule taper it seemed. After all I've been thru with this. If I had my time to go over, I would have tried my luck at buying a used rod and piston assembly, put a 30 dollar set or rings on it, put my rod bearings in it and been running 3 weeks ago. The China piston I would have used if the rod pin had of been closer in weight. It seemed every which way I went there was another obstacle.Thanks for posting Muggman, I have learned quite a lot from this thread. Things I never knew I didn't know, the great thing about OTT.
For me I wouldn't rule out buying aftermarket parts from China, but the thread has helped me understand differences that might be unacceptable. In any event I always factor in the risk and like some say about the stockmarket, never bet what you can't afford to lose
Or copy and paste into the reply. Or use the insert image button on the toolbar.
Dan
and now we understand why aftermarket stuff is usually less expensive than oem replacement. They cut a cost somewhere. But the question is, where?
The wrist pin..... it's the big weight difference in the op chart of weights. The piston it's self isn't enough to matter. Actually non of it would have been detrimental to the engine. After all, I just watched that video of the guy cleaning up a boat anchor and running it down a river.
I am interested to know if you checked fit with the original wrist pin with the aftermarket piston? How are you deciding what is too tight, and why would you like loose tolerances? That is the exact opposite of what was beaten in my head at the machine shop. Clearances to the small side of factory spec if possible, they can only get bigger as the wear.
Also not uncommon to have to heat pistons to get the wrist pin in. They will loosen up when the engine is up to temp.
I am interested to know if you checked fit with the original wrist pin with the aftermarket piston? How are you deciding what is too tight, and why would you like loose tolerances? That is the exact opposite of what was beaten in my head at the machine shop. Clearances to the small side of factory spec if possible, they can only get bigger as the wear.
Also not uncommon to have to heat pistons to get the wrist pin in. They will loosen up when the engine is up to temp.
The factory specification for the pin is 22.002-22..011 mm
The factory specification for the piston pin bore is 22.000-22.013 mm
The allowable factory clearance is (-.011,+.011) mm = (-,0004/+0004) inch
That is an interference fit in many cases and would require heating the piston for assembly.
The coefficient of linear expansion for aluminum (.000025) is more than twice that of steel (.000011).
When the piston is heated to 200C plus in operation the piston to pin clearance increases by
22(200)(.000025 - .000011) = .062mm = .0025 inches
That results in a full floating pin and piston combination with a generous oil clearance.. You don't need or even want a free float when cold.
Dan
Yes, the original wrist pin was bigger and too tight in the aftermarket piston. I was gonna use it that way. I was always told if things are a little loose it will always run but you if it's too tight it will gall or lock up. At less than a 100 hrs a year, it will last me over 10 years and if I get a 1000 more hours out of it. In several more years it will be at someone's yard sale. The pistons are clearly made out different material compositions, so I would never know the expansion rate. I measured the after market pin at .78675 on 1 end and .78685 on the other. I measured the kubota pin at .78725 on 1 end, .78720 in the middle and .78715 on the other end. My broken piston pin hole was .7878 and .7875. I don't have the best equipment so I wouldn't bet on these measurements. I think the new piston was .7881 in the holes but it was tighter for some reason. It came down to feel, if I'm wrong I'll just be wrong. I will still have to heat the piston a little to get the pin in. On the aftermarket stuff with some oil it would drop out if you shook the piston. It may not expand though. It came with no paper work. I'm not a diesel man. I very always worked on gas engines. On a dragster it better be on the loose side or it will be broke. But longevity ain't the goal. The kubota d722 is about 44 cubic inches. Everything is so small. Sometimes you just got to do what you able to do and move on.
The pistons are an aluminum alloy of some type. You can be assured the expansion rate is 2x the pin.
Accurate absolute length measurements to tenths requires high quality instruments, regular and proper calibration, and controlled temperatures. Comparative measurements to hundredths is an entirely new big time game. Not something you can typically do in a DIY garage environment.
Dan
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North Idaho Wolfman
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Where did you get that aftermarket piston?
I've gotten several aftermarket pistons and none of them looked like that!
RCW
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There were no markings, plain brown box. I think most are made by the same manufacturer. Just labeled by the distributor. If the wrist pin had been the same weight I would have used it, but 50 more dollars I could have went oem to start with. Oem didn't come with pin, I used the original. I'm using the aftermarket rings though. I got about .012 on the top ring. About .016 on 2nd. About .012 on the oil ring. If my memory is right. I did a light hone. I got some miner visible up/down scratches, but I'm not going to go more.
