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Old 09-08-2008, 07:26 PM
straydog13 straydog13 is offline
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Default fitting of piston pins/ bushings

finally got my parts back from machine shop(3 weeks)-----------anyway.
1.gapping piston ring.i just need to put it in the cyl.push it up with a piston to keep it level and measure the gap...fileing as needed going from the outside in untill i can get the correct gap....010 i beleive(will double check)-----then i should be good to go?
2.ive got a tight but easily moveable piston pin and bushing in the front cyl.a tiny tiny bit of a wobble.------the rear cyl piston pin to bushing is a small amount more.if i were to put a light oil in between i beleive i would be able to see the oil "open"...but barely.(this was a tip that was suppose to indicate that it needs to be fitted better...originated from hotrodders somehwere in the past....i can see how this is true but not sure if it applies in this case)
2a.the bushing in the rear cyl has no movement at all.seems like as long as the pin is moveing then there is no problem.there does not appear/cannot feel any scarring/gouges etc also the bushings appear to be bronze.
thanks in advance.

also---i was under the impression that pistons should match cyl.even if they are both listed as the same the cyl should be bored for a specific piston.evidently that did not happen as the pistons are not marked?----called and asked another guy(i would have used if i knew about him earlier) and he told me that the pistons are made to such a close tolerance that it is unnecasary(?)----any thoughts?
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Old 09-08-2008, 11:33 PM
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also---i was under the impression that pistons should match cyl.even if they are both listed as the same the cyl should be bored for a specific piston.evidently that did not happen as the pistons are not marked?----called and asked another guy(i would have used if i knew about him earlier) and he told me that the pistons are made to such a close tolerance that it is unnecasary(?)----any thoughts?

I have never had two pistons measure the same dimension and every set of pistons I have ever replaced had the specific piston measured, marked and bored to that specified cylinder.

In response to those who say that all pistons are manufactured to such a close tolerance that all are the same, I can only say I strongly disagree. The machine is going to run, but I am saying I believe the bore should have been done relative to a specific piston and if they are not marked then this was not done.

I do not know about you guys, but nowadays I do not buy USA made forged pistons like I once did. (Do they even have USA made pistons for sale today?)
What I buy are cast pistons, made offshore....God only knows where, and they are very, very cheap. Do you really think you are going to buy pistons of the same exact size under these conditions? If so, you are kidding yourself in my opinion..........pg
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Old 09-09-2008, 11:34 AM
straydog13 straydog13 is offline
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thats what i had always thought.what do i do now?i took the parts to a professional...paid my money.it took 3 weeks and they werent backed up...they didnt fit the rings and i found some metal shavings inside the cyl.not the end of the world but it seems very careless to me.----i hate taking anything to anyone.btw they are hd pistons.
about the pin bushing..do they seem fine to you?are they suppose to be tight?anybody have thoughts on this i would appreciate it.
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Old 09-09-2008, 06:01 PM
straydog13 straydog13 is offline
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i took my pistons and cyl to a separate local machine shop and had them measured.
pistons-3.217 and 3.2165 cyl are 3.219 which leaves a difference of 0.002 and 0.0025 and it is suppose to be 0.003 to 0.004-----------that particular shop could not hone it out further because they are not set up for bike engines but he thought it would be a good idea to help keep the heat down.the original shop is about 50 miles away and i would have leave it there because they use a traveling machinest.....that is not really an issue as i want it done right but i would like to know what others on here have to say about it.
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Old 09-09-2008, 07:06 PM
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thats what i had always thought.what do i do now?i took the parts to a professional...paid my money.it took 3 weeks and they werent backed up...they didnt fit the rings and i found some metal shavings inside the cyl.not the end of the world but it seems very careless to me.----i hate taking anything to anyone.btw they are hd pistons.
about the pin bushing..do they seem fine to you?are they suppose to be tight?anybody have thoughts on this i would appreciate it.
First of all Straydog13.........
Attached is a page from the factory manual describing the proper fitting of the pistons. I have circled pertinent parts of the text pertaining to your problem.......
Click the image to open in full size.

The factory book is 1970 to 1974. Today, everything is made with CNC machinery and much of it is made overseas. If your pistons are HD that can still mean parts come from overseas. So I would not count too heavily on the pistons being Made in the USA.

But, maybe I am wrong and all pistons made today are exactly the same perfect diameter as the ones next to it, but I would have to see the proof of that before I even considered believing it.

There is not a whole lot you can do. The bike will still run OK I am sure, but it sounds like a better job could have been done for you.
I hate these people who hold themselves out as professional and take your money then short change you on the work you paid them to do.

You can never deal with this guy again and you can tell everyone you know what kind of job he did. That is about all you can do.

You found metal shavings in the cylinders? Jeezeee.........Did you say this guy is a machinist? Machinists don't do that kind of work. Some mechanics do however.
I suggest this:
Wash the cylinders with solvent completely. Then heat up some boiling water and put Dawn dish soap in the container with the water.
Put both cylinders (one at a time of course) into the hot soapy water and scrub the bores completely with a rag. You will see the metal and grit come off on the rag. This is what would go into your engine if you had not washed the bores like this.
After the rag(s) show no more grunge, completely rinse the cylinders and dry with a towel and an air hose. Wipe some clean oil in the cylinder bores so they do not start to rust.
File the rings as needed to establish the correct end gap and assemble the engine.

Oh, the wrist pins......
Here is the fit:
A proper fit has the pin with .001 clearance with the bushing. That means the pin will have just noticeable shake in the bushing. Tighter than that and you will likely seize the pin in the bushing and/or the bushing will come loose in the rod.
To fit a new bushing installed in the rod takes a reamer. To install that bushing takes some special tools. (of course, how else would Harley have it?)
So, to address this:
2.ive got a tight but easily moveable piston pin and bushing in the front cyl.a tiny tiny bit of a wobble.------the rear cyl piston pin to bushing is a small amount more.if i were to put a light oil in between i beleive i would be able to see the oil "open"...but barely
I think the front rod and the back rod bushings are OK if....the bushings are tight in the rods.
If they are not, you will have to install rod bushings.
The wrist pins should be a nice slide fit in the bushings with just a trace of wobble. No wobble = no good. Better loose than tight here.
That is about all I can say.
This experience will show you how hard it is to find a really good motorcycle machinist. We all learn the hard way if it makes you feel any better.
Keep us posted.............pg


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Old 09-09-2008, 07:27 PM
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Quote:
Originally Posted by straydog13 View Post
i took my pistons and cyl to a separate local machine shop and had them measured.
pistons-3.217 and 3.2165 cyl are 3.219 which leaves a difference of 0.002 and 0.0025 and it is suppose to be 0.003 to 0.004-----------that particular shop could not hone it out further because they are not set up for bike engines but he thought it would be a good idea to help keep the heat down.the original shop is about 50 miles away and i would have leave it there because they use a traveling machinest.....that is not really an issue as i want it done right but i would like to know what others on here have to say about it.
I would be very careful handing them back to the same shop that did the boring. The measurements sound pretty close to what you want. I would say .003 clear is a maximum. Use your judgment here, because if they get honed too much there is no turning back..........pg
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Old 09-09-2008, 09:47 PM
straydog13 straydog13 is offline
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i will make this as quick as possible since i keep having to sign back and then have my reply deleted.
i dont beleive all pistons are made to that close of a tolerance.everything has a little difference.i understand the factory's point of view.the machine shop SHOULD make up the difference.i think its the difference between a good job and a great job.
i will live with the fit.it is close...i just didnt want any more heat problems.good is ok.i was just hoping for perfect.
the cyl's werent terrible...not filthy or a ton of metal dust or anything.looks like he cleaned and oiled them and then got careless with an airhose?????---i will clean them for sure.
ok the pins should be good.---my question is sre you saying there should no movement in the bushings???--the rear i cannot move by hand.
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Old 09-09-2008, 10:47 PM
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Quote:
Originally Posted by straydog13 View Post
my question is sre you saying there should no movement in the bushings???--the rear i cannot move by hand.
It is easy to write down a statement and have it come out with a different view on the other end of the line sometimes. That is my only complaint regarding using a computer.

The bushings have to be tight in the rods. They should not turn, rotate, or move at all. The bushings are a tight press fit into the rods.
The wrist pins should slide back and forth through the bushings with just a hint of wobble, but more of a.... 'I can feel it wobble but not see it wobble.'
pg
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Old 09-10-2008, 10:34 AM
straydog13 straydog13 is offline
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ok.i guess i need new bushings.i am going to start putting it back together asap.i would like to say i will have no more questions regarding this endeavor but i am pretty sure you wouldnt beleive me.--thanks.

i guess if put a little more thought into it i would have realized the whole point of the bushing is to keep it from wearing away at the rod.----i guess i just wanted to beleive it was good ...
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Old 09-10-2008, 10:51 AM
straydog13 straydog13 is offline
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btw i am going to find an fsm.regardless of what people say i never thought i needed it ....even with a partially restored car i never thought i needed it for it either.....but i could have used an hd fsm this time around for sure.
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Old 09-10-2008, 10:51 AM
 
 
 
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