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#341350 - 11/04/10 6:20 am REAMING WRIST PIN BUSHING
Bob G Offline
BritBike Forum member

Registered: 07/13/07
Posts: 445
Loc: redondo beach, ca
Is an adjustable hand reamer ok for sizing the wrist pin bushing? Or is their a better tool for the home mechanic? I would like to avoid a trip to the machine shop if possible.
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#341357 - 11/04/10 8:20 am Re: REAMING WRIST PIN BUSHING [Re: Bob G]
Tiger Offline
BritBike Forum member

Registered: 10/26/04
Posts: 4429
Loc: Melbourne Australia
Old Phil Irvig used to recommend the use of a "planishing broach" for that job.

I think his main concern was smearing of the bush surface which would destroy porosity.

Make sure the reamer is sharp and do not rotate the thing backward ?
_________________________
1969 TR6R
7.62 x 51 is not a maths puzzle.

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#341364 - 11/04/10 9:27 am Re: REAMING WRIST PIN BUSHING [Re: Bob G]
twinspin Offline
BritBike Forum member

Registered: 11/06/05
Posts: 721
Loc: Berkshire
From what I've seen in another recent thread, a ruined engine may have been caused by poor alignment/reaming of small end bushes. Unless you have the facilities get an experienced machine shop to tackle it. Worth checking recent threads as clearance is also an issue. I wish I knew how to post links to other posts here.


Edited by twinspin (11/04/10 10:15 am)
_________________________
1971 T100R
1970 T120

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#341382 - 11/04/10 12:38 pm Re: REAMING WRIST PIN BUSHING [Re: Bob G]
649 Offline
BritBike Forum member

Registered: 07/25/07
Posts: 594
Loc: australia

Engine Blow UP 1970 T100S

read that thread, and keep in mind John Healy knows what he's talking about
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1970 tr6r dryframe

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#341388 - 11/04/10 2:00 pm Re: REAMING WRIST PIN BUSHING [Re: Bob G]
John Healy Offline


Registered: 03/24/05
Posts: 8575
Loc: Boston, Massachusetts
A planishing broach is a series of increasingly larger smooth round rings on a bar that is pulled through the bushing. May I quote from Broaching Practice by Edward K. Hammond.

Originally Posted By: from hammond's book
SIZING ROUND HOLES with a Planishing Broach Fig. 6 show how a broaching machine and planishing broach were used for sizing holes in hard phosphor-bronze bushings. This material, as any mechanic who has had any experience with it knows, is difficult to finish-ream. It is tough, elastic and slipery, and the less there is to ream the more difficult becomes the operation. Instead of reaming, the holes are enlarged slightly by pulling a smooth-toot broach through in a regular broaching machine. It will at once be seen that the operation is that of compressing the metal in the sides of the hole until it has enlarged to the finish size. Each of the rounded rings or beads on the broach is a little larger than its predecessor, thus gradually compressing the metal the desired amount.

Full text at
http://books.google.com/books?id=a5pKAAA...ach&f=false

This is a similar process Carrillo uses on there steel rods to finish the bronze bushing used in their connecting rods. Sunnen also has a process that adapts their pin hones to burnish wrist pin bushings to size.

But the most common way these phosphorus bronze bushings are sized is with a Sunnen connecting rod hone. Because, unlike a steel rod that can be bent to insure the centerline of the bushing is aligned with the rod's big-end, aluminum rods must be machined square during the refurbishing process. You cannot bend an aluminum rod to align the bushing!!

Because of the nature of most bronzes used for this application they are hard to machine using any form of cutting tool. A reamer, especially a fragile adjustable one, is no exception. And as said above, don't turn the reamer backwards when reaming one of these bronzes or in an instant it will no longer have a cutting edge. It will have to be re-sharpened before it will cut again.

Because of this Triumph always provided the replacement bushings to a finished size - pre-finished. An allowance was made to the bore so when installed the pressure of the press fit crushed the bushing to it finished size. While not a perfect solution, it is a lot better than trying to ream the hole with an adjustable reamer. For a lot of reasons none of the current group of people manufacturing replacement bushings supply them pre-finished.

In short, just because you can buy replacement bushings doesn't mean that you are qualified to install them. This is not a home-workshop job and should be left to a professional. I dare say that few motorcycle shops have the training, equipment to do the job, or the ability or equipment to check their work.

When the bushing is not square to the centerline of the crankshaft bearing you not only cock the piston left to right, you create a little mechanical engine. This little engine drives the wrist pin from one side to the other with each time the rod changes direction. It does this with enough force to cause the circlip to fail allowing the pin to cut grooves in the cylinder. Of course the cocked piston does nothing to help oil control, detonation and the other horrors we see with pistons.
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#341461 - 11/04/10 10:00 pm Re: REAMING WRIST PIN BUSHING [Re: Bob G]
Bob G Offline
BritBike Forum member

Registered: 07/13/07
Posts: 445
Loc: redondo beach, ca
Thanks once again for all the invaluable info. I will be taking them to the machine shop. I read the T100 engine blow up string and it made me very nervous. I have already pressed in the new JRC wrist pin bushing using a hydraulic shop press. I will have the machine shop make sure it is square.

As a side note. I just started working at a small shop that specializes in old BMWs. They have a really slick tool that installs a new wrist pin bushing while pushing out the old one using a guide to keep it square.

You then use the tool to push a big ball bearing through the bushing to get the correct size. Which I guess is like broaching.
I thought about trying to adapt it for Triumphs, but so far I have not been able to locate the proper size ball.
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Bob Gregor

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#341463 - 11/04/10 10:35 pm Re: REAMING WRIST PIN BUSHING [Re: Bob G]
Bob G Offline
BritBike Forum member

Registered: 07/13/07
Posts: 445
Loc: redondo beach, ca
I had also thought about pushing an 11/16 (.6875) ball bearing through the bushing and finishing off the last 1 to 2 thou with a fixed size precision hand reamer or ball hone.
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#341470 - 11/04/10 11:33 pm Re: REAMING WRIST PIN BUSHING [Re: Bob G]
John Healy Offline


Registered: 03/24/05
Posts: 8575
Loc: Boston, Massachusetts
Good Bob... This is important and almost universally overlooked, even by what are called professionals in this old bike trade.

Remember the BMW has a steel rod. This allows it to be straightened. It is different technology. Also in true German engineering the crankcase mouth will be square to the crankshaft, something seldom seen on an old British twin. This allows you to use two parallels to check the pin to see if it is square to the crankshaft.

In most modern automotive machine shops straightening steel rods is considered "old school" or something they did when dinosaurs roamed the world. You will still find the odd shop that still uses this practice. Especially if they work on old Harley's or the like. In a modern shop, more often than not, the bushing will be honed or bored using a purpose built machine designed to get all of the dimensions correct.

While you could use a ball of the proper size to get the finish dimension, you would want it to provide the finish dimension without the need to do any more machining (we supply a 7/8" ball used to size the timing side camshaft bushing).

The last thing you would want to do is leave a couple of thousandths to remove, unless you were going to hone it. The metal these bushes should be made from are hard to machine using a reamer or single point tool. This is especially true when you are taking a light cut as the tool tends to chatter. This material also dull these types of tools very, very quickly.

A ball hone is absolutely out of the question as there is no way to keep the hole straight or keep it from becoming bell mouthed.


Straightening Harley, etc. Rods:

Straightening Harley Rods
Popular Mechanics explains rod straightening
_________________________
"Don't just teach your children to read. Teach them to question what they read." George Carlin

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#341493 - 11/05/10 3:03 am Re: REAMING WRIST PIN BUSHING [Re: John Healy]
Bob G Offline
BritBike Forum member

Registered: 07/13/07
Posts: 445
Loc: redondo beach, ca
I could use a 17.5 mm ball if I can find one. That would give me the exact dimension. But from what I am understanding, the Sunnen conrod hone aligns with the big end of the rod, keeping everything parallel and/or slightly correcting misalignments.

And it is better to go with .001" clearance then with .0005" to help compensate a tad more for bad machining?
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Bob Gregor

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