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Discussion Starter · #1 ·
Just fitted one of the new bushes.
I`m told that the oil-way hole should be drilled after the bushes have been pulled in.
The workshop manual (and Haynes) says the gudgeon pin should be a good sliding fit, with no lateral movement.
OK fine, but it also goes on to say the bush should be reamed to 0.6890/0.6894. This rather odd size is 45/64".
The gudgeon pins are tight, should I force them in or use some very fine abrasive?
I doubt if any garage/workshop has this size reamer to borrow.
Your comments would be appreciated.
 

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heh!

upper end bushings:

they used to come with the oil hole predrilled.

a sliding fit is OK, you want there to be enough clearance for oil to get in there to lube the wrist (gudgeon, upper end, little end) pin.

they still sell, 'chuck em in an electic drill' brake cylinder hones, for small holes, some of the gang here use them to open up bushings.

drill the oil hole first, than hone.

as an alternative fresh 220 wet or dry paper used with soapy water wrapped around a dowel can work.

you really need to work at keeping the bushing hole round.

the closer the dowel size, with the paper around it, is to the existing bushing interior the easier it is to keep the honing even.

the good machinist supply houses sell expanding reamers. Heres a
used 11 piece set on ebay for $99.00-
.468 to 1.500

11 Piece Adjustable Hand Reamer Set:

http://cgi.ebay.com/MACHINIST-11-PC-ADJUSTABLE-HAND-REAMER-SET_W0QQitemZ350187316042QQcmdZViewItem
 

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Discussion Starter · #3 ·
Thankyou Sunshine Jim.
Never done this before.
The info you sent is invaluable.
So ideally, it should be reamed.
I think I will try to use the wet soapy wet and dry to begin with.
Just to keep the bore circular.
The new gudgeon pins were noticably slack in the old bearings. Not regard with the fit, but I could sense movement laterally.
After forcing the bush in, it occurs to me that the edges maybe burred.
First job., clean up the outer edges.
Hopefully a clean up will allow oil to penetrate the bush.
The man who supplied the bushes said, "I know what you are going to say, no holes"... "drill the hole after fitting the bushes". "All T120`s versions have these bushes". (70-1511)
He said nothing about the internal bore, so I assumed that they were a standard size.
Live and learn eh? Makes me wonder why they are not pre-reamed!
 

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heh!

i'm a nube here bud and just getting a handle on "unit" stuff, theres enough differences in the parts that i'm still in the learning curve eh?

But.... the old Pre-units i used to build are very similiar in some respects. I don't think upper end bushes differ at all from the early stuff.

the clearance is relative and you develop a 'feel' for a nice fit. the reason for the ream is the slight 'shrinkage' of the bushing internal dimension as a result of the 'press' fit into the rod end.

there should'nt be more than a few thou to take out of the 'ID' so go carefully till you get a nice 'slidey' fit with minimal finger pressure.

also fit and "lap" from both sides to make sure you are'nt cutting a cone shape! a common mistake when you first try this technique, i use a rolling stroke and start the pressure at the top when the rods in the engine and rotate the pressure in even divisions around the inside. stuff something in the crankcase so the bits are kept out of course, you've got bronze, water and sand paper bits dripping in the vicinity so i use a couple of layers of rags for insurance.

don't be afraid to go too far and need another bushing, this is 'poor boy' fitting and takes developing the "knack" to get it right, on the other hand it's a great skill to have in your trix box. Triumphs have been kept running by yer average bloke and his friends for almost a hundred years. welcome to the tradition!


the aluminium and bronze have a slightly higer coeffecient of expansion than the steel upper end 'pin' so a nice fit will open up ever so slightly when everything warms up.

as you get close sand less and fit more often!!! and of course you want to deburr the oil hole so any "swarf" from the drilling does'nt go wandering around in the engine.

so how do you deburr the inside of the oil hole? i build model airlanes so i always have Music Wire around.(high carbon spring steel). I just sharpen 3/16's of the end of a 4 inch piece and put a small kink on the wire that still lets it go down the drilled hole but lets it have some de-burring ability. the slightest chamfer of the inside lip is all you need, mainly you just want to clear any drill 'Swarf'. the little 'still attached bits' at the inside edge from drilling.

to de-burr the bushing itself you can use anything cone shaped (45 degress or so works fine) and larger than the hole with the 220 grit and just put in a tiny chamfer. a final light pass internally de-burrs that chamfer and "Bob's yer uncle". ; )
 

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Discussion Starter · #5 ·
On second thoughts, I think a reamer (17.5mm) is the way to go.
Today I will try to beg/borrow/buy an adjustable 21/32" - 23/32" hand reamer.
Found a supplier on the web who sells the above for about £7.50.
But really, I want to get the job done this week-end.:)
 

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Source for Wrist Pin Reamer Tool

Caulky,

This won't help you, especially if you are trying to get the job done over the weekend. However, this is the only source I found so far (in the US) that has a suitable reamer. The source is:

http://www.parkersclassics.com/

They carry the correct wrist pin reamer for $55 US, as well as a valve guide reamer for for the same price. I am sure these are common tools that available elsewhere for less, but I thought I'd throw this source in just in case you or others could use it.

Good luck.
 

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Discussion Starter · #7 ·
Thankyou all for your input.
I have managed to borrow a 21/32" to 23/32" adjustable reamer.
The instructions given were...turn it clockwise and dont stop.
Do not ever turn it anti-clockwise.
Make several light cuts until the desired size is achieved.
I think a drip of oil lubricant may be desirable.
Now to drill the oil-way and proceed.:)
 

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good score!

very nice loan!

yup,light cuts are the way to go, the advantage of the reamer is accurate parallel cutting. a 'tee" handle helps keep it true. for the first turns just try for light contact with the inside of the bushing, ease it into the cutting with light finger adjustment on the cutters with it in the bushing. If you still have the old bushings around practice on them.Let us know how you make out and the best of luck to you!
 

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l hope you have not press fitted the small end bushes in already. My mechanic tells me that you get predrilled bushes and match them to your new gudgeon pins. See Hughie Hancocks dvd for Triumph way. That way you are sure of your clearances before you press them in as depending on your method you may have just burred the ends and a full ream is not needed. He does not reccommend any kind of emery paper treatment as you cannot get a true parellel ream with paper. nor sand the pins as they are heat treated and any grit embedded in the surface will rapidly wear them. lts worth waiting for further replies before you embark on a path to rattly small ends. My bloke is a Triumph club member of 30 years so what hes says goes for me.
 

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There have been several good points made here. I dislike the idea of using emery paper for this application. you will almost certainly make the holes out of round and tapered, not to mention leaving grit embedded in the bronze. Why not ream AFTER you have drilled the oil holes ? In all probablilty you will only need to remove material where the inside bore has been deformed. ( try the fit before installing them in the rods) If you can turn the gudgeon pin inside the bearing by hand all is well. It will slacken off a little as it runs in and anyway the steel pin expands less than the bush as it heats up. The fit to the pistons used to be heat interference, ie they needed to be assembled with the piston hot and gudgeon pin cold ( drop teh pistons in hot water). they only start to move when the piston warms up.
 

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Discussion Starter · #11 ·
Thanks for your comments.
Having looked at several suppliers pictures of the bushes (70-1511), all are not pre-drilled. If you have the part number of drilled type, I would be interested to know what it is.
However, I notice in the workshop manual it says in section B27, "Centralise the new bush and tube and align the oilway in the new bush with that in the connecting rod".
Further it says,"ream the bore to the size given in `General Data`.
[0.6890/0.6894 in (17.50/17.511mm)]
If the pre-drilled bushes were available (which I doubt) and the bore was the size above, 4/10ths of a thou limit, it would be very likely that the bore is distorted/out of limits after fitting, hence the need to ream it.

The gudgeon pins were a sliding fit before pressing the bush into the conrod, but they aint now. Also, it makes sense to me to drill the oilway afterwards. (no chance of misalignment, radial or lateral).
 

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Dont forget before you start drilling the oilway, put a piece of metal inside the bush because if you don't, as sure as hell, when you break through you will hit the bottom of the bush with the drill bit.
 
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