Reaming rods for floating pins
Turbo Mini Forums

I want to convert my S rods to run floating pins. Can anyone advise a good place to get this work done and what sort of price to pay?

Cheers
Matt

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1/4mile in 13.2sec @ 111 terminal on 15psi

I seem to remember a topic on this before, I think Mr Austin offered his services.

Yeah ive seen a couple of posts on it but don't recall any companies mentioned? Hmm, I'll have another look.

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1/4mile in 13.2sec @ 111 terminal on 15psi

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=133878

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=11166

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=9010

ah yep i'm making up false memorys again...

Just had a look at my rods and they might be reamed already. :)

As far as I know the floating pins need a bore of 13/16 in the rods. From another post about cam followers it was determined that the size of these were 13/16. I tried one of the followers in the rod (I don't have any floating pins to hand) and it could be pushed in by hand without much force.

1: What is the size of the standard rod little end?
2: What kind of fit do the pins need to be e.g easy to turn in rod or a good fit that takes quite a bit of effort to turn?

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1/4mile in 13.2sec @ 111 terminal on 15psi

the pin i have here comes out at 811-812 thou, but thats using verniers.

Do you have a measurement for a standard gudgeon pin? The only pins I have are still fitted to pistons.

Im trying to get an idea of bore difference, if its a significant amount I can be certain that my rods have already been reamed.

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1/4mile in 13.2sec @ 111 terminal on 15psi

the 811-812 was for a std one from an S rod.

Im completely confused now!! As far as ive read rods need to be reamed to fit floating pins. Ive had a look on MED's website and it doesn't mention anything about reaming, if anything they mention supplying a bush to reduce the size of the little end to 18mm to suit the gudgeon pin??

Ive been offered a set of omega forged pistons that are fully floating, but I still can't work out if reaming is nessesary to fit them?

Ive also read somewhere the A rods used floating pins from standard, as mine are S surely this would mean that they don't need reaming?

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1/4mile in 13.2sec @ 111 terminal on 15psi

How are the gudgeon pins fitted to the pistons on the cooper s rods?

Edited by Jordan on 8th Sep, 2007.

Back once again like a renegade master

Ahh,

ok,

ther are pistons available with smaller (18mm) pins, with these you press a bush into the rod so they don't need machining tobe floating,

If your omegas are fully floating they may well be of the 18mm pin variety,

only small bores had floating rods, which became nonfloating at A+ IIRC.

so you will either need to ream the S rods to clear a std pin (about 2 thou i think) or get them bushed and reamed to the 18mm of the smaller pins if thats what they are.

so reaming either way...

I measured the bore in the rods and it was 20.64mm to 20.68mm between all four rods. Only had a vernier, so not the most accurate measuring equipment.

I tried a cam follower in the hole as this is a known 13/16 in size (which Ive been told is the ream size for floating pins) and it could be fitted into the rod and turned quite easily. Ive never fitted any piston to rods but as far as I know the pin has to be pressed into the rod which makes me think they have already been reamed?

Edited by matty on 8th Sep, 2007.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Sounds like it but this might just make sure that it goes in with no seizures (like on vlave guides).

Isnt there caps on either side of th piston for floating pins?

Edited by Jordan on 8th Sep, 2007.

Back once again like a renegade master

Gudgeon pins are all the same diameter for the 1275. Hone the rod little end for a clearance on the pin, thats all thats needed

There are some forged pistons using smaller diameter pins so the little end needs bushing for them to fit the rods

A piston described as floating pin usualy means that there are circlip grooves and an ever so slightly shorter pin to stop the pin moving about.


Hone the lttle end, and get some PTFE buttons made up that press fit in the pin ends to prevent scuffing of the bores

Its not a common modification, so chances are the rods you have are standard. Check the little end sizes in the workshop manual

Do you not yet have your pistons?? I would leave the little ends alone untill you have the pistons and pins, that way your machinist will now exactly wht size to hone the little ends to

Edited by Sprocket on 8th Sep, 2007.