Honing 1275 little ends for full floating pins
Turbo Mini Forums

Are there any reasons not to do this other than increased wear rates. The wear rate is not a problem as it will be stripped after fairly short mileage anyway.

Any other reasons not to? Obviously teflon buttons in the pins are required.

I believe Will and Ben H run full floating pins but i think they are on bushes.

your biggest problem is keeping any machining parallel to the big end, this is a serious concideration when bushing, but might be abit easier when its just a hone out.

I've seen the future and tbh its Pie

Im interested in buying teflon buttons for 1275 engines if anyone makes them. Just btw :)

Apart from this, I see no reason why not to do it. My 1417cc engine has got these:

http://home.online.no/~lyngset/minebilder....Type=&pExPic=0;

I've done this to my engine, I can't see any problems.

Team Racing

When you say converted to fully floating are you fitting bushes or just honing out the rods a little?

I'm not sure I like the idea of the pin rotaining in the rod without a bush in there but if people are using it and it's ok then I'd really like to hear about it, especially if there are pictures too.

Every day is a school day ...........

How fast and how expensive ...... the same question...

Why isn't this a good idea in your book? My rods are without a bush.

my rods are also without a bush, (but have teflon caps)

The way I see it, if anything is going to wear it's going to be the piston, yes the rods will wear in time, but how long?? my engine will not see anything like the milleage of a daily driver.

Team Racing

I think it will not be a problem pin to rod (without a bush) as the pin is NOT rotating, At worst it's only moving through an arc of a few degrees and should be fine.
Regards
Dave

danboy, the laws of real world physics say that it's won't just move in an arc.

Think about a spring rotating as it's compressed ... at the higher load point the friction between spring and seat will be higher than the low load point hence the spring will not recover to it's original position but slightly rotated.
After several cycles it will have rotated a full 360 degrees and be on it's second lap. The relative wear rate of sping and seat are dependant on many things but it's likely that both will wear eventually.

With this in mind think about the forces, both loads and rotational on the pin and come to your own conclusions.

The wear rates for each part will be dependant on several things, surface condition, material, type and timing of loading etc. etc.

Rod material won't make great bearing material I'm sure. If the pin wears before the rod then fine, cheap and easy to replace. If the rod wears first then you are into an expensive replacement (especially if it's modified) plus the cost of balancing the assembly agian etc.

The point about milage is a good one, if it doesn't do many miles between rebuilds then you can at least measure and find a problem before an expensive disaster happens.

Every day is a school day ...........

How fast and how expensive ...... the same question...

mine are fully floating and dont have bushes. i took it apart after 10,000 miles and fitted new pistons without holes in the top and the pin felt fine.

RogerM The laws of real world common sense says that it can only move in a small arc each revolution.
Applying your spring analogy, there is some small amount of friction that could "inch" the rod a little futher round on each engine revolution but this can only be a good thing as it will spread the pin wear evenly round the ring rather than concentrate the wear in two places as it would in a press fit pin. The absolute minimum number of revs this would take would be of the order of 20 engine revs / pin rev.
Now if you think about what is actually happening at the rod/pin interface and apply your logic the pin should not rotate at all as the rod moves in a forward and backward direction for each cycle and any small amount of friction in the joint should cancel each other out and return the pin to its starting position.
In reality I would imagine the pin will rotate (relative to the rod) at such a slow rate that the apparently incompatable materials are more than adequate for the job.
I think you missed one key thing off the list of wear rate criteria and that is the relative speed between the two faces and this will be so low that it should not present any problems in this case
Regards
Dave

end of the day if it does wear then fit a bush later

sorted

I was a little unsure at first, nobody seems to mention this mod.

Thanks for the replies guys :thumsup:

danboy you are forgetting the very different loads on the pin at top and bottom of stroke let alone the transients throught the stroke.

Trust me, I see this sort of thing day in and day out ......

For a low milage motor your probably ok as it'll be inspected regularly. If it's a daily then I'd be unhappy to have that mod in my motor.

It is however a great mod if your playing with pistons as it makes changing them very easy!

Every day is a school day ...........

How fast and how expensive ...... the same question...