Gudgeon pin width (reaming out for floating pins again!)
Turbo Mini Forums

Hi lads

righto, I did write this down last time i was down the garage, but have since misplaced it!!

Does anyone know the width of the std gudgeon pin?

And when reaming out, what clearance should be given? would it be reamed to give the same clearance as the piston? (i guess not as different materials??)

From memory (i think Sprock posted a thread a while back, but cant seem to find it now), for fully floating std size pins, the little ends needs opening up to 13/16" (same diameter as a cam follower?

and the verdict was that a bush is not necessarily needed?

having not reamed cast iron before, would this adjustable jobbie be man enough?:

http://cgi.ebay.co.uk/HBM-ADJUSTABLE-HAND-...%3A1%7C294%3A50

or should I look out for a set 13/16" reamer?

hoping to get the short motor built up over the next week, just waiting on the arrival of a hardened/balanced crank, and obviously getting these little ends sorted.

Cheers all

Joe

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

righto, found my notebook, my pins measure 623 thou (or 5/8" ish) diameter, so might have imagined the post about 13/16"?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

yarp, i didnt realise 998 and 1275 pins were different diameters?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

i reamed mine until they just fitted the rod.

I know it sounds naive Joe, but how did you make sure they were reamed dead parallel with the big end ?.

nope,

I am a god damn cowboy.

lol, spend about 2 hours searching, the only one i can find

http://www.engineering-supplies.com/show.asp?id=5246

....and theyre out of stock...brilliant.

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

can you not put some grinding paste on your penis and use that?

wouldnt touch the sides nic...

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

wouldnt touch the sides nic...

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

lmao @ nic

Mine did a particularly good job on the valve guides

Gonna attack them this weeknd

any advice on doing this, ive never reamed anything before

is a bit of oil good, or cutting fluid better?

do i got i full on, or enlarge it bit by bit?

Cheers

Joe

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

fit the reamer into the bore , expand until its nipped then start opening out very gradually,

your only going to take 0.002" at most, so only move the nuts on the ends of the reamer 1/6 flat at a time,

make sure the reamer passes fully through as these things tend to crown a bit,

carl

Edited by fastcarl on 4th Aug, 2009.

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

excellent, cheers carl

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Please let us know how you get on as I am at this stage with my third engine build (for the same car) this year. I am tempted to broach the little end eyes rather than ream them, as there is a better chance of keeping the bore square to the rod.Also, I know to my cost how easy it is to ream just a little more than you intended.It sounds as if you intend to run the gudgeon pins direct in the rod, as I do. This will leave the option of bushes later, if necessary.I am also tempted to drill a small hole in the top of the eye to allow some oil to reach the pin, inside the rod eye. What do others think of this ?.

yeah, bushing is a back up plan if i cock this up

so you mean drilling a hole in the top of the little end? to collect oil?

paul s pointed out that all the small bore rods have oil squirters coming off the big end, so there should be loads of oil spolshing about up there?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

i think i drilled a hole on mine.

I keep forgetting that you are doing a 998 and I only ever think about 1275,s - sorrry.

Yes, I realise that there is usually a fair bit of oil getting up inside the piston, but I thought that it might be a bit tricky for it to find its way into the con rod eye, without a bit of help.I know tyhat on some engines with bushed little ends they do have a hole in the top for this reason.Does any one think that a hole, say,3mm in diameter,is likely to affect the strength to any extent that matters ?.

Done a bit of careful research and measuring now on this subject.

The interference fit on the 1275 Midget rods is 4 tenths and, although the pin is initially difficult to press out due to "stiction" it is very easy to press back using just the vice.

Interestingly, all the pins that I measured were 1 thou oval,just at the ends, due to the piston oscillating on them.Does not seem to be a problem.

As it is so easy to press them back on I am now going to stick with standard set up, but, in answer to a question earlier,I reckon a 1 thou clearance is plenty so, adding on the interference fit, only 1 1/2 thou would need to come out of the con rod eye (as already suggested 2 thou max)
If you take out less then the worst case scenario is that you end up with an easy press fit and teflon buttons for safety - over cook it and you are in for a lot more work

Have reamed my rods out (1275) however one of them has a slight bit of rock to the gudgeon pin, no up/down movement just if you hold it by both ends you can wiggle it slightly.

Is this a problem? Is it better to source another rod?

Sounds as if you have belled the ends of the rod slightly.Probably not too much of an issue on a standard engine but if you are going to turbo it maybe you should bush the rod and start again.

Aye k headed turbo. I'll get another rod i think.

would honing be a better bet?