13 replies to this topic

[micromontenegro]

So I my engine (998 A+ from 1993) is at the shop for boring, and press fitting the pistons to the con rods. I go to happily pick it up on friday, only to find the tech scratching his head and telling me I bought the wrong pistons, as the gudgeon pins are far too small for my rods. And they already bored out the block for the pistons!!!!!

 

I go home, sad and feeling dumb. I should have never bougth those Nural pistons on ebay. And I already gave a good rating to the seller. 

 

Doubt sets in. I break out the manual and the caliper. Lo and behold, the new, "wrong" pins are about 15.84 mm- the correct diameter. The old ones mike almost 17mm, as do the small ends on the rods.

 

Pray tell me, what went wrong here? Did someone mess with my connecting rods before, or are there different (so different) small end diamaters for the late 998s?

 

More importantly, what can be done? If I get new connecting rods, how can I be sure the will they be the correct diameter? Can the old ones be bushed, as the shop tech said? Please consider I live in Venezuela, so I buy spares sight unseen, and pay dearly in shipping costs.

 

Thanks for any and all responses! 

[Dusky]

Maybe you got press fit and floating pins mixed up?

[micromontenegro]

Nope, they are all press fit.

[Dusky]

Got a link to the ebay add? There is no difference between the press fit pins as far as I know

[David128]

Small End bushes used to be available from somerford but currently showing out of stock. Moss Motors part number 330-428 . I would check sizing first they could be machined if they are too big but not vice versa

[micromontenegro]

http://www.ebay.com/...=STRK:MEBIDX:IT

[gazza82]

Any part numbers in the castings of your con-rods?

[micromontenegro]

Any part numbers in the castings of your con-rods?

Give a few minutes and I'll post them.

 

Thanks a lot to all!

[micromontenegro]

My wife found these numbers: 12G.127 and 23875 Z22 15-1. According to this catalog: http://danamotorssac...atalog_2012.htm 12G.127 is supposed to have a pin diameter of .625, which is a far cry from the .669 mine are. 

 

Edited to add: and were supossed to have circlip pins. So somebody bored them out and pressed who knows what kind of bigger pins in.

 

Makes you want to burn the darn thing down.

 

And the previous owner.

Edited by micromontenegro, 05 October 2015 - 03:25 PM.

[matty...]

your only option is to rebush the rods,I would suggest phosphor bronze bushes. Easy enough for a machine shops to make, and press in and then bore and hone to size. If the circlip grooves have been removed in the Pistons then get some PTFE buttons made up and have it as a fully floating setup.

We had a massive engine failure last week at work on a customers car, where in a similar situation they decided to bush the Pistons...it did not end well! Lol

[ACDodd]

Just get another set of rods, problem solved.

Ac

[Dusky]

http://www.ebay.com/...=STRK:MEBIDX:IT

pistons for floating pins.

[micromontenegro]

Many thanks, folks. I am actively looking for new rods now.

[Spider]

My wife found these numbers: 12G.127 and 23875 Z22 15-1. According to this catalog: http://danamotorssac...atalog_2012.htm 12G.127 is supposed to have a pin diameter of .625, which is a far cry from the .669 mine are. 

 

 

The Rods - Press Fits and Floating Pin types - are the same forging and in fact machined the same.

 

In the 'earlier' Rods, as some of the other guys have hinted at, they fitted a bush for the floating types (that usually use a pair circlips in the Piston to retain the pin). You can buy the Bush;-

 

http://www.somerford...roducts_id=6625

 

but it will need to be honed (not reamed) to finished size and be square to the Big End.