Mark Brook

My 1990 C2 had a slight tapping from the engine internals which after strip-down proved to be the dreaded number 6 bearing @ 108,000 miles!

The shop have just received the crank back from being reground, so it will require 0.25mm oversized bearings, a set of main bearings, top and bottom gasket sets, twelve new con rod nuts and bolts, intermediate shaft bearings, a set of rings plus a second hand con rod.

My local OPC have told me that they do sell single con rods, as long as I know the weight of the ones already installed because they range from 624g to 696g.

I intend to source as many parts as possible from Euro Car Parts, but wanted to ask the people that have already had this work done, what if any, were the benefits in using ARP nuts and bolts instead of standard items?

Has anyone fitted a second hand con rod and if so did this alter the
balance of the engine in any noticeable way? Do pistons and con rods have to be balanced together?

The top end was rebuilt roughly 10k ago and has been removed 'as a piece' so it's only the bottom end being worked on, and I haven't gone for any upgrades in the power department. All I want is a reliable, leak free engine capable of fast road and the occasional track day.

Your input would be much appreciated.

Cheers,

Mark '90 C2.

altarchsa

Yes, I've replaced two rods in several rebuilds on my engine.

I just weighed the replacement rods to confirm they were within the weight differential limits and matched them at horizontally opposed cylinders, heaviest toward transmission I think is the recommendation, and it ran smoothly. However, this last time around I paid the machine shop a nominal fee to balance everything, rods, wrist pins and poisons, both individually and as sets. I know Porsche's tolerances are tight, but they still use a range of tolerances to match parts. If you have them balanced, they will be exactly the same.

You wouldn't believe the difference I found! The engine is so smooth, you can place your fingertips on top of the fan housing and not feel ANY vibration through the entire range of revs. The difference was truly amazing.

I would very strongly recommend you have your machine shop balance everything, as groups (pistons, rods, pins) and as sets (cyl. #1, #2, etc.) especially considering the problem you had. They can "cone" the inside of the ends of the pins, and they just nibble the unnecessary material off the edges of the pistons and rods. You might want to review in advance with them the areas where they will be removing material are not structural. These guys are usually pretty smart, but they may put some kid who doesn't know anything on it, and you don't want to come away with compromised parts.

I would also confirm that they re-balanced the crank with the re-grind. Depending on the standards of the shop, they may not have.

altarchsa

"pistons", not "poisons". Sometimes I hate autocorrect.

I forgot to mention that there are weight stampings/dirge marks on the rods and pistons, and you should start with a replacement part that matches the numbers and symbols on your existing parts.

altarchsa

dammit,"forge", not "dirge"

jimq

hit the little paper symbol at the bottom right of your post and you can edit after you post.

altarchsa

Oh, cool. Thanks.

race911

Should be able to pick up a full set of used ones cheap. Enough are replaced with Carillos, etc. I personally don't have any 964 sets around now (at least not inside engines). I think the last set I saw for sale was around $100.

One thing I was always nit-picky about, based on experts much, much, much more capable than me, was grinding cranks. But the engines I was doing when I had my shops were in the 2.4/2.7/3.0 era. Getting them re-nitrided was tough back in the '80s-'90s. Maybe it's a no-brainer now.

doruiacovescu

the noise from your engine clacking was similar to this?

ALEX P

Hi Mark,

I think the stock rod bolts are use once items whereas the ARP can be tightened numerous times (not that you want to!).

I also think the ARP bolts are a no brainer while you're in there just and well worth the investment if only to give you the extra confidence.

crg53

If you are looking for a used set, check out THIS SITE No affiliation.................. He has always got a good selection of used engine parts.

Mark Brook

Thanks for your input gentlemen.

Altarchsa, I shall definitely ask my independent to get everything balanced at the machine shop before instalation seeing as it made so much difference.

Ken, My shop only told me that they had the crank reground and that I d need +.25 bearings.........they never mentioned re nitriding. Would a machine shop do that as standard after a regrind?

Alex, I ve been following your rebuild and like you say, the bottom end isn't something I ever want to have done again! The ARP product does certainly appear to be in a diffent league to standard, so I shall place my order today.

Steen, thanks for the link, the guy even has one on his site for $30 but as yet I m not sure of the rod I need. I ll check with the garage today and hopefully save myself a few £ buying secondhand.

Doruia, I listened to your noise and have to say that is similar to the sound mine was making. I started by replacing the fan bearing, then had the alternator rebuilt including a new bearing, then I had the valves re adjusted, oh, and lastly a new chain tensioner....... All to no effect. I hope yours isnt the same as mine though...........

Cheers,

Mark.

Mark Brook

Alex,

Whare did you buy your ARP nuts and bolts from?

Cheers,

Mark.

sundog

What caused the bearing to go? Check the oil return tubes over the passenger rear tire to make sure that there isn't a slit in it that can let sand into the oil. Ask me how I know.

J richard

Was the rod overheated and burnt? or bent? Otherwise I don't know why they aren't resizing the big ends and rebalancing.

A crank can be polished without retreating but if it's ground It HAS to be renitrated.

ALEX P

Hi Mark, I bought mine from Arrow Precision here in the UK, think they cost around £220 and weren't a lot cheaper stateside.

If you are going to buy from the USA then Don Weaver at EBS Racing is a good guy to deal with, very helpful and knowledgeable.