ReinerFink

I am getting my ducks in a row for a top-end rebuild on my 993. As part of this, I will be replacing rod bearings. The "shiny" ones from SmartRacing are what I would like to use, however they come in 3 sizes depending on your rod and crank diameters. Since I wasn't planning on cracking open the case I was wondering if there is any hope of measuring the crank diameter acurately enough? Thanks,

-reiner

Mike J

I am not sure if you can get down the spigots and measure accurately the crank, but you can assume standard size, and then use plastigauge to check the clearances. Don't forget to replace the rod bolts with ARP bolts, that cures a weak part of the 993 engine.

How many miles on the engine, and why do you think you need to replace the rod bearings? Usually, the rings, and valve guides/valves are good enough.

Cheers,

Mike

ReinerFink

Thanks Mike, I have read your writeup and it has given me much confidence!

The car has 120k miles, and I am dropping the engine to replace the brake line (hard line) that runs to the RR of the car. I decided "what the heck" and I am going to do a rebuild while the engine is out. I have a lift in my garage, and I have all of the factory tools for engine removal and setting timing etc etc.

Check on the ARP bolts (p/n 204-6005, right??).

I track the car alot and I want to just make it last for another 100k+ miles without having to see the engine come back out.

The heads are going down to Steve Weiner for bigger valves, aasco springs and the full meal deal there. I have been tracking down bits and bobs (found Threebond 1194 at the Seattle Ducati dealership) and I was thinking about using the "HX" standard thickness bearings.

The smartracing pdf mentions "We do not recommend using plasticgauge because the rod bearings should be 'crushed' only once."

-reiner

Steve Weiner-Rennsport Systems

Thats VERY good advice; we only use micrometers for measuring crank journals.

Standard bearings should be just fine unless the crank is undersize or has been machined.

Geoffrey

As mentioned, the Smart Racing bearings should not be crushed more than once, and plastigauge is not accurate enough to determine the clearances, you need to use a bore gauge on the rod and a micrometer on the crankshaft to determine the bearing shell thickness. The Smart Racing bearings come in intermediate sizes which means that you are altering the clearances by only tenths of a thousandth (.0001), not by standard vs undercut size (approximately .010). You need to split the case to properly measure the crankshaft. Here is an example from my last engine build of the kinds of measurements you want to record.

Also, if you are tracking your 993, the factory rod side clearance of .005 is insufficient and I recommend increasing it.

Mike J

I think the idea that bearings should be crushed once is an opinion, since I have also talked to other other engine rebuilders who have exactly the opposite opinion. My suggestion of using plastigauge came from the fact that the case is not split...how else would you do it with that restriction?

Cheers,

Mike

ReinerFink

Geoffrey, I assume if I were to split the case I could measure the rod side clearance before dissassembly and have a machine shop take a bit off of the sides of the rods at the crank end to give me something a bit above .005? And roughly how much is a "a bit" ?

-reiner

Geoffrey

It will depend on the bearings. The Smart Racing bearings are a crush once bearing.

I'd run between .008" and .010" rod side clearance on a racing engine.