One Spun Big End Bearing
 

Fellow Pelicans

I spun the #3 big end rod bearing and I hope machining down to 1st or 2nd oversize will clean it up. Question - is it recommended to machine the other 5 big end bearings down to the same oversize or can I leave them at standard dimensions thereby leaving more material for future machining?

TIA
Bill
90C2

What engine?

1990 C2 3.6l

I would have the damaged journal welded,nitrided, and ground back to standard.

Totally agree,...:)

The only other option I would consider is to source a good used crank.

Regardless of which option you choose, the plugs in the crank should be removed and it should be thoroughly scrubbed out. Same goes for the rest of the engine and the ENTIRE oiling system. The oil cooler needs to be ultrasonically, cleaned, too.

Lastly, use dealer-sourced rod bearings. The aftermarket Glyco ones are nowhere as good.

Adding a little more to Steve's excellent reply is finding the possible oiling issue that may still be there( if the failure was not a rod bolt) . A number 3 rod bearing is not the first rod I would suspect to have any oiling issues. Blockage of oil passages or wear/damage of the oil pump should be considered. #3 rod is too close to a good source of oil to have problems.

Gentlemen

I'm surprised that you don't consider machining to 1st or 2nd oversize an option!

Confused
Bill
90C2

Price the bearings and check availability. Bearing selection/pricing can be pretty dicey these days. I personally would not do it if I had the choice. Play it safe and stay standard/standard.

Aaron

I'll at least have to replace all the big end bearings - they all have a few scratches. I can't see any scratches on the crank journals - so I'll at least need to have them polished. Am I right, but is a set of big end bearings gonna cost me around $1200.00?!


TIA
Bill
90C2

Standard main bearing set is $251.25 for the set.
Standard rod set is $185.50
This is for the Glyco brand.

If you go 1 under on the mains/rods, expect $1200.00 each set!
Right now the .5 under rod bearings are priced OK, but it does not mean they will be in the future. Right now, the only bearings Glyco is supporting are standard dimensions.


You need to measure all rod journals to verify if all they will need is a polish. Sometimes the journal will look ok, but will no longer be round.

Interesting pricing - Do I have this straight - if I go +0.25mm on the big end rod bearings I'll expect to pay around $1200.00 but if I go +0.50mm it's $146.00 and $185.50 for the standard set. The main bearing set are priced similary only the price of the 0.25mm and 0.5mm are the same at around $1200.00 and the standard set is $251.00. If so, now I understand the reason to stay standard and weld the journal that had the spun bearing.

As far as oiling goes, if I understand it correctly, the oil enters the crank at the nose bearing at the #1 cylinder end - the number 3 bearing is the last rod journal down the line to receive oil other than the rear main bearing (i.e. the main bearings all look good) so the blockage must have been right at the journal.

All comment welcome

TIA
Bill
90C2

Oiling is at both ends. The Rods that usually see a problem are #s 4 and 5. So it would be #6 first then 3 to get oil.

You got it, Thats the reason you stay away from undersized bearings.

Aaron


Other than what was mentioned above,
Is there any reason that one journal can't go undersize and the the other 5 remain standard. Is there any issues with balance with one journal having a lower dynamic weight. The fact that the bearings are sold individually makes one think the reason for this is one journal can be machined.

If I stay with "dealer sourced" bearings as Steve recommends do I have the same oversize options and are the bearings marked "Genuine Porsche" or "OEM supplier" by our host considered the same as a "dealer sourced" bearings?

TIA
Bill
90C2

Repair one journal to standard. If more that one [journal] needs repair, source a new or good used crank.
I don't know the logic behind selling bearings as individual pairs, but IMHO, I feel certain it's not so you can size rod journals separately.

According to an importer that sources bearing directly from Glyco, the bearing specs are the same. For example, GT3RSR bearings from the dealer and bearings directly from Glyco are identical according to the manufacturer. There is a 100% + price difference. That said, we still use the RSR bearings for a many engines as possible.

Gentlemen

It has been suggested to me to have the journal chromed and machined to size rather than welded and nitrided as it has been the machinists expereince that welded cranks are prone to breaking aftwards.

Any opinions

Thank you
Bill

I've had bad and good results from both methods. As with most processes, the quality of the craftsman is paramount.

I generally go with welding because the craftsmanship of the guys at Marine crank is exceptional.

Henry,
Can you give an address or tele for marine crank? Thanks. Paul.

David @ Marine Crank
2155 S. Grand Avenue, Santa Ana, CA 92705
714.549.2388
Fax 714.549.1382
Email: CACranks@yahoo.com

http://www.marinecrankshaftinc.com/

I believe that using one undersized / oversized would mechanically be fine. But for the reasons cited above, it's not generally done. Typically, it's easier to find a good std/std crank and/or have it rewelded by a competent shop.

-Wayne