Rod bearing size
 

Hello, im rebuilding my 1989 turbo supra, its torn down to nothing but the block and the crank because im not replacing the mail bearings or turning the crank because there was no damage to any of the bottom end i just had to replace the pistons due to a dropped valve.

My question is since im using the factory rods, and factory crank how do i tell what size bearings to use?

I talked to a mechanic friend of mine who worked for toyota when the MK3 supras came out and he said it has something to do with the six numbers stamped on the block and the numbers stamped on each rod but its been fifteen years since he worked there and he cant remember what the formula is or what numbers need to be added together to find out bearing size.

Any one have any idea how to get this info?

Your local parts house should be able to tell you. It should come up on the list if they need any special block numbers. Ask for the standard bearings, then measure with a micrometer or caliper to see if any of them are sized down as if they have been turned during a previous tear down. I would never assume the engine has not been worked on before, considering the critical-ness of the bearing clearances for a healthy engine.

The numbers are stamped into the block where the oil pan flange bolts up... toward the back on the driver's side. There's no code, those are the bearing sizes as they were installed at the factory. If you follow the procedure in the TSRM you can get MUCH better clearances then by just using the same size that fit the crank 20+ years ago...

It's kind of foolish to not replace all the bearings while you're in there, IMO. Damage or not the bearings and crank both wear and continually lose material... you're already doing well over half the work.

Did you do a leak down test to see how the rings are holding up?

Shame on your "mechanic buddy" for not giving you crap for trying to take the lazy route. :P

well im on a strick budget and really dont want to put alot into this thing cuz i might just sell it any way. but its still in the air, another thing is my block mating surface.

there was about a quarter inch chip only going very very shallow into the block, almost like someone tightened up the head bolt with a peice of debris in the threads and it just popped a very thin layer of metal off, its not affecting any of the commpression seals but its very close to a water jacket seal, but not on it just close.

I cant afford anothe block so i set up some JB weld to fill in the low spot and sanded it down to the surface of block.

Now i know thats not the best way to fix it but since its just around the rear intake side head blot and not affecting any crucial mating surfaces, that should be ok right?

SO that being said i cant have the block decked cuz the bad spot looks a little to deep to take off enough metal to compinsate, and with the JB weld on it it obviously cant be decked, im wanting to use a metal head gasket so i need a very smooth finish on block.

If i used like 800 grit, then 1200 grit, then about 1400 grit wet sand on a flat sanding block could i get the finish on th block im looking for?

The head has already been decked and looks like glass.

NO... or, I'll put it another way... NO.

JB Weld is not made (specifically) for repairing block decks... if it needs to be filled (which it sounds like it does) you need to use the right materials, especially if it's that close to a coolant passage. The name of the stuff I've seen used escapes me now... If I think on it I'll post back. You should be able to find it via Google; It's made specifically for repairing blocks and heads and is made to handle the constant heat cycling and the expansion and contraction that comes with it.

A MHG? Forget it... I hope you give any buyer a disclaimer and list of all the corners you've cut and skimped on... they're liable to sue you in a month otherwise.


EDIT: Belzona Super Metal (No. 1111) is the favorite that I know of. It's not cheap though, but there do appear to be other products which are less expensive and still preferred over JB Weld. If you're close to the coolant passage at all (especially if the jacket on the HG is likely to overlap the repaired portion) I would definitely not use JB. A lot of people have had good luck with it, but plenty have had issues too and there are better products available.

EDIT2: I just found my old notes on this. Cat used to sell Belzona, I'm not sure if the still do. I bought a small quantity a long time ago from a local industrial supply shop but it wasn't for engine repairs. A friend of mine (another Supra owner) said he really liked Devcon... adheres better than JB Weld but is a lot less expensive than Belzona. I don't have it written down but I think you would want the Devcon Plastic Steel 10110 putty, it's steel filled unlike their Home Depot JB Weld equivalent.

ok thanks for the info, im really not trying to cut corners i just dont have the money to have the crank turned and also but main bearings.

from the looks of the rod bearing lobs on the crank the crank seems to be in great shape so thats why im not to worries about the main bearings.

as far as the block goes i already put the JB weld in it unfortunatly but i am going to see if maybe i can heat it up and knock it back out but who knows i may be stuck now.

I was referring more to the MHG on an uncut block and the JB Weld.... The MHG is an absolute NO in most people's book; The JB Weld is more suited to fixing handrails... but plenty of people swear it works so just cross your fingers.

wow, jb weld on the block deck...scary! decking a block at a reputable machine shop should only be about 35 bux. ill have to check my reciept.

and turning cranks, about the same, at least polishing. which would be what theyd do, then you still use standard bearings, and u have a new surface to break in on.

do it right, or dont do it at all. theres not really a way to save money when doing an engine. if you assemble it all yourself and are careful, then you can prolly have all the machining done for under 400 (i did, and i spent 360 for machining, then 110 on pistons, rings , rod and main bearings, and 150 on gasket kit). im also buying a MHG, but thats me. so for about 500 bux, you can rebuild a motor with all new bearings and rings, if you dont bore/hone, figure 650 if you do.

A lot of people and even shops use JB on block decks... the good ones are VERY picky about where they'll use it though. I'd still like to see pictures of the block in question.