Crank grind and bearing size

[Bluegrass40]

I am rebuilding my 2F. The crank journals have some damage. The machine shop recommended to gave them ground. Quoted it at $325 for machine work. They said that the cost was high because each journal is a different diameter. I was a bit surprised by that but found some documentation on line that supported it.

Any idea why this was done? Does that mean that each journal has a unique bearing? I have not found anything that suggest that you have to pay attention to which bearing goes to with journal......

Am I missing something?

 

[Bluegrass40]

Just found a crankshaft kit (crank and bearings) from clegg machine for $220

Crankshaft Kit 76-87 TOYOTA 4230/4.2L I6 2F" W/THREADED SNOUT-BOTH HAVE 2 KEYWAYS - W/ BOTH ARE ON THE SAME SIDE OF THE SNOUT

Has anyone ever purchased one of these from them?

 

[LAMBCRUSHER]

Your machinist is correct, to a degree of borderline insanity, but technically correct nevertheless... he might know a thing or two or maybe he is just trying to get as much as he can. Or both. Can you do a blanket grind, sure, but you do get what you pay for. Getting the rotating assembly balanced might be more important than blueprinting the crank... IMO... if I had the cash, I’d spend it on the blueprinting and balancing..,

 

[Bluegrass40]

@LAMBCRUSHER

Thanks for the response. I am not quite following though. I’m new to all of this... just trying to make sense of it.

The main journal diameters are speced at 2.636/2.695/2.754/2.813 with a run clearance spec of .0008-.0017. So it would seem that you would have to either grind all the journals to the same size (is that a blanket grind?) and get 4 bearings to provide the right run clearance, or grind them all by the same amount (.02) and get a bearing set that is for .02 undersized journals... and in that case it would seem that each bearing would be a different geometry (diameter or thickness).

I’m guessing that stock bearings are all the same thickness with different diameter to account for the different journal diameters. And I’m assuming that each bearing cap (and corresponding block geometry) has a different radius..... Is that correct?

Any thoughts from:
@cruiserdan
@Weber Sarge
@FJ40Jim
@Vae Victus

Thx for the education everyone!

 

[Bluegrass40]

Update.. I just found the FSM and it does note that the bearings themselves are different sizes for each journal. Makes more sense now.

 

[FJ40Jim]

It is common for engine blocks to have main bearing bores that get larger from front to rear.
This is done for 2 reasons: First, because it is cheaper to manufacture. A line boring tool can be setup with cutters for all the bearing bores so it can be shoved in the ass-end of the block to cut all the main bores to size simultaneously.
Second, the load in the crank & bearings increases from front to rear, with max load occurring right in front of the flywheel, hence the giant main bearing at the back of the crank.
HTH

 

[Bluegrass40]

@FJ40Jim
Thx for sharing you knowledge. Appreciated.

 

[Bluegrass40]

@FJ40Jim (Andy all you other experienced guys)

This is the first time I’m a getting into a motor or rebuild. I’m trying to learn everything I can and do most of the work myself.

This is going to stray a bit from the title of this thread... but I had a few more question that I thought of.

When I pulled the motor apart, I used some snap gauges and calipers to measure the cylinders and pistons. (I have some experience with precision measurements but have done little on note measurements).

I was pleasantly surprised because the cylinders we measuring quite round and very little taper and toward the tight end of spec. I measured in 6 spots (3 thrust and three axial measurements). I didn’t write my measurements down bc I was just doing it for my own experience and was going to rely on the engine shop. I then took the motor into a recommended machine shop for cleaning, magniflux and inspection. The shop said that the notes were out of round and tapered by .001-.002”. Possible that I measured wrong..... I asked the builder for his measurements and he just said it was .001-.002 out... he did not give me the individual measurements. (I didn’t really like that but I’m new to this... that may be normal). Before deciding what kind of $ to put into this I am considering pulling the motor from the shop and doing more inspection on my own prior to machining etc.

I want to make sure I understand the specs... the fsm shows wear limits and standard bore dims.


1. It does not mention taper or out of round... what limits should be used for that?

2. WRT wear limit of .008” (seems like a very large limit), does that mean that as long as all of 6 measurements from each cylinder are less than the upper bore diameter limit + .008, that cylinder is good? I’m guessing it is more complex than that.

It also instructs to measure/calculate piston clearance. The fsm seems to imply that you subtract piston diameter from the axial diameter of the cylinder.

3. Is that the only measurement position (on the cylinder) that is considered for piston to cylinder clearance?


Also found this other resource http://vintage.mitchell1.com/PClubData/chassis/enis76/V2I765295.pdf that calls out the same cylinder ware limit but also calls out taper and dif between cylinders. (It may be in the fsm as well and I just missed it). Are those limits accurate?

Maybe I’m overthinking all of this.....

Thx so much. I have really enjoyed learning about motors!

 

[FJ40Jim]

The .008" bore wear limit is a decimal error.