When I was younger, I worked for a gentleman who had a auto parts and repair business. One day I asked him about tolerances. I was rebuilding an engine for myself. He laughs and says," Well, if you build one with =/- 0.010 tolerance and go with the lower values, and one with the higher values, one engine will be about 6" longer than the other!" Than he told how to set it up right. I ended up with a very good rebuild.
Les
In all the years that I built and repaired engines it never occurred to me to mic bearing inserts so I am wondering just how precise all the bearing that I installed have been. And I am borderline obsessive in being meticulous. I won’t bore everyone with all the details but I always plasti-gauged bearing clearance and often dressed down bearing caps to bring the clearance down to midway of the specified range.
Wait.
You’re saying the bearings are consistent but wrong? Doesn’t that point to better tolerances over time - it’s just that these bearings aren’t built to the right target value?
It’s not displaced decimals. The .010 is ten thousandths of an inch and most cranks are cut .010 or .020. Anything over that is iffy and usually means a discarded crankshaft.
There are .001 oversized bearings available for polished, non-cut crank journals.
The crank end play spec is .008 to .016 and yes, I inadvertently added a non-needed zero on the 16 and the 15 part.
In a nutshell, the crank end play is 8 to 16 thousandths so the .0016 and .0015 is a faux pas.
On another note, I decided to take a look at the rod bearings and the differences on shell thickness is almost unnoticeable at under .0005 an inch so no problem there.
Just to update this for those interested. After receiving another set of main bearings (these were Clevites) a careful inspection of the thrust bearing showed that what I feel to be the 3 existing flaws in the Sealed Power thrust bearings do not exist with the Clevites.
Shell thickness, overall thrust bearing width, and parallelism of the thrust surfaces mike out to under a 1/2 thousandth of an inch and that bit of minutae could be nothing more than the feel of the fingers on the micrometers.
To be honest, this still has me totally baffled due to 4 sets of the SP bearings being the oddities and the claim by Federal Mogul support people that those bearings match the engineering blueprints.
How in the world one can take 2 halves of the same bearing with a radius difference of .0015, mate them together, and come up with an acceptable oil clearance is beyond me and consider a concaved thrust surface to be acceptable is beyond my comprehension.
This could lead to excessively tight oil clearance on one side of the journal and excessively loose clearance on the opposing side.
Note that there was no problem with the regular 4 main bearings on the original 4 sets of bearings; just the thrust bearing halves.
Based on those oddities, I just flat could not bring myself to slap that thing together like that.
Anyhow, for those putting an engine together, having a set of mains installed to cure an oil pressure problem, crank kit, and so on it might be a good idea to look those bearings over or have them checked very closely.
Thanks for the info. In our world of making time and constantly trying to deliver cars when promised I doubt many people would bother to mic a new set of brand-name shells. I’ll be a little more vigilant in the future myself.
Miking a set of main bearings was something that I’ve felt a need to do in the past. The only reason it happened this time was because of noticing the texture of one thrust bearing compared to another. It was only a bit later that the thought of different thicknesses crossed my mind and I put the mike to them.
Any picture pulled up from parts sites showed those thrust bearings to be made like that with different textures and it appeared to be the norm.
At this point, I’m still a bit bugged about it because I hate to remain in the dark as to why. The email and phone call to the manufacturer certainly didn’t clear things up for me.
I might also add that in reference to the concaved thrust surfaces I was told (not a direct quote) “that the bearings will straighten themselves out when tightened down in the block”.
Not buying that for a second either… 