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Allan G, gavin eisler
Total Likes: 4
Original Post (Thread Starter)
#844145 03/26/2021 1:27 PM
by drunkenmonkz
drunkenmonkz
Man, I hope to not have to bug you all every step of the way of this motor build...
So a65 crank ground to .010 under. New map rods with .010 under (over?) Bearings to match crank.
Dry assembly using plastigage on cap side and I'm getting .003 from it.
Now the plastigage was old, cold and kinda crumbly. That being said I warmed it a little over my space heater so it wouldn't disintegrate when I cut a piece long enough to use for measuring.
I believe tolerance is .0015..
Soooo....
Confused about what I should do at this point. Get new .020 bearings and have crank reground..? That sounds like, well, a pain in the ass and excessive.
Say sod it and clamp em together and run it. mind you I'm hoping to build this to be a NICE motor with all the performance upgrades available within my tax bracket.
I don't plan on racing it but I don't want to think twice about pinning the throttle for a minute or two.
Input is, again, greatly appreciated.
Thanks guys
Liked Replies
#844690 Mar 31st a 09:22 AM
by C.B.S
C.B.S
You state the crank is -.010 under

What do the journals actually measure after grinding?

Perhaps we should start there and move forward before ruling anything else out?

Not uncommon for a crank grinder to make a mistake, it's not right, but we are human and things like that do happen...
2 members like this
#844287 Mar 27th a 03:44 PM
by C.B.S
C.B.S
When you checked, was each rod bolt torqued to spec?

Sounds silly, but you would be surprised what the proper torque can do in terms of the proper clearance

You can also use a bore gauge to measure clearance
1 member likes this
by Stuart Kirk
Stuart Kirk
Ok, here's more info. I have my basket case '59 BSA A10 engine apart.

The crank is freshly reground with those Hepolite inserts in MAP rods.

The inserts were installed in the rods and the bolts tensioned to MAP's stretch specs before going off to the machine shop.

The machinist was instructed to measure out the rods and go by that dimension when grinding.
[Linked Image from i.postimg.cc]
So I went and measured the rod journals...

BSA's first regrind calls for 1.677" to 1.6765". These journals measure out at 1.678".

That is a thou to a thou and a half larger than recommended. This would make up for the Hepolite shells being thinner than they should be.
[Linked Image from i.postimg.cc]
This tells me that those Hepolite inserts are indeed sized incorrectly for a crank that is reground to BSA specs.

So Drunkenmonkz, Don't toss that crank anywhere, get yourself another set of inserts from someone besides Hepolite and try them.
1 member likes this
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