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MG TD TF 1500 - Crankshaft Run Out

This is a Heads-Up for those rebuilding engines. I finally got around to rebuilding some of my XPAG TD engines after gathering up enough parts to do so.
I decided to use the MOSS rear Seal Conversion on one of the engines because the crankshaft oil scroll was obviously in poor shape(scored and well worn). In checking dimensions and clearances for the seal, I decided to set up a dial indicator to check crankshaft run out of the rear flywheel flange OD. With the crank resting in the block main bearings, I was surprised to find that the flange had almost.004" run out when the crank was turned through one revolution. This was a crank that had been previously turned.020/.020" and came out of a running engine. now .004" doesn't sound like much but when one considers that the flywheel will be attached and wobble that just about kills any chance for a well balanced engine, let alone the forces imposed, besides the new MOSS seal will use this surface with a Speedi-Sleeve. To confirm my finding, I checked run out on other crankshafts I had for other engines. Two(2) out of four(4) had flange/oil slinger run-out of several thousandths. The common denominator was that the ones with this run-out problem had previously re-ground mains by different machine shops; and the ones that were standard and had not been re-ground were good with no(o) run-out. I took the bad ones to a machine shop that builds billet racing cranks. They were able to correct the run-out by re-grinding the mains to the next under size, reestablishing concentric center line. According to the owner of the machine shop, my crankshaft mains had been previously ground off center due to poor attention to detail when the crank was chucked in the crankshaft lathe during earlier re-grinds. BOTTOM LINE If your crankshaft has reground main journals, check the run-out of the oil slinger and flywheel flange OD because no rear seal system will work with this problem, and your wasting your money to have the crank balanced with a wobbly flywheel.
Richard Cameron

Rich, just to satisfy my mind - you are measuring on the crankshaft, not the run out at the outside (ring gear) edge of the flywheel. Right? Bud
Bud Krueger

Yes, just the crankshaft flange itself at the outside diameter. It was clean with no marks or flaws.
Richard Cameron

Another note: After discovering my potential problem, I contacted Lawrie Alexander who advises MOSS on their Rear Seal Conversion kit. He said, he would submit a recommendation that MOSS update its instructions to include a check for flange run-out because it would account for potential leaks. I haven't seen this update yet though.
It was a disappointment that I had to have my crank main journals reground to correct the problem because it meant loss of precious metal and new bearings.
Richard Cameron

What a pain. difficult to check insitu, I wonder if the nose can be used to check somehow, od is much smaller ...
mog

Rich, W.K.F Wood states a TIR limit of .002" as shown below. Is that the same measurement that you are referring to? Or, is he referring to the edge of the flywheel? TIA. Bud


Bud Krueger


I'm not talking about run out of the flywheel clutch plate surface. What I'm talking about is the crankshaft flange outer surface where the Moss conversion seal will ride. I believe W.K.F Wood is stating the total dial indicator reading (T.I.R.) limits of the flywheel clutch surface.
Richard Cameron

Richard, as it happens I'm dealing with a very similar issue right now. I had installed the older Moss kit at my last rebuild and it leaked badly. The engine is apart right now and like yours, the flange of my crank is not round. However mine is not off center like yours, but rather suffers high and low spots which suggests it was never machined accurately.

While this can certainly affect the sealing capability of the kit, it shouldn't make any difference to the flywheel since it is located by dowels, not by the outer surface of the flange. But in your case I can see how it would be a problem!

The bottom line is, even with a perfectly centered rear flange, it may not actually be round.
Steve Simmons

Rich, this seems a rather stupid mistake to make in a machine shop, to offset a crank in a faceplate? is the nose offcenter to start?
I would think even on a smaller od of a nose the run off of .004 would be the same as diameter has nothing to do with it.
mog

Mog, I'm getting use to stupid mistakes by machine shops. I've seen several lately. In this case though, it was done incorrectly by more than one machine shop in the past on different cranks. Setting the crank properly in the lathe and checking to confirm concentricity is one of the first basic step in regrinding the mains. If its off center, all further operations are also off.

My guess is the nose would also be off too, but harder to measure with the key way and scratches from pulley installations. However, I did check the oil scroll on one of the bad cranks and it matched the .004" of the flange in run-out. Seems that our engines don't always receive the respect they should as a precision piece of equipment by all machinists.

From this experience, I would bet there are many more cranks out there with the same problem and causing untold leaks, vibrations and such. Like I mentioned earlier, my cranks were fixed by a machine shop that specializes in crankshaft manufacture. They confirmed the run-out I found and were able to correct it.

Steve, I would think the machine shop could carefully re-grind your flange OD to remove the high spots if they aren't too bad. However, the readi sleeve has a 3.740" minimum limit so they can't remove much metal.
Richard Cameron

You would be surprised how many machine shops, even crank grinders, can't do anything with the rear flange. I don't understand why. I found only one who said yes.
Steve Simmons

This thread was discussed between 30/03/2015 and 31/03/2015

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