Author Topic: Possible bent crank aaargh! (Read 4430 times)

MikkiJayne · « **on:** July 11, 2007, 08:36:57 am »

Hi everyone,

I'm working on a Corrado TDI conversion using a 97 AHU engine. It's all in and running but I have 2-3mm runout on the crank pulley :? I've tried a pulley from another engine and that does the same thing, so the only reason I can come up with is that the end of the crank is bent and causing the runout

I have no idea of the history of the engine as it came from ebay with no accessory pulleys on, but the crank sprocket looks original as the bolt is nicely rusted to it. I can only think that the donor car had some sort of front/side impact that smashed the pulley and damaged the crank?

Any thoughts or suggestions would be very welcome, as I think I'm going to have to find another engine :evil:

Tia, Mikki x

Doug · « **Reply #1 on:** July 11, 2007, 09:51:30 am »

When you say bent, do you mean that the pulley wobbles from side to side or radially around the axis of the crankshaft? If it is from side to side then dressing the end of the crankshaft with a file may help the pulley to mount up square. It is possible to straighten a minor bend in a press. You would have to remove the crankshaft to do that. Generally any impact heavy enough to damage a crankshaft has probably broken the casting holding the journals so an inspection tear down would be a good idea to find out out what you have really got.

MikkiJayne · « **Reply #2 on:** July 11, 2007, 11:47:07 am »

Radially round the end of the crankshaft, like its not on properly. I've done some more investigating since I first posted...

I have about 0.5mm runout along the line of the crank, measured at the outer edge of the crank sprocket, and about 1mm front to back, measured on the end of the sprocket bolt.

When I put a pulley on it ovbiously exaggerates any wobble as it's much larger.

I've got the sprocket bolt loose though, so I'm going to take the belt and sprocket off next to have a look at the end of the crank.

There was nothing broken or bent on the rest of the engine (pas pump, timing belt covers, etc) so I'm not sure what's happened. The engine only has 88k on it and is otherwise in great condition. Starts really well ironically :roll:

Mikki x

Doug · « **Reply #3 on:** July 11, 2007, 12:04:03 pm »

You need to measure the crank with no sprocket on it. That is bare. The way you describe this situation it sure sounds like the sprocket and its attachment is the issue.

myke_w · « **Reply #4 on:** July 11, 2007, 12:21:11 pm »

perhaps the timing gear is loose? perhaps there a piece of dirt or rust in the fast of the gear that causes it to runout?

clean the fact of the gear and rear of the pulley. Also be sure you are installing the pulley hole over the proper nub

MikkiJayne · « **Reply #5 on:** July 11, 2007, 01:05:28 pm »

Well I've taken the sprocket off and the end of the crank is pretty mashed

there's a large lump of metal at the edge of the keyway which is probably what is causing the wobble.

Unfortunately that leads me on to another problem...

Having cleaned up the end of the crank someone has definitely been rather unpleasant to it. The housing has a couple of chunks out of it, and the keyway is a bit of a mess. This is a later design with a flat on the nose of the crank rather than the traditional slot, but the sprocket has about half a tooth of play in it now :?

Doing the sums this means I have 2 degrees of variance in where I can put the sprocket relative to the crank.

So... a, does this matter much? and b, should I go for 2 degrees forward or backward?

Thanks!

Mikki x

myke_w · « **Reply #6 on:** July 11, 2007, 01:39:05 pm »

you need to have the crank welded and made to fit a tdi style sprocket.

MikkiJayne · « **Reply #7 on:** July 11, 2007, 03:25:21 pm »

It is a TDI :?:

What do the updated ones look like? I thought thats what this is?

jtanguay · « **Reply #8 on:** July 11, 2007, 03:36:42 pm »

well either way this will need to be repaired. the only way i can see that happening is from a huge shock load... an accident maybe? when you install your alternator, make sure to get the one way clutched pulley (the rotating mass of the alternator can actually put back stress on the crank when you go from a high rpm to a low rpm and the alternator is still spinning fast.

seems like the snout should be welded and machined. wonder if it's doable while in the motor...

good luck

MikkiJayne · « **Reply #9 on:** July 11, 2007, 04:48:29 pm »

This is the sprocket:

The crank is the right shape, but worn by about 1mm or so, allowing 2 degrees of play in the sprocket location.

I don't actually know where in my 2 degrees of movement is the right place though, so not sure where to weld to fix it :?

Mikki x

bigblockchev · « **Reply #10 on:** July 13, 2007, 06:34:00 pm »

This would appear to be the same issue as the AAZ crank keyway fix. Solution pull crank, weld crank, machine crank. If you have it welded just have the flat put on the opposite side from the original. I just did this for my AAZ lots of work , pull engine, flip over on engine stand, pull oil pan, loosen rods and mains, remove crank. No need to remove head or Inj pump. Hardest part was finding a machinist who would do it, most were afraid of welding cranks (935 racer did mine thanks Dave) Search posts for "AAZ crank pully" for pix to show your local machinist. Cheers Dan

Author Topic: Possible bent crank aaargh! (Read 4430 times)

Doug

Doug