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Please Help, lost two crank pulley's

3K views 11 replies 6 participants last post by  ShaneB 
#1 · (Edited)
I've done practice this morning and on lap 6 or so I heard a hell of a noise, this was my first crank pulley coming loose. This engine has done a few races already so it can't be something that could happen cause of bad assembly. The marshals later showed me the pulley and it looked like it broke off. I then got some new parts (new pulley washer with the bite out) fitted it and bend the washer.

Now, how can I loose the pulley again in just about three laps ?

any ideas how this could have happened? (twice)?

Racing again tommorow, hope you guys can help
 
#3 ·
I had one bust on my Mazda truck just idling at a light. just kinda herd a clunk and the alt light went on. and the pulley part was on the ground, and the rest was tight on the shaft.

Did you have the old one piece or the newer one with the damper?
and how much balance holes were in it? (i had one that I was scared to use as the balance holes seemed too extreme)
As you will not have a balanced set now anyways I would use the one with the damper
as they can auto balanced a tad. and if you have some sort of crank ringing going on, it should snub it.
 
#4 ·
Gordon Raymond has some small diameter aluminum engine pulleys that are intended for high revving engines. The purpose is to prevent high rpm damage to the alternator and cavitation in the water pump.
 
#5 ·
Not sure that relates to Shane's problem here? It is not uncommon for the stock pulleys to crack around the key way. But it doesn't usually lead to a complete failure. And having two let go so quickly points to some other problem. I was also wondering if the woodruff key might be missing/damaged, but I would think that would just lead to slipping on the crank nose, not a broken pulley. Please report back when you discover the problem, so the rest of us can learn from your misfortune!
 
#6 ·
race 2 completed no incidents

Last night we had a good hard look at what could possiby have happened and could not come to any conclusive answer. Woodruf key looked ok

Pulley 1: (right hand side) looked like it has physicly broken around the key (it was picked up from the tarmack so could have broken from the fall and a few bounces on the track) BUT this morning I got the other pieces Pulley 2: from the inside of the engine compartment -so no boucing on the track as thought and they don't fit on pulley 1



So before Saterday's morning race we were back at the track at 5am (waking some of the motobike guys that sleeped there the night) we re-alligned the alternater (someone suggested a mis-alligned alternated can cause this! I dont agree but tried anything at this stage) torque to 150 pounds with locktide on the threads.

Completed race 2 without any incident!

but the question remains how do you loose two pulleys so soon after each other? Both broken around the key!
 
#7 ·
My guess is the crank is ringing or some sort of out of balance that is stressing the pully.
it might be good to also check the clearance on the main bearings the next time you have the bottom open before you change bearings or rebuild.

How light is the flywheel? if it is superlight the pully might be acting as a flywheel too.
Is the key way tight? I would use a new one anytime something like this happened.
If the keyway got hammered it might have some play and the pully might start bouncing back and forth until something breaks. Also check the crank to see if the keyway is larger then it should(I would think the harding would keep it in spec) but something is up.

And one last silly thing. Check that there is no way any thing can smack the pully.
fan blade, crossmember, etc. anything that might hit when the motor flops about.
 
#8 ·
just noticed looking at you pic. There is no way it should have been able to get off the crank with just that much missing.

was the nut missing or still on the crank?
was all the parts installed including the washer?(105.50.02.104.00)
did the nut bust? in the pic the nut does not look anything like (105.50.02.105.00)
 

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#9 ·
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was the nut missing or still on the crank?
was all the parts installed including the washer?(105.50.02.104.00)
did the nut bust? in the pic the nut does not look anything like (105.50.02.105.00)
Your picture is from an older crank - my crank is from a later 2000l with extruding tread that fits my pictures nut (36 mm) with the washer with the 'bite' out of the inside hole.

The first pulley's nut is missing and the seconds is in the picture (that I found inside the cars engine compartment)
 
#10 ·
I wouldn't rule out two cracked pulleys. A surprising number of front pulleys develop cracks over time. I hadn't thought much about this until I checked a couple I had and discovered that both had cracks in them. As a result, I bought a degreed pulley from Classic Alfa to use on my 2 liter build.

Pulleys aren't something most people check but we should remember that these are usually 30 or 40 year old pieces and have seen quite a lot of use.

It's good to know that Gordon has new pulleys. Wes Ingram and Daron Walker (Vintage Customs) also have degreed pulleys avaliable.
 
#11 ·
So in both case the nut came off. I am guessing you problem is the nut. when I have had them break the nut and center is aways on the crank.
I would say the nut comes off then the pulley starts to walk out and starts to wobble then breaks.
So are the threads OK both crank and recovered nut? might want to condenser using safety wire

Also does that pulley match the year/type of crank? could the nut bottom out while the pulley is not tight?
and hard to tell with the pic but it looks like a very thin nut. does that have the treads to hold a race motor?

But in the end if the nut is not on the crank when it was over the problem is the nuts.
did you fold the washer on to the flats of the nut after it was torqued?
(going by memory here) but I think the washer is bent to the flats. at lest most cars do that. might want to add a keyed tab washer to bend on the flats. or do the safety wire thing or both.
if the threads are trashed that is a other story. but still a fastener problem.
 
#12 ·
update

just an update

ive done a couple of races now without any issues , must have been the nut and probably having a different thead that spun off with the washer at high revs
 
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