Bighorn Crank/Aux Pulley Troubles

[Fredward]

Hi there, new to the board, having some fairly major difficulties with my girlfriends 1992 3.1TD Jap import Bighorn. It's one of those cool Lotus spec ones which drives like a racecar

Anyway, she's owned it for about 18 months and already spend $3000 NZD on repairs/servicing. Not long after she bought it, after driving up a big hill she noticed the engine seemed to make a nasty whinging noise at higher revs. She drove it to a mechanic who originally diagnosed it as a turbo fault, then thought it was poorly tensioned belts, so adjusted them and fixed an oil leak.

Not long after it started making the noise again but this time was very noisy and the engine was not under heavy load. She took it to her local mechanic who then diagnosed it as the auxillary belts pulley on the crank, he thought the bolt was shot, and replaced it - he decided to do the timing belt too as there was no record of it being done in recent history. Then after driivng it home a few weeks later it happened again when reversing a fairly weighty trailer up a steep driveway. The noise was pretty bad and didn't know if it was the t-belt on it's way out so we had it towed to her mechanic, he admitted that he replaced it with a second hand bolt and then charged her again to replace it with a new bolt. A few months later it started again.. The noise was obvious but not unbearable. Sick of dealing with it she put it to the back of her mind and eventually it went, big time.

I had to go out and rescue her as she lost power steering etc. I saw all the belts were off but not snapped.. Urgh. The timing belt light was on but the engine ran fine. We were close to town so drove carefully it into another mechanic whilst watching the temp guage closely! He found the very broken pulley at the bottom of the engine bay.. So before this gets fixed again, I want to know if it's possible/probable that the end of the crank is out of line/bent which is what throwing the pulley out. I thought it was most likely the mechanic not correctly torquing the pulley bolt up but find it hard to believe that two mechanics (the one before she owned it and the other guys) have got it wrong. Obviously it's going to be expensive to fix, don't want the same issues to arrise. Otherwise... Rebuild? Engine transplant? Or just do what we want to do which is strip it for parts?

[geeves]

This problem is not as uncommon as it should be. The normal senario before hand is that a mechanic replaces the timing belt but on the pulley there are 4 small bolts and one large bolt. You should never undo the large bolt but instead undo the 4 small bolts. This is different to most engines. The large bolt should be torqued to 152 foot pound which is nearly impossible without removing the engine. After a while the bolt comes loose if not torqued correctly. Behind the pully there is a spacer and the timing belt pulley. These are held in place by the large bolt and have a keyway in them When the bolt is loose these can move which wears the keyway allowing them to rotate slightly on the shaft. When this happens any attempt to replace the bolt without replacing the spacer and pulley will probably fail. Sometimes there is also wear on the crankshaft as well. At best you need to replace the spacer,timing pulley and fan pulley. If the timing cover is worn this should be replaced. It is also a good idea to get the crank inspected for wear. This can be done without further dismantling but should be done by a very good mechanic.
How long does it take to happen?
On mine the bolt fell out 70000km after a belt change. Once the bolt falls out all that holds the timing belt on is the tension on the fan belt. I was lucky

[Fredward]

I finally got round to looking at this with the idea that I could set up a steel plate bolted near the crank and turn it over to see if the crank is turning evenly or in al elipse but even at first sight I can see the keyway was damaged from when the pulley flew off. Will this need a regrind and will my above theory be sound?

[geeves]

Will need to talk to an engine re conditioner about this. If the keyway in the crank is damaged then it will need to be built up or recut it a different place. Not possible with the crank in the engine but they may have some other method I dont know about. Only other option is a second hand engine or a crank from a broken engine