AAZ engine knock

[chrisbeck]

Hi
on a recent trip back from France the AAZ engine in my T25 developed an engine vibration/knock. Luckily we made it home and the problem didn't get any worse.
Last week I decided to remove the sump, and found what i thought was the problem, No 4 main bearing cap had snapped a bolt and was laying in the sump, so removed the bearing cap expecting much carnage but to my surprise no damage to the crank or bearing. Whilst getting ready to bolt the cap back up it broke in two, never seen that before.
I scourced another cap and some bolts from a freind, checked all the other caps and bolted it all back together, and have been putting some miles on it.
The problem is that under load there is still a vibration/ slight knock, not as bad but it is definitely there.
The crankshaft pulley end bolt is tight and was replaced when I did the conversion, it's running the JX exhaust manifold with new turbo, brickwerks oil cooler, lower temp t stat and has run faultlessly for the last four years.
My only thinking now is could it be the thrust bearings causing the crank to shuffle, ( I STUPIDLY DIDN'T CHECK THIS WHEN I HAD THE SUMP OFF).

Any ideas would be well received people.

Thanks

[syncroandy]

Aren't the caps line-bored with the crankcase ?

[chrisbeck]

Could be, but had no choice to use another cap, bearing fit and fit to block is good with the replacement cap.
It's now a chicken and egg situation, did the broken bolt cause the vibration in the first place, or did the vibration/knock case the bolt to break.
Vibration is less than before but def there.
I should add that I think someone has rebuilt this engine in the past, as all the rods are dot punched in cylinder order.
What do you think about my thrust bearing idea Andy?

[davegsm82]

Did you get a chance to check the other bearing shells while you were in there? losing number 4 completely would put more immediate stress on 3 and 5, not to mention the crank. It may be that the lower caps on 3 and 5 have worn so you are getting a knock on flexation of the crank.

Would likely be worth checking the others just in case. I had a failed number 5 bearing in a newer engine and you could see the knock-on effects all the way down the crank (as well as enough movement to cause the oil seal to fail), but it had been run like that for some time (before I got it).

Dave.

[chrisbeck]

Althogh I should have known better, I just checked the torque of the other caps. Kicking myself now, but was elated to find something so obvious at the time, plus was using my mates business with a hoist so was on a bit of a time crunch. The plan now is to rip the sump off again, look at all the other bearings, and go from there.
I have had a bit of luck as a freind has just given me his old AAZ for a case of beer, so if push comes to shove I will be giving that one a freshen up and hopefully getting it fitted before we go to Italy in it in August.