• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Engine rebuild B204 "The rabbit hole"

Waar rijdt deze 940 rond ?
Deze wil ik in echt eens zien !
grtz uit Vlaams brabant !
 
dafke said:
Waar rijdt deze 940 rond ?
Deze wil ik in echt eens zien !
grtz uit Vlaams brabant !
Click to expand...
NOT A 940 :cry:
IMG-20240407-113524763-HDR.jpg


Thuis in Oost-Vlaanderen
 
Last edited:
It looks at least one of the cams locked up and the crank kept going and shredded the belt.

I wonder what was the root cause of failure... Maybe the timing belt jumped time relative to the crankshaft and then the valves got munched up and locked the cams. Can you turn the crank or either of the cams?

EDIT- My 1990 740 GLE started whining from the front of the engine bay today. I immediately parked it thinking about reading this thread today.
 
Last edited:
Mistakes were made. It looks like the dowel of the belt tensioner pulley was poorly installed, causing a slight misalignment of the tensioner arm and resulting in the belt being worn away by the arm.

IMG58.jpg

IMG60.jpg


The belt has lost around ten teeth on the crankshaft side, and the engine will no longer turn over.

I suppose I’ll have to blame the mechanic for this one, oh wait, that’s me. :shutup:
 
Lankuu told me that he often sees bent valves on the inline 5 and 6 cylinder WB engines; replacement valves are all that is needed in MOST cases per his experience. Hopefully there is no cylinder wall damage.... your pistons were +1 OS and new, as well as the bore to match? I hope you can repair the head/valve damage and return your 960 to operation. Good luck, these things can happen to even the most fastidious mechanic.
 
Lots of debris on top of those pistons. Condition of cylinder walls? Does the crank still rotate freely or is there binding?

Can't tell from the pics, but is there piston damage at the ring land areas?
 
Last edited:
DET17 said:
Lots of debris on top of those pistons. Condition of cylinder walls? Does the crank still rotate freely or is their binding?

Can't tell from the pics, but is there piston damage at the ring land areas?
Click to expand...
There are some scratches in the cylinder walls. The pistons are very indented by the loose valves. crank rotates free. I don't think the crank is damaged. The head on the other side...
 
So the BOLT that the tensioner pivots on backed out? It looks like it pulled out so far it was rubbing against the camshaft gear.

I don't understand how the pulley is damaged like that.
 
Yeah that is belt dust.

It looks like the cast metal arm that holds the tensioner pulley went forward due to a loose mounting bolt. The pulley was leaning forward, and the rear edge of the pulley became a timing belt shredding knife.

I am confused, did TWO bolts come loose? The pulley bolt AND the mounting bolt? The pulley bolt should have never been touched since it is part of the tensioner assembly.
 
Last edited:
Gerrit said:
Mistakes were made. It looks like the dowel of the belt tensioner pulley was poorly installed, causing a slight misalignment of the tensioner arm and resulting in the belt being worn away by the arm.

IMG58.jpg

IMG60.jpg


The belt has lost around ten teeth on the crankshaft side, and the engine will no longer turn over.

I suppose I’ll have to blame the mechanic for this one, oh wait, that’s me. :shutup:
Click to expand...


Basically, HOW DID THIS HAPPEN? That bolt should have never been touched.


Also, can you please do me a favor? What are the belt sizes/part number on your accessory V-belts? I got 11mm by 1295mm off the alternator and 13mm by 1194mm off the power steering. (sorry to ask in a blown engine thread. too soon?)

Hopefully you can find a replacement engine.

This thread made me tear into my engine tonight for a peace of mind. Mine is an OEM replacement engine installed in an unknown year (with a timing belt done in 2023 sticker). I found a KOYO bearing and an AISIN tensioner.


TimingBelt11.28.jpg
 
Last edited:
ZVOLV said:
Basically, HOW DID THIS HAPPEN? That bolt should have never been touched.
Click to expand...
As far as I know, the complete tensioner unit is no longer available; I was only able to find the bearing.
During assembly, something went wrong, the bushing got crushed, and the bearing was therefore crooked.
The bolts were not loose.
 
ZVOLV said:
Also, can you please do me a favor? What are the belt sizes/part number on your accessory V-belts? I got 11mm by 1295mm off the alternator and 13mm by 1194mm off the power steering.
Click to expand...
For the alternator/water pump i've got a V-belt 1288mm x 11.9 #969474
The other 2 for power steering and airco : 1175 mm x 13 mm #978397

Maybe different for the B234 engine? I don't know.

​

 
You must log in or register to reply here.
Back
Top