M110 2.8 Straight Six Cam chain problem...help!

[ddentrec]

I am rebuilding my W123 280TE; the engine has had a top-end rebuild, including a new duplex cam chain. The engine is still out of the car.

New cam chain is the original MB £££ part, 140 links, exactly the same length as the old one (I double checked before I started!).

So, imaging my confusion when I find that I now cannot put the camchain tensioner back! It seems that the chain is effectively too short = chain is already tight before the tensioner has even been replaced = tensioner being pushed too far away from chain = cannot bolt tensioner to cyl. head.

Now, I'm not stupid and have rebuilt many engines before. The timing sprockets are all aligned OK, tensioer has been reset, timing is spot on, all chain guides & guide rails in place, no kinks in the chain, engine can be manually turned over with no tightness.

Is this a one off or is there something about the M110 straight six I am missing?? Any advice appreciated.

 

[Ian B Walker]

Not meaning to teach a granny to suck eggs but are you sure that its routed properly and that the chain goes through one of the guides and not round the outside?

 

[ddentrec]

Hi Ian,

I will do this tonight: I will eyeball everything. Will even put the old chain back as a diagnostic if needed. It was 12.30 AM when I gave up yesterday...a fresh approach will most certainly help.

Thanks

 

[grober]

Mb Manual M110 Engine ( W116 Series)

Heres a link to the official MB manual on the m110 engine. Hope this helps.
http://handbook.w116.org/engine_77_2e.htm I think you might be into offset woodruff key territory here but not sure.

 

[ddentrec]

Thanks for your help so far!

Old cam chain is about 4mm longer than the new one (normal wear I expect).

If I put the old chain back then tensioner fits 100% OK.

If I put the new chain back on then the tensioner still does not fit!! £$%&!!

I have checked the guides, sprockets, tensioner, timing and can't work it out (but then that is the fun in rebuilding cars, right?!)

Will give it another go tomorrow. If that does not work I will contact the W123 owners club in Germany. But clearly I am doing something wrong here.

Thanks again for your help.

 

[stargazerplus]

Does this engine have the same tensioner as the M104? Have you reset it before installing?

 

[grober]

parts diagram

THERES AN EXPLODED PARTS DIAGRAM OF THE TIMING GEAR HERE.
http://www.detali.ru/cat/oem_mb2.as....400&VIN=*&CT=M&cat=032&SID=05&SGR=001&SGN=01
They list the roller chain as part no 0009976994 and list 4 offset woodruff keys to change timing by 2,3,4,5 degrees.

I would also echo stargazerplus' comment see http://handbook.w116.org/Engine\110\05-310.pdf I know you said you reset it just checking.

 

[ddentrec]

Does this engine have the same tensioner as the M104? Have you reset it before installing?

No, this has the later type that does not require a reset.

I will re-check and double check. I know I have made a mistake somewhere. My conclusion is that the chain is simply not the correct size: it may be the same length but the effective chain height of each link must be too much = makes the chain 'fatter' than it should be. I will check with a vernier gauge tonight....thank again for your support.

 

[stargazerplus]

Don't understand how your tensioner wouldn't need reset. Yours cannot be a later model as the M104 engine came later. There are various stories about tensioners not being reset after a chain replacement and the chain snapping due to being overtensioned.

 

[ddentrec]

Don't understand how your tensioner wouldn't need reset. Yours cannot be a later model as the M104 engine came later. There are various stories about tensioners not being reset after a chain replacement and the chain snapping due to being overtensioned.

According to the info I have ( and feedbabcak from www.w123.de), the 'early' M110 tensioner required dismantling to set it to its starting point. My M110 is of 1984 vintage, and the tensioner is of the 'later' hydraulic type according to the diagrams I have (and does not require resetting).

But anyhow, I am seeking your advice here, and am happy to consider any reasonable suggestion. So, I will dismantle the tensioner and reinstall it.

Thanks again.

 

[ddentrec]

Grober and stargazeplus: your were both right--I did not properly reset the hydraulic tensioner assy. I read through the on-line service guide and all is now perfect!!! Tensioner is now fitted correctly...I was being stupid!

Thanks for your help!

After the engine is complete, the next steps will be the get the bare shell professionally re-painted...

 

[grober]

Sorted

Glad you got it sorted. These tensioners are trickly little bu--ers! :bannana:

 

[stargazerplus]

Yes well done. Haven't done this before but I was sure that this was the problem!