Pulled out my engine today

[RaceDiagnostics]

Killing time this morning before heading to the machine shop to pick up the CAMs.

Starter motor and solenoid bolted back together.

Need to sort out a couple of new screws there.

The full engine rebuild gasket set wasn't as full as it could have been, so cut out a couple of new gaskets.

Oil pump damper back together.

Then off to pick up the CAMs. The left CAM perfectly on the target size. And rotates perfectly with all the cam towers bolted down.

The right CAM is not so good news, it has had the leftmost two journals ground (1 and 2). The far left is perfectly on size at 49.275 but the next one in is oversize at 49.28, however even with that there should still be a bit of clearance if everything was concentric. When I tighten down tower 2 (with the others already tightened down) the CAM shaft binds up (worked it out through a process of elimination). It's no big deal and I am sure the machine shop will be able to sort it out, but they are now closed till next Monday so I will have a bit of a delay.

 

[RaceDiagnostics]

All's well that ends well.

We can assume that new set of bearings from Mercedes will be concentric.

We can also assume that there may/will not be concentricity between two different sets, regardless of whether they are the standard size or undersize. This can be deduced from the fact that Mercedes will only sell a full set.

So mixed sets will have the chance of not being concentric.

When fitting a new undersize bearing set, you must grind all the journals at the same time on the same set up to ensure concentricity.

If you only grind one or two you are guaranteed to have some amount of non concentricity between the journals.

What happened to me was very unlucky, I ordered (from ebay) what I thought were 3 good standard size bearings that turned out to be undersized, non concentricity factor 1.

As a consequence I needed to grind 3 journals on the CAMs, non concentricity factor 2.

The only machine shop I could find that was open (covid) was one I said I would never use again, non concentricity factor 3 as well as grinding one of the journals over size.

From that it is clear that I would be very lucky to have no issue with binding, and I'm not that lucky, so this is what I did today.

Blue up the bearing.

Bolt it down.

Give the CAM a half twist and review.

Then use my contraption with 400 grit emery and a scotch pad applying pressure where needed (yes I know I lots of people will say DONT USE A SCOTCH PAD!) to get rid of the binding spot. It took 5 iterations to get the CAM to rotate smoothly. The bearing was cleaned each time till there were no traces of sanding material.

All done, almost.

Once that was complete I also did a bit of work on the other two bearings with the blue to ensure they were also running perfectly.

 

[Melvyn Best]

That’s a perfect example of something that should be line bored with the bearing carriers bolted to the head

 

[roofman]

I would check again once the heads have been nailed to the block...just incase any torsional twisting has occurred on the heads, very very slim chance but better safe and all that

 

[RaceDiagnostics]

Yes, you are correct, I will check and adjust again if necessary once mounted to the block.

 

[RaceDiagnostics]

All the new bolts organised for the rebuild.

I was surprised to see that the pistons sit proud of the block at TDC, given there is no recess in the head, that's cutting it close with the thickness of the head gasket, the spec says 0.75mm max projection.

Head ready to go on.

Head in place.

Various brackets and starter motor heat shield held on with head bolts.

Out for a Covid lockdown walk.

New chain guides and sprocket, with head torqued down, the CAM shaft still rotates smoothly!

Other head sat in place, initially I thought "great, the chain meets up as expected", more on that later.

Next a quick check on the timing marks at TDC, left head (from the front of the engine), good.

Right head, good.

Looks like the timing spike on the aftermarket water pump is a bit off, as I know the engine is perfectly at TDC.

So the problem is, the chain is too tight or too short, this is the post on the chain tensioner rail, it should be recessed in the head about 1 or 2 cm. Now I have still to torque down the head but I cant see that giving much more slack! Confused.

The chain is a Febi which should have 198 links which is correct, but I didn't count them.

I'll need to get an endoscope in there tomorrow to work out what is going on.

 

[RichardM]

Check the bottom cam chain drive to ensure there are not three chain pins on two sprocket teeth, have you rotated the engine all the way round?

 

[RaceDiagnostics]

Just ran out of time today, I expect to find something like that tomorrow.

 

[RaceDiagnostics]

Well it's been a frustrating morning, I linked the chain and pulled it all the way through, no issues, used an endoscope to check that all the cogs were meshing properly with the chain and counted its links, all was correct. I also checked the number of links on the old chain, it was the same.

I plan to link and pull through the old chain next, but don't expect it to be any different. Then I will have to take off the timing cover and maybe the heads in order to not damage the gasket to check on the new sprocket dimensions.

The new Items are, crank sprocket, idler sprocket, cam sprockets, chain and chain guides.

Any other thoughts?

 

[Melvyn Best]

Has the tensioner piston moved out ?

I vaguely remember having problems with a Mercedes timing chain tensioner, spent ages trying to fit it but had a similar problem to you. In the end the tensioner piston popped out from the main body, I then found there was a ratchet in place that meant the piston would only move in one direction, fitting the piston in from the opposite end of the tensioner cured the problem

 

[zx9]

The new Items are, crank sprocket, idler sprocket, cam sprockets, chain and chain guides.

If the sprockets and chain are identical to the old ones which I think you said they were, how about the guides? They did look very different to the old ones or were the old ones really not so worn as they looked and the new ones are not correct? Don't know I have done a few Japanese four cylinder bike engines and push rod car engines but nothing like what you are working on here.

 

[RaceDiagnostics]

Frustrating day!

This morning I rotated the engine and pulled the chain all the way through, no snags, pile ups or problems, just went straight through, so there was no issue with the way the chain was threaded trough all the sprockets.

The tensioner is spring loaded and also works off oil pressure. With the chain linked there is no way it will bolt on. Its not a ratcheting tensioner.

I then connected and pulled through the old chain.

It was the same as the new chain, it linked up as long as the tensioner rail was in the wrong position.

So there was no choice, slacken off the heads and remove the timing cover and the upper chain guides. I put the tensioner in place, you can see that the chain is one link too short.

Tensioner peg pushing against the tensioner rail peg.

Next I measured and compared the new sprockets with the old, they were close to identical, I quick comparison of the lower chain guides came up with nothing obvious.

Tomorrow I'll start swapping back in the old parts till I find the problem.

 

[Milkybars]

Gutted for you, one step forward and three back.

 

[RaceDiagnostics]

It's weird, I put in a new chain in ten years ago with no problems at all. There must be an issue with one of the new parts or I'm doing something very stupid!

 

[roofman]

Has the tensioner some form of valve inside it to stop it drawing back on engine shut down..In other words what stops it going slack with no pressure behind it given you said it has no ratchet

 

[RaceDiagnostics]

It's got a stiff spring in it to take up the tension during cranking, then oil pressure takes over. This is how it all fits together.

 

[roofman]

It's got a stiff spring in it to take up the tension during cranking, then oil pressure takes over. This is how it all fits together.

Are the components inside the tensinor the right way round

 

[RaceDiagnostics]

Thanks for the suggestions, but in this case it's never been opened and is new, and looks identical to the old one.

 

[roofman]

Thanks for the suggestions, but in this case it's never been opened and is new, and looks identical to the old one.

does the old one draw back further into body then

 

[Migmac]

Great thread