Very tight upper timing chain

[Chris24]

Hello,
I am in the process of reassembling my engine and fitted a composite payern headgasket that is slightly higher than the metalic ones. It may not be the only reason, but my upper timing chain is very tight. It was hard to put the sprokets back on the flanges of the camshafts and and bit of leverage and hammering was necessary. Now the chain is tight to the point were it’s so straight that depressing it is nearly impossible. The question is: should I leave it this way and wait for the chain to wear a bit or should I fit the metalic headgasket + maybe ordering a new chain ( mine is “uprated”) to have a bit more initial slack…
Of course, I have set the chain tensioner to its best position to give the chain a bit more length.
Thank you!

[Chris24]

What I have done is check the torque on the cylinder head nuts, and made a few turns of the engine to screw the sprockets to the camshafts and lock wiring the screws, and now I can press the chain with a finger and see a bit of slack. So I have decided to leave the composite headgasket. With heat, the chain will expand, and wear a bit. At least it will not rattle!

[rfs1957]

Something doesn’t quite add up here.

Changes in the thickness of the head gasket are derisory in relation to the potential eccentricity of the adjuster, just as the tightness of the clamping torque would essentially make zero difference to chain tension.

In my (albeit limited) experience the chain can be made pretty slack, and as most of our engines will have had head and/or block skimmed at some point, I can’t be the only one to wonder whether my eccentric actually had the scope to get the chain tight enough.

I would swallow my pride and ring Rob Beere before I started this engine up.

[mgcjag]

I have read this befor on JL..fitting composite gasket on head that hasn't Been skimmed the sprockets not fitting.. levering and banging them on is not the solution..Neither is running tight hopeing that the chains will slacken..fit the correct thinner gasket and check out the adjuster...search JL for more info..Steve

[Chris24]

Thank you Rory and Steve for considering my problem, your opinions are very interesting.I precise that the flange of the camshaft was so close that it was levering the sproket and giving it a few taps with a soft nylon mallet.Not banging it with a sledgehammer! I have read the post on JL, and that’s a fact, my block was lightly skimmed, and that’s why I have gone for the composite gasket. There are a few places were a bit of pitting can be seen and I thought I would be safer with a gasket that probably seals everything better. Could the initial compression ratio have something to do with the height of the head ( and therefore the distance for the chain to reach the sprockets? ).My head id a 9:1. Just trying to understand that issue!

[Chris24]

I have searched a bit more and a new type of eccentric shaft should be used ( ref C27189 ) when using a thicker headgasket…

[mgcjag]

There are 2 tensioner.. one for a 3.8 and one for a 4.2...if you fit a thicker head gasket to a 4.2 and the chains are too tight then I think you can fit a 3.8 tensioner...C27189 is I think the later 4.2 tensioner...what engine/ head do you have..3.8 or 4.2....Steve

[Chris24]

Hello Steve, I have 3.8 original engine block and head.

[Chris24]

I just checked on Barrat’s website, and 3.8, 4.2 s1 and 2 use the same eccentric shaft c27189.
Could it be that those new shafts are made with a little bit more offset? I doubt about it…

[mgcjag]

SNG website says that the 3.8 one (C2177)is no longer available and they give an alternative that they say is suitable...unfortunatly SNG are not engine rebuilders so you need to do your own checks.....Steve

[rfs1957]

Ring Rob Beere.

[Chris24]

Thank you Rory, I may email them.