Engine Rattle

[datty240Z]

I'm getting a light rythmic rattle on the over run and also when the revs are falling back down after reving the engine in my '74 240Z. It sounds like its coming from no1 cylinder. I thought maybe a piece of valve had broken off and was rattling round in there. I lifted the cylinder head off but no evidence of anything untoward. Anyone got any ideas what it could be?

Thanks.

[datty240Z]

Actually its probably more of a chuffing noise. Could i be getting blow by on the ex valve sticking or not closing properly whe n not under load?

[Rob Gaskin]

To your first post I would have said examine the timing chain and tensioner.

To the second I would have said check the manifold sealing - have you got a 'six-branch'?

[datty240Z]

I originally thought a blow out at the manifold but it seemed ok (before I removed the cylinder head). How do I check the tensioner, do I have to remove the front cover? Would it make this sort of noise then? I have a block of hard wood holding the tensioner in at the minute.

[datty240Z]

I don't have a 6 branch, just the standard ex manifold.

[Rob Gaskin]

Originally Posted by datty240Z

I originally thought a blow out at the manifold but it seemed ok (before I removed the cylinder head). How do I check the tensioner, do I have to remove the front cover? Would it make this sort of noise then? I have a block of hard wood holding the tensioner in at the minute.

Well tbh I'm not sure how to check the tensioner if you are holding it in place, however is the nylon guide that the chain runs on ok. Is the chain badly worn? Do you have a workshop manual for reference?

[Rob Gaskin]

Originally Posted by datty240Z

I don't have a 6 branch, just the standard ex manifold.

Well the standard manifold is less prone to sealing problems.

Was the spark plug tight?

Tappets clearance ok?

I'm just thinking out loud really.

[datty240Z]

Plug was tight and tried setting the tappets before removing the head. TBH Im swayed towards the chainchain tensioner

[datty240Z]

Ok, so today I removed the front cover, chain and tensioner. The chain looks to be in good condition but it seems to have munched through the nylon tensioner to such an extent that it has started to gouge a groove in the steel base of the nylon part of the tensioner at its leading edge.

Also when I tried a trial reassembly of the chain and timing marks it would seem that the chain has stretched so that I should be using the no2 timing marks instead of the no1 ones on the camshaft sprocket.

Could the combination of these 2 have caused my strange noise? I hope so cos I can't find anything else wrong.

[ddhchp]

Hi
Here is somthing to look at take of the valve cover and look all the way down to the crank journall. There you will see a SKEW gear my one was cracked causing the same noise in the same area. Easy Job remove the pully remove the seal and remove the gear and replace it and the drive shaft for the oil pump and dizzy. Not an expensive job watch the timing though.

Best Regards
Dean Halsey

P.S. get Classic Sports car next volume my Z should be in it up against a 3l gxl Capri

[datty240Z]

Thanks for that. I already have the head, front cover and pulley etc off so I'll get a look at it tomorrow.

[Rob Gaskin]

Originally Posted by ddhchp

get Classic Sports car next volume my Z should be in it up against a 3l gxl Capri

Yes I know