Rattling under pressure

[Phil h]

Hi
just put new head gaskets on and put top end back together set timing at 36 degrees but only under pressure I am getting a rattleing sounds like pinking? Other than that pulls like a train. Any ideas would be great phil

[Sidecarbod]

Sounds like detonation to me, the easy way to find out would be to back the timing right off to something like 30 degrees, the engine will be down on power but if the noise has gone you've got your answer.

[conrod]

Phil,

Wot Pete said! Sounds like dried peas rattling in a can when under load (particularly uphill), but disappears when you back off the throttle.

One thought - do you have a vacuum advance canister on your distributor? If so, you need to disconnect the vacuum pipe (and plug the end with a bolt or something to avoid a vacuum leak) when you set the timing.

[Phil h]

Yes it does have a vacuum canister and no I didn't plug it when I set the timing will revisit that one. Your description is bang on sounds like dried peas in a can. I have today tried rotating the dizzy clockwise and anti clockwise but to no avail. I have noticed the vacuum pipe to the carb is a bit perished would this make a difference ?

[conrod]

Hmmm. As Pete said, backing off the timing by 5 or 6 degrees should have eliminated or reduced the pinking.

You say you set the timing to 36 degrees, which I assume means "all in" with maximum mechanical advance. You should, with the vacuum advance disconnected, have around 15 to 18 degrees advance at idle - what do you have?

Provided the pipe to the vacuum advance isn't split, it should be OK (but worth replacing). If it's split, you'll have a vacuum leak which will cause a weak mixture and a very rough idle.

BTW, to avoid holed pistons make sure you back off as soon as you hear the pinking - detonation will quickly destroy an engine .....

[Sidecarbod]

Yes it does have a vacuum canister and no I didn't plug it when I set the timing will revisit that one. Your description is bang on sounds like dried peas in a can. I have today tried rotating the dizzy clockwise and anti clockwise but to no avail. I have noticed the vacuum pipe to the carb is a bit perished would this make a difference ?

A perished pipe would mean that you are less likey to ever get any vac advance, Like Conrod said, disconnect it when setting up your bob weight timing then reconnect it to the timed port of the carb once you are happy with your setup.

[TINKA]

A perished pipe would mean that you are less likey to ever get any vac advance, Like Conrod said, disconnect it when setting up your bob weight timing then reconnect it to the timed port of the carb once you are happy with your setup.

Disconnect it but make sure you plug it as well.