Engine question 7:1 or 8:1??

Hi

I need to set the timing on my 67 series 2A but I'm unsure as to weather it is a 7:1 or 8:1 engine. The engine i have in is not original it is an ex-military one. Is there an easy way of telling what it is?

Cheers
Rob

Hi,

Compression gauge? The problem you will have is that an old engine may have been skimmed... You could set the timing using a vacuum gauge, that's how I generally do it.

Sorry novice question.
I have a compression gauge but im not sure how to use it can anyone steer me in the right direction.

Thanks
Rob

Take all the plugs out, screw it in da hole and turn the engine over a few times with the starter motor. Assuming your gauge has a max reading and it's not one of these you have to look at all the time. You should get out of the cab to find a reading. I don't however know what reading you are looking for.... Normally you use these things in a diagnostic manner to see if all the cylinders have the same compression, etc. Not sure what pressure you want from which compression ratios, and it will change a bit with engine wear....

Thanks, im not sure what reading im looking for i read that it should be 150lb ish and that if one was different by 100lb then a tune up wouldnt help..
How do you set the timing using a vaccum gauge?

Rob

There should be a 8 stamped on the head under the inlet manafold if its a 8:1.
Have a search on here for 8:1 and there was a thread the had all the details.

For example a compresion ratio of 7:1, means 7 times atmospheric presure, so atmospheric presure beeing 14.7 psi,

A 7:1 compresion engine should give a reading of 102.9 psi and a 8:1 compresion engine should give a reading of 117.6 psi.

set yer dizzy at 6° BTDC. then wiff the injun running slowly turn dizzy anti-clockwise till its has slowed down. now turn clockwise till it just starts to speed up. losk th edizzy there and yer ign. is now timed to suit YOUR engine.

That is basically how you do it with a Vacuum guage, you back off 1/2 inch of mercury. The gauge gives you some more diagnostic info too, but same idea.

fooking vaccum gauge.. just use yer ear bestest timing tool there is

You know one of the things that makes this site what it is is the delicate and sensitive political skills you can learn from slob. As I sit here I can just imagine a bloke sitting in a shed with an old SII sipping tea from a china cup, little finger extended in pristine overalls. In the background there is a bloke ****ing in his toolbox, that's our slob...

i would just like to point out that its not MY toolbox am is ****in in

That cant be slob!
A real landy owner would be drinking from old EP90 tin and ****ing on his neighbors BMW convertible.

Lazy Landy said:

For example a compresion ratio of 7:1, means 7 times atmospheric presure, so atmospheric presure beeing 14.7 psi,

A 7:1 compresion engine should give a reading of 102.9 psi and a 8:1 compresion engine should give a reading of 117.6 psi.

Click to expand...

the compression ratio is the swept volume plus the headspace added together then divided by the headspace.

that is not strictly true
it depends on whether the pistons are dished, flat or have valve cutouts and whether the head is dished or flat.
strictly speaking it is the ((combustion chamber space+swept volume) divided by the combustion chamber)

Indeed; when I said headspace I meant the volume of the mixture at tdc.