Compression figures

[eben80]

Hi guys,
I've just done a compression test on my engine out of interest. Readings were 119 psi & 121 psi.
What is the "normal" range?

Thanks & regards

Eben

[smallcox]

Hi Eben,

If the compression ratio has not changed than 140psi would be a good reading, those figure if correct are too low. I would expect the engine to run but you will get blow pass the rings and cause a positive presure in the crank case which will show itself as oil blowing pass breathers and seals .

Is the gauge correct do you think

[jokke]

I got about 165 PSI on my engine. but I have change all the gaskets and pistons rings.. so I think is to low as smallcox says..

[eben80]

Thanks for the replies guys. It is a cheap gauge but I suppose the crankcase pressure would cause the valve in the oil cap to by wheezy as it is. I've got the head off at the moment to change pushrod tube seals (someone used ONLY silicone sealant  ) Is it possible to change only the rings & sleeves if needed without disturbing the crank?

PS: I haven't had smoke while driving, only a puff when starting.

[smallcox]

If your happy the gauge is reliable, the valves where sealing ok in the cyclinder head then now would be a good time to change the bores and rings. you can get over size rings and have your bores machined to match or buy new cyclinders. not sure of prices these days.

Anyway if you remove the sump with the engine in the car and undo the big end bolts on the conrods then the whole assembly will slide up the studs. Air cooled it take it?

[eben80]

Hi yes, its an aircooled. I'm a bit hesitant to do work on the crank as I'm not familiar with the process of measuring the journals, replacing bearing shells etc. then again I'll be replacing the sump gasket anyway so I might as well check for excessive play while down there.

126fan has the whole cylinder, rods, rings, pins & piston kits for EUR 186 but I will check the valves & rings first.

[smallcox]

I have striped many engines and the journals do not normally suffer from wearing oval, the main thing is that there not heavly scored. Fitting new shells to the conrods is advised when assembling the rods to the crank again and the cost is low for this and dead easy as you will see when you remove the old ones.

 On the back of the shells once removed there should be a indication of there size, ie original or -20,-40,etc. you will need to order the same size to replace.

[eben80]

Thanks for the advice. So what you are saying is that unless I see obvious wear on the journals, I should just be able to replace the bearing shells with the same sizes that came out?

[smallcox]

YES

[eben80]

Good stuff. Thank you.