piston rings, low compression

[chipysbmw]

Hi all alittle help needed here i think.

Ive a 1977 r100/7 on which i have just replaced the piston rings, left handside only. The piston crown was marked with '94.46' so i put rings that were 0.5mm over size, is this correct? The rings were installed 120 degrees apart and my piston ring end gaps are all .6mm. Thing is, the level of compression has dropped and it wont start on that cylinder. I also cleaned the head, do you think there could be gas leakage through valves to seat, preventing a correct seal, caused by the disturbance or do you think its piston rings at fault.

I dont have the compression numbers as i cant afford that kit right now but, there is a tangible pressure difference between the 2 cylinders when my thumb is used a compression tester!

Thanks in advance to all that can help.

 

[Popell]

Arrr, common mistake, you are in fact suffering from 'perforatis pollice'

Shame, as the rest of your thread sounds like you know what you're talking about - hope you get it sorted.

 

[chipysbmw]

Hi popell,

i dont understand but i fear im a victim of a joke here!

 

[Popell]

Yes, sorry Chips, small attempt at humour, reading the bit "my thumb is used a compression tester" I asserted that you may have a perforated thumb in Latin.
Hope someone can lend some more meaningfull assistance soon.

At least this will bump it back to the top!!

 

[Smug]

Did you fit the rings the right way up? Did you de glaze the bores?

 

[chipysbmw]

No probs, im a bit dim you see popell!

Hi smug, thanks for your help, the rings have been installed correctly and barrel has been deglazed, all be it with wet and dry. Do you know if the rings are correct for that size of piston?

The next plan is it get hold of a compression tester and isolate the head or cylinder via swap over.

 

[chipysbmw]

Hi all, thanks for your help on this one. Just a quick post to update those watching the post past and present.

For those with 94.46 stamped on the piston 0.5mm over sized rings are correct, giving me a piston end gap of 0.6mm, and registering a 10 bar in each cylinder. The rings were spaced 120 degrees apart.