TS185 ER compression ratio
 

Hello Hubbers,

I have a question about the compression ratio on my 1982 ts185. Stock it is 6.2:1. If atmospheric pressure is approx 14.7, i should expect to receive approx 91psi from a cylinder compression test, right?

When i test it though, i actually get 125psi. I've tested the compression gauge on an air compressor (it monitors the pressure leaving the tank), and it appears to be reading accurately. That would suggest that i have a compression ratio of approx 8.5:1.

Am i calculating this correctly, or am i missing out on something (a brain perhaps :confused1:)

Cheers, John.

That's a good question John. I'm going to cross post this on another forum and see if I can get any answers for you.

regards

Nigel in NZ

Thanks Nigel :)

If its any help, my 74 ts185 gets 122 PSI on the compression tester, so it would seem normal to me.

As for the ratios, I haven't a clue.

Ed

Yeah, it sounds like 120-130psi is a normal sort of reading. Thanks.

Calculate compression:
Compression=P0*C^^1.4
P0=Pressure at TDC (14.7 PSI)
C=Compression
1.4=Ratio for air

Your bike
C= 14.7 PSI* 6.2^^1.4= 189 PSI

But you will never get that high, parts of the stroke doesn't contribute to compression.

Thanks AliBaba! There was more to it than I thought. It's reassuring to know that my engine hasn't been 'stroked' - if it were I'd be in all sorts of trouble with timing, jetting, lubrication etc. Thanks for the handy info!

Compression
 

Well im gettin 140 psi out of my 84 TS 185
John