MB5 2 Posted January 16 Share Posted January 16 Hello, I have a 2015 dct with 48000 miles on it, will be doing a oil and filter service soon and checking valve clearances etc. What figures for engine compression tests should I be getting? What would be good readings? Link to post
Rocker66 34,437 Posted January 16 Share Posted January 16 Hi MB5 welcome to the forum . I’m sure somebody better qualified than me will be along to answer your question. Would yo care to tell us where you are located ? Link to post
Slowboy 20,447 Posted January 16 Share Posted January 16 Hello and . The manual quotes 257psi, at 450 odd revs (starter motor speed?) anything over 220psi should be ok. If you join as a member (via the donate button to Ted) that might help your need for a manual 😉 Hope that helps anyway. Link to post
jeremyr62 2,557 Posted January 16 Share Posted January 16 Holy crap, that's high compression. My old VF500 was around 125 psi on a good day. Link to post
Slowboy 20,447 Posted January 16 Share Posted January 16 1 hour ago, jeremyr62 said: Holy crap, that's high compression. My old VF500 was around 125 psi on a good day. I thought that as well. As a working figure I’ve always used anything over 135 to 140 psi is ok. I’ll have another look in the manual, but the figure is as I’ve stated. Link to post
Slowboy 20,447 Posted January 16 Share Posted January 16 (edited) Page 1.8 of the manual “Cylinder compression at 470rpm - 1,775 KPa (18.1 kg/cm2 257psi)” no service limit specified. The same figure is given in chapter 10, page 10-6 compression test. higher than I’d expect but there you go, it’s what the manual specifies. Edited January 16 by Slowboy Link to post
Xactly 5,394 Posted January 16 Share Posted January 16 I wonder if it’s because the motor is long-stroke ie doesn’t rev much but the piston travels a long way relative to the bore size. I suppose also that modern bikes with EFI generally run much higher compression ratios than in the past. Certainly 9:1 on an old Brit bike is on the high side. Or perhaps it’s because the reading is taken at 470rpm? Who knows, but it seems high. Whatever, piston ring/ valve wear is rare on these bikes anyway 1 Link to post
jeremyr62 2,557 Posted January 16 Share Posted January 16 Diesel engine territory. Explains a lot 6 Link to post
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