Herald 13/60 Compression Pressures

[PeteH]

Hi

 

Quick one here. What should the compression pressure be when tested with a gauge?

 

My old Gunson Gauge is showing 1) 235psi 2)215psi 3)230psi 4)230psi.

 

These seem somewhat high? but are within a 10% tolerance.

 

Pete

[Clive]

compression testers are not really a calibrated instrument, so the actual readings are not that important (within reason!)

If yours are all that close, I would be happy.

 

I presume that was with wide open throttle. Have you repeated but putting a teaspoon-ish of engine oil in each cylinder? That can be informative. 

[Pete Lewis]

and  done on the starter  with all  the spark plugs out ,,  !!

 

those figures imply you have a CR of nearly 16:1  more suited to a diesel

 

Pete

[Steve P]

Very high i would have thought,my car runs 10:1 and that was about 180psi when new.

Steve

[PeteH]

Hi.

 

MY thoughts are that the Gauge (40+yrs old) needs recalibrating!.

 

I expected about 130 to 160 psi. The engine is on the bench and the test(s) performed using a freshly charged battery, plugs out, first run "as is" second run with oil in the cylinders, I suspect the "low" reading may be due to valve leakage rather than rings. I plan now to have the head off anyway, mainly to check if the head has been converted to "unleaded" status. at which time I will have a look at the bores.

 

I have a 12/50 manual, which shows the Compression pressure as circa 136psi. But I was looking for the 13/60 figures. which would /could be different?.

 

 

Pete

[Pete Lewis]

Unleaded work is generally just hardend exhaust seats and a tougher valve

Inlets are ok as is .

And compression results tend to be atmosppheric pressure x the CR

 

eg 14.7 x 9 less any inefficiencies

 

 

 

pete

[Colin]

Hi Chaps;

My Swiss chum came over with his compression tester. Took out the plugs and turned my 1147 Saloon on each cylinder. He's now gone so I can't ask, but whereas your figures state psi (?) My cylinders were measured as follows;

Cyl 4: 10 Cyl 3: 10 Cyl 2: 9.5 Cyl 1: 10

Does anyone know what units these would be?? 

Best, Colin 

[johny]

They would be Bar where one equals 14.5psi so your readings look pretty good...

[Colin]

I think I have answered my own question . . . I think it's 'bar' . . . ? Am I correct? 

And, that those numbers stack up to be quite reasonable?? 

[Colin]

Thanks Johny! Needed that corroboration! 

I am amazed - given it's the original engine on 143k miles. I've always regularly changed the oil, though! 😉

[johny]

Yes that is good especially if the head hasnt had any valve work either...

[Colin]

Ah; well . . . When the Gov began to alert us that 4* leaded was to disappear, I took advantage of swapping to a John Kipping (ledge!) unleaded head. That was decades ago! So clearly the hardened valves and seats have done their work, too!!😉