The Fordson Tractor Pages Forum

Is 250psi correct?

Hi,

Although I'm not familiar with the p6 engine I suppose 250 psi is far to less. Is approx 17 bar. A sound diesel should be round 25.

Try to find out where your compression goes away. Leaking valves is not a too difficult job and cures a lot sometimes.

Rgds Emiel

Compression:- 380 to 450 lbs. sq. in. Variation not more than 15 lbs. sq. in. Compression of 350 is satisfactory providing variation is within range.

What happened to compression ratio x atmospheric pressure= compression. Which works out at 238 psi .

I'd not thought of it that way before scoobyjim, but having riffled up the compression ratio for the E1a engine at 16:1, have second checked it as correct, (if you disregard the fact that the starting pressure will inevitably be somewhat lower than 1 atmosphere). According to the P6 handbook linked below the P6 is 16.5:1 so around 245 psi

To counterbalance that, the inertia in most mechanical pressure gauges may cause them to over read peak pressure, unless oil damped, in which case it may underread


http://www.fordsonmajor.se/pdf/perkp.pdf may not help much but if you google I'll bet there is a manual for the P6 somewhere.

Happy hunting

Got the manual but there is no mention of compression.

Page 39, settings & data, 6th line down - I assumed those items common to P3, 4, 6 are the lines with a single entry ??

Yes so using the 16.5:1 all we can do is the formula mentioned above which =250

We're missing something important like pressure rise due to the compression increasing temperature (Boyles Law / Charles Law ? ) assuming test gauge is in the injector port there's no pump / injector influence responsible.

With the reduction in volume there is a temperature rise which just using the compression ratio doesn't factor in, as that assumes constant temperature

C'mon Emiel & Barry, put us out of our misery please, are we looking in the right direction, is there a constant or fudge factor which can be applied to the Comp Ratio to calculate the sort of peak pressures that will give an ignition temperature* or are you using figures based on practical experience of this sort of engine ?

*Can't find a pressure value but ignition temp seems to be about 480-500K or 207-227C