Octane Rating of Canadian WWII vehicles

[Lynn Eades]

Dan, as the octane rating goes up, the flame front travels faster and so, the ignition timing requires retarding. (not advancing)This allows the piston to reach t.d.c. before the pressure on the piston builds too much.
I'm surprised that Richard F. hasn't chimed in because I faintly recall a discussion about Bedfords and Morris's that had piston problems and I don't recall the reason.

[Keith Brooker]

Found this info from my copy of Supplies and Transport Voll 2, i can put more info from the REME Vol 2 Technical if you want more.
Keith

[Richard Farrant]

Originally Posted by Lynn Eades

I'm surprised that Richard F. hasn't chimed in because I faintly recall a discussion about Bedfords and Morris's that had piston problems and I don't recall the reason.

Hi Lynn,
This subject came up before, I think on HMVF forum, which I participated in. Also on an Axis form, I have lost the links now. The lorries of concern were a batch of Austin K5 4x4 in NW Europe campaign which were having engine problems, apparently with excess bore wear.. The discussions on Axis forum were with non-technical people as I recall (I could only read that forum), but from my research I found that there were a batch of Austin K5's which were supplied for wading, at a guess for unloading from sea transport. These had a special waterproof brake servo. What I did find out from Austin manuals was that the bores were given a greater piston clearance, my guess is that when the engine was warmed up on the landing craft, then plunged into cold water the rapid chill could seize the engine, but of course later on the extra clearance would then mean oil consumption and low compression. If REME were not aware of this they would automatically think that the engines were faulty.
To quote the K5 manual;
"piston skirt clearance has been increased from .0025"-.0028" to .004"-.0045" to make engines with new pistons immediately suitable for wading through water without fear of seizure. Pistons with the original smaller clearance can be used for engines of vehicles which it is known will not be called upon for wading".

Regarding the change to leaded petrol, it was the deposits on valve stems that caused problems and many British manuals gave information on combating the problem, with mods to valve guides, increased valve clearances and alterations to ignition timing. I have quite a bit of tech info on this but am short of time at present.

regards, Richard