Which engine

[BaldyTone]

Hi, I have recently got a traveller, and am trying to check the timing, but I'm not sure what engine it is, I know it's been changed to a 1098, but don't know if it's high or low compression! There is no engine number on the block or the log book. I have had the head off to replace gasket, and the top of the pistons are convect. Thanks in anticipation. Tony.

[RobThomas]

http://www.minispares.com/product/Class ... 0to%20shop

IIRC, they come in circa 3cc and 7cc dishes for the high and low comp.

[BaldyTone]

Cheers Rob, do you know of any external way of identifying it, the trouble is I'm not sure of the timing figure! On reading the manual it states set 4deg B.T.D.C on low compression engine and at tdc for high compression engine, "an alternative setting for high compression engine where high grade fuel is not available is 4deg A.T.D.C " seems a bit funny having it after T D C. Cheers Tony.

[philthehill]

As regards the timing ignore the manual timing settings as the petrol composition is not the same as when the manual was written.
As a start set the ignition timing at 3 degrees before TDC. Road test and advance the ignition until the engine starts to pink/knock and then retard until the pinking/knocking disappears at all engine loads.
As each engine is an individual item the timing has to be set to suit the engine not the manual - the quoted timing is only a base setting which has to be adjusted to suit.

[RobThomas]

Do you have the 5-digit number off of the side of the distributor? That is almost MORE important than the depth of the pistons as it will change the maximum advance position. Engines are identical so no way to tell from the outside.

[philthehill]

The number on the side of the distributer will not tell you anything other than what distributer is fitted.
As there are high (40849B) and low (40899B) compression distributers (type 25D4) fitted to the 1098cc engine - unless you know the engine number which will tell you whether the engine is high or low compression it cannot be safely assumed from the distributer number that the engine is either high or low compression.
As the engine has been changed from I presume 948cc to 1098cc the 948cc distributer may have been retained as it will physically fit and work as it is also a 25D4 type but of course it will have different advance characteristics.
The main difference between the high and low compression distributers is the amount of advance at any particular revs.
The low compression distributer does not advance as much as the high compression distributer at the same engine revs.
Unless you have high compression and low compression distributers that you can interchange and road test and the engine is in perfect condition whether it be high or low compression - to me there is little point in being concerned as to what distributer is fitted.
I would suggest that you use and get the best out of what you already have.
Whilst all 1098cc Minor engines are physically the same - high and low compressions aside - they do not all run the same and that is why the final timing should be determined from road testing the car or even better on a rolling road.

[RobThomas]

My thinking, Phil, was that if you ignored the pistons and merely set the timing to give a suitable timing setting at high rpm then you can work out a starting setting based on the max advance that the dissy baseplate gives you. Would that make sense? If the baseplate has a small max advance then setting it as if it were one with a large advance would make the static timing vastly wrong at high speed.

Something like "Ignore the pistons, ignore the static timing and get it right at driving speed"

[BaldyTone]

Thanks guys, great help, I shall do as you both suggested.

[philthehill]

Rob
Looking at the data in the wksp manual - the difference in advance at 4000rpm is very little whether it be a H/C or L/C distributer.

H/C dizzy...................25 - 29 degrees plus 3 degrees static at 4400rpm

L/C dizzy....................28 - 32 degrees plus 3 degrees static at 3800rpm.

Whilst a slight difference I do not believe the difference is so much to cause a real performance drop.

So getting the engine running well at speed with the distributer as fitted should be not difficult - just advancing or retarding the timing to suit the engine rev range. A bit time consuming but will give a good overall performance without spending any money.
Phil

[RobThomas]

OK, Phil. I agree.

I hadn't realised they were so similar in the settings. Lesson learnt.