Tecumseh V70, 1980s vintage

[wristpin]

I’m working on one of the above with points ignition and a 3amp alternator with diode rectification to charge the starter battery.
Before going into a detailed explanation of a couple of issues it would be nice to know if there’s anyone on this forum that either worked on or is still involved with Tecumsehs of that vintage.

[bgsengine]

Ive worked on them yes. they were relatively uncommon, but one I remember most was on an antique Homelite rider mower (circa 1960's in blue)

[wristpin]

Thanks.
The magneto stator holding the ignition and charging coils is under the flywheel and held concentric with the crank by the metal cased top oil seal protruding enough above the top of its housing to engage in a circular hole in the stator casting . This allows for the stator to be rotated a small amount in either direction to set the timing (50 thou btdc) which is the locked by two hex head screws in slots. The points gap setting is 20 thou”.
Unfortunately a metal cased seal of the correct dimensions is not available in the UK. The genuine Tecumseh part is shown on US auction sites but although reasonably priced becomes prohibitably expensive with shipping and UK import taxes, so it has to be a rubber covered one which does not appear to be dimensionally stable enough to hold the stator dead centre.
The first issue is that having set the points gap and locked up the stator screws and refitted the flywheel the some of pole pieces of the ignition and charging coils rub the inside of the fly wheel . It then becomes a trial and error / hit and miss job to centralise the stator without rotating it and loosing the timing - has to be done blind as there’s no way of “ seeing through the flywheel” or using setting gauges.
The next issue is that the ignition cam is machined into the crank - no removable cam ring . So if it is worn , it’s new crank time. I have the Tecumseh Mechanic’s Manual of the era but there is no mention of that, let alone any dimensions for checking for wear.
So having taken all that on board and having the points set at the recommended 20thou” and the piston at 50thou” btdc the stator is rotated in its slots to get the points to just start to open ( continuity meter) . Nothing! To cut this long story short, the only way to get the points to break at 50thou” btdc seems to be to fiddle the their gap .
By which time the poles are rubbing the inside of flywheel again .
Nightmare ! No wonder manufacturers went over to electronic ignition units mounted outside flywheels where one can gap them and left charging coils fixed inside.

[bgsengine]

OK for one thing, I know what you mean about having them centered, but I cant remember seeing one that needed the oil seal itself to center them - all the ones Ive seen had a raised lip on the oil seal housing, so that is kinda unusual.. But to address the timing issue, The purpose of the point gap is actually to set ignition timing as well (you could alter the old briggs engines timing that same way) so the breaker cam on crank really shouldn't matter.. In other words.. You would set timing at a .020 gap , so that future replacement of points would be set to .020 as well.. so you would not need to re-set timing when replacing points.. if you are not using new OEM points there's possibility of the cam rubbing block being a little too short.. But again, when points are set to .020, one would tend to see points open at the correct time (wear on the cam lobe would be rather obvious, one would think, if it was lobe wear causing the problem) Second point - you may need the spec number because not all engines had the same timing (Some I believe were actually .090 BTDC) Might try .090 BTDC and see if that works out as expected.. One hint as to centering the stator I can think of - if you can get it set to anywhere that nothing is rubbing, then perhaps you can mix some JB Weld or similar hard epoxy, clean and dry the seal and crankcase, then apply (cotton swab) a thin swipe of grease to the stator, and fill the gap, (then scrape excess off stator top to prevent building up a ridge after it hardens) and you might have some luck then keeping stator consistently centered (if the .090 spec doesn't solve the problem when you tighten things down, it might result in a different clearance) ..

Basically it's a rambling thought there but the basics of it, might have to get engine spec number to verify what your timing is supposed to be (and make sure it is actually a V70, not a VH or VM 70? ) and also check your points carefully (rubbing block on breaker arm, the locator pin/pivot on the points, make sure point contacts seat squarely, etc) ..

[wristpin]

Thank you, plenty to think about!
To answer your last comment first. All ID plates / marks are missing . A similar engine supplied to me “ for parts” does have an embossed alloy tag on the back of the crankcase but it is so bashed about as to be of no help. Your comment about the btdc figure had me running to the manual and, yes, the VM has a figure of 0.070.
Interesting about your comment re the location of the stator - makes far more sense, but the spare engine has the same raised oil seal system.
I take on board the “ master class” on points heal wear/ gap setting . As I see it, the btdc setting is the most important even it it requires a divergence from the book points gap, so that’s the way I will go for now.
I’ve got the engine bolted down to a “ test bench” complete with solenoid, battery and ignition switch so now it’s time to play!
Thank you again for your detailed reply .

[38racing]

Not sure if it applies here but I've seen videos where the under flywheel Tecumseh was converted to auto type ignition using abs sensor and HEI.

[wristpin]

The good news is that the engine is running very smoothly on my test bench and as it is going back into a little John Deere that is being restored , just for exhibition purposes, I think that it is safe to say , Job Done!
What I didn’t say in previous posts is that along the way I did try replacing the breaker points with two different brands of electronic trigger module and the engine ran like “a bag of nails” on both!
Thank you for all the suggestions and support .