Mechanical Advance movement as rpm increases

[oldfarmkid]

Have a 1952 Super- M, running well except when rpm drops below 1100 rpm engine tone is not even. Found from 1100 rpm and above, timing light indicates ignition advance is at full advance and stable, engine sounds the same. At 1000 rpm timing bounces from full advance to about -5 deg from full advance. Below 1000 rpm Ignition timing bounces around as much as 15 deg. Matches sound of the engine. Have new mechanical advance springs on order but have a couple questions I'm not able to find the answers to. Have read Super M advance is up to 40 deg. is that true? Last, is there a chart that indicates rpm and amount of ignition advance for that rpm. Such as 400 rpm 0 deg, 1000 rpm 15 deg, 1400 rpm 35 deg, and so on. Have documented what mine is doing now, and it's not normal.Then realized as often happens, I don't know what normal is. Thanks

Tim

[Jim Becker]

No, the 40 degree advance was with the "A" symbol distributors of the M and other early letter series tractors. The Super M used the "J" distributor that max'ed at 30 degrees at 1450 rpm. The "J" distributor advance was:
0 at 400
9 at 800
24 at 1200
30 at 1450.
If a Super M was upgraded with overbore Fire Crater pistons, it was to have been converted to a "J AB" symbol distributor with a max advance of 22 degrees.

All this information, except the intermediate advance figures, is in the "Engine Tune-up Specifications" Blue Ribbon Serviceman's Handbook in the PDF manuals linked to above.

[oldfarmkid]

In comparison mine is 10 at 420, 20 at 900 and full advance from 1200 on up. Mechanical advance originally crud locked in the full advanced position. Cleaned it up and just snugged up the springs a bit, and at the time was so much better. But now I want the butter smooth running through the whole range I know it should have. Hope the springs do the trick. Well Mr. Becker, thanks much for the quick and accurate reply. Now that I know what normal is, I have a goal to meet. Pretty sure no Fire Crater pistons involved. Also appreciate the Blue Ribbon Serviceman's Handbook reference. When I get a little time I'll get the PDF. I have four or five so far and they are almost solid Gold for a guy like me.

Thanks Again
Take Care
Tim

[John *.?-!.* cub owner]

Check for side play in the distributor shaft that will allow the point gap to vary.

[oldfarmkid]

Thanks John, and of course your right. But your info leads me to a question. Since my timing is rock solid from 1200 rpm and up, do you think that translates to side play not an issue? Maybe the spec. is in the Blue Ribbon Manual I need to download. Just want it to run as smooth as my old H.
Also, hats off to you and your quick response.

[oldfarmkid]

Got my new advance springs from Brillman, and half my problem is solved, Ignition timing is now rock solid at all rpms. Engine now can maintain a smooth as silk tone. But I have only 19-20 deg. full advance. Old springs are two different sizes and weak. There is a #30 stamped on the advance plate.
Take that verifies total advance is 30 deg. Brillman only offered 1 type of spring, so I thought my advance took 2 of the same spring, and I ordered 2.
Called Brillman and they could not find a technician to help. Seems two of the same springs are too strong and not allowing full advance. Could you please supply another good source for the correct springs if my current source can't get what I need.

[oldfarmkid]

Called Brillman back and spoke with a tech. Confirmed many old tractors required two different types of springs. Was told problem is, no one makes the other, looks like weaker spring. He also stated many people are finding the new distributors sold for old tractors have the same issue. They don't get any where near full advance, just like me. He did offer to take back and reimburse me for one of the springs. It won't break the bank so I told him I'll keep it. So, looks like I'm down to the game of cinching up the original weaker of the two springs and hopefully get lucky and find the timing happy place. Will also hit local NAPA and hardware store to see if something close to a match can be found.

[oldfarmkid]

Looks like the correct new springs are at Bates. Solid GOLD $$$

[Jim Becker]

The original part number for a spring package was 358 108 R91. Messick's web site says they have it in stock (less than Bates).

You could try one of your new springs paired up with one of your old ones.

[oldfarmkid]

Hey Jim, Have spent a lot of years working on old motorcycles and have burnt out my desire to mix, match, cinch up old springs to get proper advance response. The shorter response is I've gotten lazy. Just want to buy new springs if available . Mix in a bit of impatience and I've spent a bit more money at Bates. Went to messicks and looked like they also just carried 1 type of spring. 1 new part# and what a misinterpreted as two superseded part numbers for the same one spring. And of course your right, single part number is for package with the two separate springs in it. Bates had a picture of the two separate springs in the package so I knew what I'd be getting.Thats the part where impatience and not waiting till the next day to call messicks cost me $$. Thanks for your response and on point info. Lesson on Old Tractor parts listing learned.

[oldfarmkid]

Glad I went for new correct springs. Timing pulses are steady at any rpm, and have correct advance through out rpm range. Sweet to hear that strong steady exhaust note from idle till full advance.

[oldfarmkid]

Thanks for the info guys. No end play on distributor shaft and rpm / advance movement specs. were valuable information . Guessing engine is original,
think it's now running as close to new as possible. Thats pretty sweet.