Distributor timing on older machines.

I've got my BN back together (thanks, ScottyHOMeY on the head bolt question, that was simple enough) and it seems to be running well.

Since I've been running this machine it's had a bit of skip (chuff) on high idle. Since I had it in the garage to replace the head gasket I deiced to do a full tune up (obviously the valves lash since the head was off, plugs, wires, went through the carb etc).

After all that I still had the skip so I finally loosened up the distributor and fiddled with it until it smoothed out.

Since the BN doesn't have the timing marks that the later machines that came with distributors is this pretty much the best the best method for getting it "right"? I know you can cause heat issues if you have your timing to far retarded (which is what I did, retard the timing that is). I'm guessing, these things are to finicky but I figured it wouldn't hurt to ask.

Thanks,

K

The "B" DOES have a "TDC" mark and after measuring the circumference of the flywheel it will be EASY to make a second mark @ about 25º or 28º and check if the distributor is advancing the timing into that range @ high idle.

(quoted from post at 18:00:17 09/06/09) The "B" DOES have a "TDC" mark and after measuring the circumference of the flywheel it will be EASY to make a second mark @ about 25º or 28º and check if the distributor is advancing the timing into that range @ high idle.

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Well, I didn't think about that but then again with out splitting it that's not going to be the easiest thing in the world (that little view hole doesn't give you much space to work). What would you use as a static make to align with?

It would be a bugger laying under the bell housing and trying to adjust the distributor at the same time. Then again maybe I'm just a wimp.

K

> What would you use as a static make to align
> with?

You"ve got the head off: use top dead center.

Getting it to TDC on #1 -- with the obvious proviso of putting your thumb in the hole to make sure that you're coming up on compression, top it out by eye and then use the trick of putting a stiff wire or short screwdriver in through the plug hole to make a lever of it. When the outisde of your lever is at its lowest, the piston is at its highest. Ta-da!!

To fine tune/verify that with the mark on the flywheel, take a toothbrush ( a similar-size brass or sttel brush is better) with your favorite solvent to find the mark, then hit it with a squirt of brake cleaner to dry it off and mark it with some paint. The index will differ according to what kind of half-moon cover you have under the motor at the front end of the torque tube. If it is cast, there is a nub/fin on the inside of the casting. If it is stamped, the vertical rib stamped into it is your index.

If you are feelin' wimpy, this is a great opportunity for personal development, and you'll be a better man for it (JK!). If you've got it close enough to find the mark and paint it, it shouldn't take more than a dive or two underneath, with trips back up front to the fan in between to turn the motor to get them lined up. There is nothing wimpy or unmanly about removing all the plugs to make the motor easier to turn. ;8^)

Sorry. I didn"t read closely enough: I thought you still had the head off. In any case. Scotty"s got it.

Simple,

Get a digital timing light with a tach in it.

Hook to #1 plug wire and power source. Run tractor to full throttle and turn dist tell you get max rpm [ on tack] and lock it down.

Remember how old it is, things have gotten sloppy over the years so setting to factory marks may not give full or expected power.

(quoted from post at 18:56:00 09/06/09) Getting it to TDC on #1 -- with the obvious proviso of putting your thumb in the hole to make sure that you're coming up on compression, top it out by eye and then use the trick of putting a stiff wire or short screwdriver in through the plug hole to make a lever of it. When the outisde of your lever is at its lowest, the piston is at its highest. Ta-da!!

To fine tune/verify that with the mark on the flywheel, take a toothbrush ( a similar-size brass or sttel brush is better) with your favorite solvent to find the mark, then hit it with a squirt of brake cleaner to dry it off and mark it with some paint. The index will differ according to what kind of half-moon cover you have under the motor at the front end of the torque tube. If it is cast, there is a nub/fin on the inside of the casting. If it is stamped, the vertical rib stamped into it is your index.

If you are feelin' wimpy, this is a great opportunity for personal development, and you'll be a better man for it (JK!). If you've got it close enough to find the mark and paint it, it shouldn't take more than a dive or two underneath, with trips back up front to the fan in between to turn the motor to get them lined up. There is nothing wimpy or unmanly about removing all the plugs to make the motor easier to turn. ;8^)

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OK, I left my self open to the wimp bit.

I guess what I'm asking is there anyway to verify the high speed advance timing (30 deg ATDC @ WOT)? The only way you can do it is with a ATDC mark and a timing light.

Now if the distributor is set correctly at slow speed, it should be right at high speed too if the distributor is working properly.

Rummaging through my manuals I found the the book that came with the distributor (1973 is when it was upgraded from a mag) and it sounds like you time it at TDC statically, no timing light option.

At TDC, with the switch on you should see a draw on the meter (points are closed).

Oh and as far as indexing, did that twice today. Set the valves, after reinstalling the head, warmed her up, re-tourqed and did it all over again. I'm almost a pro now!

I guess if it's running bad at WOT with the timing correct then there's something wrong with the advance.

I'll take a closer look tomorrow.

Thanks guys,

K

(quoted from post at 19:10:28 09/06/09)
Simple,

Get a digital timing light with a tach in it.

Hook to #1 plug wire and power source. Run tractor to full throttle and turn dist tell you get max rpm [ on tack] and lock it down.

Remember how old it is, things have gotten sloppy over the years so setting to factory marks may not give full or expected power.

Click to expand...

Stupid question, isn't that more or less what I did only I used my ear instead of a tach?

K

You could try that.

I don't know how much you're willing to fiddle with it, but we're trying to get rid of the skip. If you've got a helper to turn the distributor while you shine the light up underneath, here's some numbers.

Full advance on a B/BN is with battery ignition is 40 degrees. I don't have a flywheel laying around, but I just went out and measured an old ring gear and did some arithmetic. The flywheel diameter is close to 10-15/16". Multiply by pi and divide by 9 (40 out of 360 degrees) and you get a little over 3-13/16", not a whole 3-7/8".

If you wanted to mark that off, it would be to the right of your TDC mark as you sit under the tractor looking to the rear. That would be your mark to line up with whichever type index you have. It's tight quarters, but can be measured and marked off if it's worth the effort to you. Just paint it a different color from your TDC mark.

Two things to keep in mind. Your timing train will be a little sloppy from wear, as James Rumpf points out, so none of this (beginning with my close but not precise measurements) is going to be completely accurate, but would serve as a rough guide. The slop is more of a problem with static timing.

Which gets to the second point, which is that timing at speed is with no load and the slop in the gears floating. Even attaching a PTO implement like a bush hog won't help much as they will float, too, once up to speed. The only way that comes to mind right off to tighten up the whole timing train under load is on a dyno. But if the bottom end of your motor is reasonably tight, you should get a reading close to the 40-degree mark when up to speed.

Bottom line, I'd set it up on the static mark and see how it runs. If that gets the miss out of it and the tractor works like you want it to, great. If not, then you might try marking off the 40 degrees and checking it with a light to see where you are -- just remember you're dealing with paint dots, and a couple of degrees aren't going to make or break your miss. If it's close to 40 on the light, then you've got other, easier issues to check out. Some could be really basic -- weak coil or condenser, dirty points, burned cap or rotor, bad wire or connection . . . Others could be tougher, like a worn distributor shaft (making it wobbly so that it throws the points out of time -- your mark will jump around a lot or skip a beat when running under the light)

It reads like you took the ribbing in the right way. I couldn't resist. (We Talers have to be careful when we venture onto serious boards!)

On more serious issues, you're saying advance, which is BTDC, B for before. A(fter)TDC retards, but it's clear you're thinking in the right direction.

Yes, by rights, on a tight engine, static timing should give you the right advance at speed if the advance mechanism is working correctly.

But as James Pumpf points out, you'll get slop in the timing train with wear. This occurs primarily between the crank and cam gears, and cam and governor/distributor drive gears. That will cause the advance mark I described in the post above (q.v.) to float but stay in visible range. Because small turns made with the fan blade act on the crank gear, they won't show up by resistance, but you can sometimes detect that kind of slop with some clicking/clacking sounds as you rock the fan back and forth.

If you're able to mark off the 40 degree advance mark and find yourself in the ballpark on running timing, though, I'd address other possible, electrical weaknesses in the system first, but you can't eliminate the possibility of worn shafts in the distributor. IH put plugs instead of zerks on the lube points for them, because they don't need much grease or often, and I guess there were problems with folks not reading the book and pumping a grease gun on zerks until grease came out somewhere, at which point they had pumped the distributor body full of grease (not good). The payback is that with the plugs, a lot of them never got lubed and have worn until they are out of round, which would cause your timing light, at running speed to skip, as opposed to the mark just floating a little.

See my post above.

Correct,

I run a tractor Dyno for money and fun so i see the slite differances changes make.

The older cubs that were rated at 9.8 hp were factory set at "said" rpm. Now turn them up 2-3 hundred rpm and watch the differance. Look at the NE specs for the newer ones . There is also other factors here, but point being it's still just a C-60.


My point is you can't here the differance. I just did a tune up on a little Massey a few weeks ago and timed it this way with great results , there able to brush hog with less rpm .

The rpm effects the advance weights inside the dist. The springs from the factory are "very" heavy and i'm not really sure at what rpm they open if at all.

I put chevy recurve kit springs in my dists to get the advance open sooner. [light] on the Super M.

Take the time to try it this way, you will be happy with the results. You can buy timing lights on line cheap that have the Tach feature just make sure it is digital.


Jim

OK, I think I'm following you guys.

I'm still not sure how I would be able to mark the flywheel with out spliting the tractor. I can just barley get my hand in there, never mind be able to see what going on in there with my hand in there!

The only thing I could do is make a static mark some where on the front of my tractor and then make my own TDC & 30 deg mark on the crank pulley. That might not be quite so hard. Oh and I see you say 40 deg ATDC @ WOT, all my books say 30, maybe that's WOT under load?

I like the timing light with a tach idea, the only thing I worry about is if I do have slop in the drive system and I get the high idle zeroed in what that's going to do to my low idle timing. Using this method I'm assuming it's best to have the machine under load? I don't have a dyno but I do have some PTO implements that would at least give it a bit of a load.

Maybe I'm just being to picky. Can I really do terrible damage to an engine that WOT is 1400 RPM by being a bit off with the timing? Really, all I want to do is get rid of a miss.

I'm going to time it statically, see what that does for me, then go from there.

Oh, and I enjoy a little humor!

Thanks,

K

No you won"t hurt it at 1400 rpm ! If you turn up the governor speed to high you will.

Keep in mind there is only "3" main caps on that crankshaft. There is also "no" bob weights like a car crank so to much rpm will kill it.

Example...

On a "M" motor, a stock cam runs out of power around 1900 rpm. After that the torque #s fall off very fast.


You don"t need alot of rpm to make good power.

If you're confident you've got it at TDC there's nothing wrong with, in fact there's a lot to be said for, making some handier marks on the front pulley.

Re advance numbers . . .

If you've got the original motor in it and you can find a code A stamped onto the distibutor body, advance is as follows:

0 at stop to 400 rpm
19 at 800 rpm
34 at 1200 rpm
40 at 1600 rpm
Full tilt no-load rating for the motor is 1540, that pulls down to 1400 under load

If you've got a motor from a SuperC or a late Super A, (from the motor serial number) and you find a code J on the housing, the numbers in the same order and at the same speeds are 0,9,24,30. That may be where you're getting the 30 number from.

The 30 number is from my 200 manual so that makes sense. The sheet that came with the distributor doesn't have advance numbers, just a basic "this is how you install it".

So...I got everything back where the book said it should be at TDC and guess what, it skips, I retard the timing a bit (turning the distributor clock wise) and it cleans right up.

I'm not really sure what I should do. If I run it where the book tells me to it doesn't run all that well (it's not like I loose a cylinder, it's just a miss every few revolutions), if I run it where it sounds good I'm out of time.

Could there be something simple I'm missing here?

Maybe I'm over thinking and should just go with what works...

Thanks,

K

That could be just that slop in the gears. If it doesn't run hot where you've got it set now, I'd call that good. Did the engine speed seem to slack off any when you retarded that bit?

No, it was quite constant, at least by ear.

Just because it only takes me a few seconds I reset everything again just to make sure I didn't mess up at all the first time and I got the same results.

The distributor shaft has very slight play in it, I'm not sure how tight they're suppose to be, it's not sloppy, just ever so little play back and forth.

I'm going to be doing some plowing this week, which will be the first work this old girl has seen in a bit. I'm going to start at factor spec and see what happens. If it continues to miss, I'll retard the timing a bit until I get something that works. I wish I had a temp gauge, then again if I see steam I know somethings wrong!

I guess I might end up chalking this one up to 60 year old machinery.

Thanks again guys for all your help, I wish this had a bit clearer outcome.

K