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Help with TD18 no fire


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Guys I've got a TD18 built in 49, it's in good condition. Last fall I parked it and pulled the engine clutch out for a rebuild and now I cannot get it to for fire on gas. I'm getting fuel and spark, it doesn't make sense. I charged the magneto magnet, double checked the timing, took the manifold off and checked the butterfly dampers. While the manifold was off I taped the main intake ports shut and tried a little either directly in the lower ports, still no fire. Cleaned the plugs which are almost new, gapped them also. 

 

This thing has always seemed to not like to fire on gas very well and I've always suspected a weak magneto magnet but that's ruled out now. Also magneto has a new condenser and points. 

I'm at a loss and don't know what else to check, please help! 

 

Thanks,

Mike

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Your problem sounds quite a bit like the one I had for over three years starting my -14.  I always got it going but with an awful lot of grinding on the starter.  One day I had reason to compare the positions of the spark plug wires to my -14A.  They were off one hole on the distributor.  I wired it like the -14A & have not had a problem since.  Maybe a timing check is in order.

Vic

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I had an issue with my TD6 a couple years ago. It ran great on gas then decided to kinda almost run on gas. I had rebuilt the mag a year prior, It was driving me crazy. I would get spark on every plug wire when I pulled them off and got them near ground and it looked great. Id plug the plug wires back on and it would try to almost run. Found out intermittently various spark plugs would get warm then wouldn't. I was thinking to coil was bad so I replaced it again. No change.

I finally borrowed an ignition tester that had a spark plug on it with an air fitting and gauge that would simulate a spark plug firing under compression. Using the gauge on it you would adjust the air pressure to simulate the plug being under compression. As soon as I added a little air the spark would quit. Without air it looked great.

In my case it ended up being the imported condenser. it was shorter than the original so it didn't fit under the original clamp and was supposed to so the case of the condenser didn't contact the mag case for a good ground. Did at first then probably oxidized. I replaced it with the correct one and its ran perfect each time every time.

 

Probably not your issue but that's what happened to me.

 

Good luck!!

 

Ken

 

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Only other thing that comes to mind but probably isn't it, is point gap. If they're not quite opening or closing completely they wont spark. I don't remember the problem but I helped my brother with his Farmall B mag and we had an issue where it "looked" right and he set it with a feeler gauge but it wasn't running or would run erratic, I don't recall. I ended up using an ohm meter across the points to see they were doing their job, and they weren't. It probably had a newer questionable quality set in it I'm sure. That's a lot of the challenge is getting decent stuff these days.

Hope you can make some headway on it soon!

 

Ken

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The list of things to check is long. But start with the simple things first. Check the points. Sand them, but make sure they are clean. No grains of abrasive stuck in there. Then set them. Clean rotor and plug terminals in cap. Have you had the carb apart? Waterloo

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I remember having a lot of trouble with 2 things, well aside from rust on the points, the contacts on the front of the intake, the ones that activate when you pull the gas lever and the coil. 

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Ok. After a different condenser, polishing the points and setting them and various gaps It is firing good while the impulse coupler is engaged. Once the rpms come up enough the impulse coupler drops out then it doesn't want to fire. Perhaps it is firing but too soon, I cannot tell. This is more how it usually acts, always hard to get going after slow rpm firing. There's probably something I'm missing that one of you can identify. Here is a video link. https://youtu.be/tY0_U6DPS-Y

Thanks for the help

Mike

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Well she started. I tried different point gaps and nothing seemed better than around .20 so I left it there. Seems to be back to normal. I don't know if they're all like this where it's hard to get past that low rpm firing, this is the only one old crawler I've been around. I think you just have to feather the choke to get over that hump. After my phone charges I'll put up a full video from start to change over. 

Mike

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Yeah something just isn't right. I don't believe I'm getting a consistent spark. Fires good right away a few times, RPMs come up enough that you don't hear the impulse coupling snap and no fire. As soon as the impulse coupling snaps again it fires.

When I finally managed to get it running it runs great, there's just like a dead spark area at low rpm. There's gotta be something wrong. I probably should get new plug wires too, these are oldies. 

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In these cases you have done all the right things.... but yet something has been missed.

Either something you checked as ok, is not ok... or there is a bad assumption somewhere.

I am thinking timing. Can you describe your timing procedure to us (with detail).

For example I have found slightly different procedures for a TD-18 as for a UD-18. Set mag advanced vs retarded for timing.

Below is for the H4 mag, but gives you some idea of differences. Note the different Angles... you may have a not from factory mag?

MagnetoMarkings.jpg.28f8593f371d4f463f29c6235fe3da66.jpg

What is a serial number of the mag?

Have you not just checked the marks etc, but also wound over extremely slowly and confirmed the impulse does occur on the mark?

 

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James,

 

I'll add a picture of the mag serial number. As far as I can tell it's the original mag but I don't know. It looks like an F6 in the book. 

I set the timing precisely as the procedure in the book states. Which is this basically;

--------------

Remove spark plugs from #1 and find TDC by feeling for compression, continue to crank engine until DC 1-6 mark on flywheel lines up with pointer. 

Disengage the impulse coupling and rotate the magneto to the #1 position. Remove the breaker point cover after fully retarding the timing. 

Rotate the magneto until the breaker points just start to open and then put the bolts in the coupling. 

Replace the timing link on the breaker point cover

----------

The timing has had me puzzled and I have suspected something is off, here's why.  When I set timing per manual instructions then check impulse trips at each cylinder, the mark on the flywheel rotates by quite a ways before it trips. The manual says the mark should never be above the pointer when the impulse trips but it does. Marks 2-5 and 3-4 go past the pointer quite a bit. 1-6 land closer to the pointer. 

At one point lately I tried setting the timing so the impulse was tripping when flywheel marks were at or below the pointer as the book says. I did not have any successful firing but perhaps there was another issue preventing any firing at that time. 

 

There are a couple marks, one on the impulse coupling and one on the part that you bolt it to. These were there before my time and when I follow the timing procedure they line up. And they were lined up before I took the mag off the first time so it seems to be the timing that was used previously. 

 

Something that comes to mind now as I write this is that  when my Dad first got this machine 8 or so years ago I remember him mentioning something about magneto work. Perhaps finding a new one, I don't know what it was for sure. He passed away 5 years ago so I can't ask him what it was. I would suspect he had the magneto off at one time tho. 

Thanks

 

 

IMG_20200330_163508.jpg

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The impulse on the magneto does two things. It gives the mag a quick turn to generate a spark and it retards the timing to keep from kicking back. This is the reason you lock the impulse out when timing the mag to the engine. 

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Your mag serial number has no letters after it, so I assume, but have not reference to check, that it is a 'normal' F6 mag

My TD-18 manual makes no reference to retarding while timing.... My UD-18 manual does say retard. I have been caught by this before. Cost days of tinkering for our UD-18A until we caught it. A different mag on a UD-18? I don't know.

So I wonder if you should NOT be retarding when timing?

Is it still retarded when you wind over slowly to verify? I think during verifying it should be 'normal'. Not retarded.

The fact that it runs verifys mag and fuel etc. It's just down to timing, or maybe the impluse operation is throwing timing off?

td-18A_engine172.thumb.jpg.dfb5477f8c587a8a6efe2aa1a94876fb.jpg

 

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My TD18 manual says go rotate the breaker cover all the way up before you take it off, but from the normal position with the timing link it's almost all the way up anyway so there is very little change by doing this. Not near as much as the action of the impulse coupler by comparison.  Maybe it's enough to make a difference i don't know. Also I have two TD 18 manuals and they both say the same thing for the f6 mag. 

And when I'm verifying the impulse trip I was questioning the marks on the flywheel. The marks are PP 3&4 and PP 2&5.  Are these not dead center marks? I thought I saw somewhere that stands for positive pressure or something?

 

The way that I'm getting zero spark at low rpm has me looking back at the magneto for a problem other than the timing to the engine. 

I'm going to take a couple days off of working on it. Also I have a new condenser coming for the mag, the one I had I don't know if it's actually good or not. 

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Sometimes that's a good idea to take a break from something like this. Once in a while an idea pops up or some one will have another idea.

DWF

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PP 3&4 is the position to pull pistons 3 & 4 out... and you really need it on the mark or the darn things don't have clearance to come out pass the crank and block.

You need the DC timing marks. When you wind over slowly to verify the impulse it should occur on the relevant DC mark

td-18A_engine_pg117_FlywheelMarks.thumb.jpg.27d79449d34a6f0b40467012fb932cba.jpg

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That all seems to check out then....

I wonder if the mag info has anyway to check and verify the impulse operation as it does run until the impulse cuts out at higher RPM?

See item 8. A broken Snubber ring will advance the timing of the impulse.

Page%2028.jpg

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James, it looked like that snubber ring is a component of the E4A mag coupling, not the F series. 

I took the mag off and put it on the bench, I don't believe there's any problem with the impulse coupling. I hooked up all the plugs to a spark jig and ran it at different RPMs and there is a spot at low rpm where there is intermittent spark. Do you think this could be from a weak magnet?  I built a magnet charger to do this and it's not all that considerably powerful. Although I went from a magnet that could not hold itself up sideways on the toolbox to one than can I would guess it's strength is 5 lbs or less. 

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Well I hooked a welder up to my magnet charger and got that magnet charged pretty good. That magneto has a real nice hot spark that will draw out two about 5/8". 

Put it back together today and I'm back where I was before with no fire at all.  Spark plugs are sparking nice and hot, timing is the same as before.  Driving me crazy!  I'm going to see if I can get a guy I know to come look at it, see if he notices anything I'm not. 

I'll let you know if I make any headway.

 

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