H4 Magneto Problem

[Bookman]

I inquired earlier about a mounting flange for the H4 magneto on my 1946 International A tractor. I found one at a local auto electric shop. Their long time magneto guy rebuilt the magneto since he found some internal problems and he bench tested it (I watched him). Firing fine on the bench.

Took it home and installed it on my tractor just as I had taken it off. However it was missing and not firing on all cylinders. #3 cylinder missing. I got out the manual and noticed that it was installed not like the manual said. #1 cylinder was wired into the magnet on the connection next to the engine, so one connection off all the way around. I redid the connections as manual said. However, the engine then backfired badly and would not start.

So I started over and tried to retime the mag to the engine. I did as the manual said and got number 1 cylinder to the top of dead center. I checked for the D.C. mark on the flywheel. Now there is a paint mark there but I could not find for sure the D.C mark as described in the book.....and I looked hard. I then removed the distributor cap and turned the magneto coupling until the metal strip on the distributor rotary pointed toward the No.1 terminal on the distributor cap per the manual. i felt pretty good since impulse would trip just as I reached the top of cylinder #1 as the manual said.

Put it back together and cranked over the engine. It back fired and would not start.

I put the wires back as I originally took them off with #1 next to the engine on top instead of outside top. Tractor started but would not fire on #3. Color me frustrated. The mag does rotate clockwise.

Now it has been converted by a previous owner to 12 volt with an alternator. I have had it almost twenty years that way. And it was running fine until I had the mounting flange replaced, and it did test out on the bench. Any recommendations??

 

[Janicholson]

If his is off base do not take it personally. The firing order on the side of the engine says 1342. It is correct,
but the front of the tractor is #1. if wired the other way. it will run on 2 cylinders. Jim

 

[Bookman]

The wires are connected in the right order with the front of the tractor cylinder being #1. I just wonder if the fellow who did the mag did something wrong internally It just backfired when connected as the manual says...1,3,4,2 with the 1 starting on the outside top. Then it runs but #3 does not fire when wired in the same sequence but beginning with the inside top as #1, and then outside top as #3 and so forth. Thanks for the thoughts though.

 

[Janicholson]

Try changing the plug from #3 to #4 and see if the misfire follows the plug. If so it may be fouled or bad. If not check the compression on #3. Jim

 

[Bookman]

I will give it a try but the tractor was working before the magneto was rebuilt.

 

[John M]

Couple of things come to mind. When it was rebuilt, he did not get the gear inside in the right spot, and/or you have it timed TDC on exhaust stroke, which I think it may be. As far as the one plug not firing, look at the cap. There may be a crack causing #3 to not fire.

 

[Bookman]

I will double check but I am pretty sure I have the timing on the #1 cylinder right. The air should come out of the spark plug hole as the piston comes up. I use a piece of wire to check and make sure the piston reaches it top dead center. When I did this yesterday, the impulse coupling tripped, which I think is what is supposed to happen. I did not see any cracks on the distributor cap but I will double check it again. I will switch wire three and four and see if it still misses on that cylinder. Kind of running out of ideas. Now I suppose a spark plug wire broke in taking them on and off. If I cannot figure it out this morning, my next step is to take the mag, along with the spark plug wires and the spark plugs back to the auto electric shop and have them check it all out. I am not an experienced mechanic so I could be missing something, but I do know I had a running tractor before I took the mag in. It was rebuilt and now I do not have a running tractor. Thanks

 

[gene bender]

Air also comes out on exhaust stroke when piston comes up are the valves both shut?

 

[teddy52food]

You have a cap or wire problem. If it is firing & running on 3 cylinders, the mag is working as it should.

 

[Dave41A]

What you describe seems to be two separate problems. The first is that the #1 cylinder wire is not where it should be. This implies that the magneto is installed 180 degrees out. The second is that cylinder #3 is not firing at all.

You seem to be doing all the right things regarding the magneto being 180 degrees out. I don't think I can help you there.

However, for cylinder #3, I would check the spark plug and wire. I recently converted my 41H from coil to magneto and learned that magnetos need copper-core wires and non-resistor spark plugs when it wouldn't start. It is possible you have an odd-duck wire in there. See if the problem migrates with the wire and/or plug. I am running autolite 3116's in mine.

Also, as the others noted, also check the cap and rotor. I am not sure if your re-build included a new rotor and cap. If it did, then one thing I have noticed is that the new ones are slightly different dimensions than the old. For example, on my 41A, I re-built the magneto and put a new rotor on it. However, the new rotor was significantly taller than the 78-year-old original, and as a result, the metal contact on the rotor was actually striking the inside of the cap as the engine ran--if it ran at all. I ended up re-installing the original rotor (with "IHC" logo and small nut holding the metal contact in place)and it runs fine.

To illustrate how sensitive they can be, I have attached a picture of two aftermarket rotors (both without IHC logo). My "H" runs *only* with the lower profile rotor (on the left), while the one on the right strikes the inside of the cap--in this case the tractor runs poorly if at all. Notice how the rim on the right is a little thicker, and the contact is just a touch higher.

If not installed already, and you still have the original rotor and cap, try re-installing those, and see what happens. In short, there is some slight difference between cylinder #3 and all the others, and it could be any of a number of things. Your cap/rotor combination may be one of them (or not at all).

 

[Bookman]

Thanks, I will try to bring everyone up-to-date here. I took the magneto off, along with the plugs, and wires, and took them all back to the auto shop. The magneto is firing fine. The wires are all good. One spark plug (#3) was fouled. The fellow at the shop sand blast them all. He showed me how to turn the rotor counter clockwise so the magnet fires at the #1 cylinder when its wire is connected at the top outside terminal. I went back home retimed the tractor to the mag (e.g. the #1 piston at top dead center). I put the mag on and start the tractor. It fired up but is still missing. I ran out of time today, but I going to check the firing against tomorrow to make sure each plug is getting electricity. Them I want to check the compression on each cylinder. What would be an acceptable compression for this tractor? Am I missing anything? I suppose I could have the timing off but it sure felt like #1 piston was clear to the top, and the rotor was pointed to fire at that point at the #1 cylinder when the wire was connected to the top outside connection. And it was at the top of the compression stroke with me feeling the air as it came out of the spark plug hole. Thanks for all the good advice and thoughts.

 

[Janicholson]

I f your tractor is gasoline only, 105 to 130 is good. If it is a distillate tractor and has a small gas tank for starting gasoline (or a hole where the tank used to be in front of the gas tank in the hood) around 90 to 110 is fine. Do it with all plugs out, throttle wide open, and do it with a fully charged battery. Crank it a uniform number of compression strokes (usually about 6 or 8 are required to get the pressure up to where it is stable. Jim

 

[Bookman]

Gene, Not sure what you mean. I thought air would not come out the spark plug hole on the exhaust stroke...unless the valves were close, which they should not be. Right? I did respond elsewhere as to progress to date. Thanks

 

[Bob]

(quoted from post at 20:43:13 06/18/19) I inquired earlier about a mounting flange for the H4 magneto on my 1946 International A tractor. I found one at a local auto electric shop. Their long time magneto guy rebuilt the magneto since he found some internal problems and he bench tested it (I watched him). Firing fine on the bench.

Took it home and installed it on my tractor just as I had taken it off. However it was missing and not firing on all cylinders. #3 cylinder missing. I got out the manual and noticed that it was installed not like the manual said. #1 cylinder was wired into the magnet on the connection next to the engine, so one connection off all the way around. I redid the connections as manual said. However, the engine then backfired badly and would not start.

So I started over and tried to retime the mag to the engine. I did as the manual said and got number 1 cylinder to the top of dead center. I checked for the D.C. mark on the flywheel. Now there is a paint mark there but I could not find for sure the D.C mark as described in the book.....and I looked hard. I then removed the distributor cap and turned the magneto coupling until the metal strip on the distributor rotary pointed toward the No.1 terminal on the distributor cap per the manual. i felt pretty good since impulse would trip just as I reached the top of cylinder #1 as the manual said.

Put it back together and cranked over the engine. It back fired and would not start.

I put the wires back as I originally took them off with #1 next to the engine on top instead of outside top. Tractor started but would not fire on #3. Color me frustrated. The mag does rotate clockwise.

Now it has been converted by a previous owner to 12 volt with an alternator. I have had it almost twenty years that way. And it was running fine until I had the mounting flange replaced, and it did test out on the bench. Any recommendations??

If the mag "fires" the wrong "nipple" at #1 TDC, either the governor/mag drive timing is "off" or the rotor drive gears aren't timed correctly.

It is even possible that the governor timing is "off" and someone previously made up for that by resetting the rotor timing, and your mag guy corrected that, so know it doesn't match the drive timing.

But, no matter, if you can get spark timing correct with the wires one nipple "off", there's no need to change anything else (unless you want everything as it left the factory).

I believe I replied to your previous post with a link to the factory mag manual, which explains rotor drive gear timing in detail.

Also, find the flywheel timing mark. It's there if you wire brush the area, and look closely.

As to the exact compression PSI, it's more important that the readings be consistent across all 4 cylinders, within a few PSI, if #3 is significantly lower than the others, you'll know there IS a problem with that cylinder.

 

[Dave41A]

It sounds like you have solved the magneto timing problem; e.g. getting #1 to fire when the rotor is pointing to the outside top plug wire. It seems like the miss on #3 is what remains. If so, the tractor should at least run on 3 cylinders, but not smoothly.

I know the wires and plugs are all good, but does the problem migrate with the plug and/or wire, or is it always #3? Does the problem occur only at idle, or at all engine speeds? Does a little choke affect anything? If it is always #3, then it must be something mechanical with that cylinder. Could be spark plug not sealing, valves not closing, excessive blow-by of the rings, or even a vacuum leak in the manifold gasket resulting in a too-lean-to-fire mix for that cylinder. If choke fixes it, then it is a vacuum leak most likely. A squirt of clean engine oil in the "pocket" around the spark plug can help detect a spark plug leak (watch for bubbles), which is where I would start as the other components were not changed at all unless you had additional work done. The oil can also help prevent the plug from sucking air on intake, which will also make that cylinder too lean to fire. A little oil into the spark plug hole itself(e.g. on top of the piston with the plug removed) can help detect worn rings in a similar way if the plug leak test comes back negative.

 

[Dave41A]

I should have added "spark plug gap" to the list. A plugs can spark outside the cylinder, but not inside, where the pressure is different. But this problem would migrate with the spark plug if installed in a different cylinder.

 

[Grandpa's Fords]

Recently after starting up 16 yr sitting H, miss on no#3 after checking ign system found no issues. Popped valve cover off to find rocker loose enough that it was off the push rod. No damage visible reset and checked/set remaining valve clearance. Smooth as silk. I guess I got lucky, I've heard it happens.
RE: Dave 41's rotor observation, the taller rotor chewed the cap button off. The taller rotor was in a box of spare parts that the fil had for it. and the cap was IH NOS. Replaced with Echlin rotor and cap all good.
Just something else you could check.

 

[Grandpa's Fords]

Should have mentioned compression check showed very low compression on #3 before I pulled the valve cover off. I was hoping to find what I found when I did. Intake valve closed.
I have experienced a loose set roker coming off a push rod in an older engine before after a backfire or misfire. It's possible my 72 year old H never had a valve cover off. Most of the valves were slightly loose.

 

[Bookman]

Thanks, I had some pretty good backfires so I probably should pull the valve cover and take a look. I hate it when I create more problems trying to solve a
problem. I appreciate the good advice. I hope to get to tractor this afternoon.

 

[Bookman]

Thanks for the good advice. I am going to try to get back to the tractor this afternoon and see what I can trace down. My order of testing is 1) check the sparks; 2) do your spark plug leak test; 3) do dry and wet compression test; and 4) take off the valve cover and see if I can identify a problem there. Of course, depending on the results I may not need to do all three. Thanks for good advice.

 

[Bookman]

Thanks much. I hope to get back to the tractor this afternoon. I post some responses to other suggestions.

 

[Dave41A]

You're welcome. I think Grandpa may be on to something with the valve suggestion. If the rocker arms under the valve cover are set too tight, then one or the other of the valves may be held open a little, possibly resulting in a non-firing cylinder.

But hopefully cleaning & gapping the plug does the trick. 0.025" is the proper gap if I remember correctly, which is tighter/closer than many modern plugs. Wider than this it may appear to spark outside of the cylinder, but it won't spark under pressure when installed.

You could also have a leaky valve guide or some other situation with that cylinder which introduced some oil in there and caused it to foul. Your carb may also be set a touch rich, which would foul all the plugs, but you just noticed it on #3 first. Look for black soot on the plugs.

 

[Bookman]

I will try to bring everybody up to date as to June 21. I timed the mag to tractor or vice versa and put the wiring back on. Two and three cylinders fire; One and four do not. I changed the spark plugs that were firing to the cylinders that were not. Still One and four do not fire. I thought maybe rotor upside down. I turned it 180 degrees and same result. I then compression tested the tractor with the following results:


One Two Three Four

Dry 30 32 50 40

Wet 32 45 50 40



I would say low compression but still four is not firing with higher compression than two with lower compression when dry. I showed it to a tractor mechanic (a real one ..unlike me) and he thought they all should be firing at that compression. I took the valve cover off and did not see anything obvious (as in broken etc.) The tractor mechanic is coming out Saturday afternoon after he gets off work at the mechanic shop where he works. Maybe with an experienced eye he will find what is wrong (and maybe it will be something obvious). Thanks for all the advice folks.

 

[Dave41A]

OK, so before 1,2,and 4 were firing, and now only 2 and 3 are firing? Those compressions indicate a well-worn engine, but if the tractor was running before, it should run again. It is odd that two cylinders would just drop out like that. By chance are wires 1 and 4 reversed? It is also possible the wires are not firmly on the plugs or installed well in the magneto. The good news is that this is definitely a spark problem, not a mechanical one.

 

[rustred]

I took a quick look here your problem. . you say u checked compression, but seeing those low numbers wonder if the gauge is accurate. 30-40 psi is definitely too low. should have at least 75 psi and higher for it to run. plus you also said it ran before. didnt see anywhere that you checked the valve lash , very important. .017 is the spec. the firing order is 1342 so check the two valves for each cyl. in that order at TDC on COMPRESSION. notice you don't say anything about having it on compression stroke, as that throws everything off 180 degree's. if the valves are indeed tight there is your low readings or faulty guage. a valve setting is classed as a major tune up with everything else including the carb job. plus every engine has there own number one plug wire position. on these tractors #1 position is about the 2 oclock position with wires in the clockwise position 1342. viewing from the back of tractor. left is left right is right. many have no clue as o left or right on an engine. plus when doing this compression test you need to run it over 5 compression puff's per cyl. you will get most of the reading on the second puff and then the third puff pretty well is max compression and the last two you gain very little like maybe ten lbs . plus so you know the diesel engines have a counter clockwise firing order. meaning the wires are placed counter clock wise on the cap. also you said you had the mag worked on so just a thought as to if the correct parts were used.

 

[rustred]

you said you turned rotor 180 degree's. you cant just turn it 180 degree's cause it has slots and only fits one way. plus mechanic is partly right saying it should fire at that compression... yes should fire don't mean engine will run. plus if # 2 and 3 are firing and running on 2 cyl's then could swap wires 1 and 4 and should be good... but that puts it at counterclock wise rotation. so that makes no sense. I think we are missing some info here. the firing order is 1324, so remove the plugs and hook the 4 wires to them and have each one grounded with a wire then turn the engine over slowly with hand crank and watch if all plugs fire in the order of 1342. if so then you need to time accordingly starting with #1 cyl. at TDC on compression, to where the rotor is pointing. don't mean you will have factory position. that's another story.

 

[Bookman]

Okay folks, here is the story. The tractor mechanic was here. Took awhile to figure it out but he got it. The magneto was set up to run as a distributor so the coil was disconnected. I took it into the auto electric shop to get the mounting flange replaced. The mag guy opened it up and saw the coil wire disconnected, so he replaced the coil. He showed me the old coil with the lose wire unconnected. I (in my ignorance) asked him why was it working fine on the tractor. He said he did not know. Well with the new internal coil reconnected, essentially there were two coils operating. In my view, when I showed him a picture of it on the tractor, he should have known. And when I told him there was no wire running of the coil to the center of the distributor cap he should have known. But, he fixed as a magneto (and no doubt did a fine job), and I did not know any better. He probably figures I should have told him, but I know not what I know not. Tractor runs fine now. Yep compression is low and it will probably get an overhaul this fall when I am done mowing with it. Thanks for all the help. As usual hard to diagnose things from a distant.

 

[rustred]

yes as I said missing info. but still confused about this coil thing. so your saying the mag was running an external coil on it? now its running on its own internal coil? better recheck that compression as im sure its higher than you say. 30 psi don't cut it. the thing is, cant diagnose with out complete and proper info.

 

[Bookman]

Thanks but read my response earlier today. Mag man repaired it as a mag but it had been modified to work as a distributor. Thanks