Strange timing on 8n (front mount dist.)

Somehow my distributor has a built-in "retarded" bias to it (static alignment gets me 1/2" from the hole instead of 1/4"). Have confirmed this by comparing against a "nominal" 1/4" distributor using a timing light (same point gap, same RPM).

And I can get the tractor to run quite well (no misses or coughs) if I "retard" my already retarded distributor all the way (timing screw 'up') and also close the point gap severely (to about .008, which I obviously would like to avoid as a permanent solution).

The tractor was overhauled at one point in the past; the head has been shaved significantly (the pistons will lift the head without a gasket), and I have very high compression (120 psi all 4 cylinders). The timing gear is a bolt-on type and is in alignment with the drive gear. Valves seem OK and seem to seat well; they're gapped a little loose (about .002 over specs).

I've heard that when the timing/drive gear marks are aligned you're at TDC. Anyone know if this is true? I marked TDC on my driveshaft pulley when I had the head off but when the gear marks are aligned my pulley TDC mark seems to exactly 90 degrees behind where I thought it should be. Is there any similar rule with respect to TDC and the drive gear key?

Finally..I did switch from a 6v system to 12v (with 12v coil). Could that cause any significant spark advance in and of itself?

Thanks in advance...

Advance not working: You Need to Remove the Points Mounting Plate. Points Out, condenser lead out of the way
note the timing adj screw position and remove screw.

Note the "LOOP" Position of the retaining Ring and remove the Ring.

The outerbearing & point plate assy will come off
the shaft.

Pull the shaft Assy and you should be able to see your problem.

Phil (NJ)

Prime candidate, as said, is the centrifugal advance assembly. This may be stuck, it may have something broken which is jamming it in a more reatrded position than it should be, and so forth. Pull it out of there and find out what it is.

If you marked TDC on your crank pulley when the head was off, then static timing for that cylinder (I presume it was #1) should be at TDC. You can check this with a timing light (if it will run) or an ohmmeter across the points (remove the coil to access the contact screw).

HTH

llater,

llamas

Checking the centrifugal Advance: "Using one hand to hold the Drive side", rotate the Rotor CCW (Counter Clock Wise) Left. It should move about 25 deg and you should feel Spring Tension. Release and it should spring back to the original Position, Check by trying to rotate CW (clock wise) right. It Should Not MOVE. If the assy is in the full CW position, the 1/4" spec will be correct unless it was pinned incorrectly at the factory.

Hope this Helps,

With higher compression comes faster burn of the fuel mixture in the cylinders. As such, you retard overall timing. With a lot of compression, you retard timing quite a bit. If you were to set the timing to the oem very low compressing settings, you'd ping if you were lucky, and more likely blow a hole right through a piston.

It's a valid technique to run valves loose to reduce overlap and alter valve timing. It keeps the fuel consumption down and shifts the power band. Not such a big deal on a stock cam, but very significant if running a "hot" cam. something I suspect you may well have.

So, for what it's worth, I suspect your engine is not stock, and is set up for its hot rodded conditions. Document the heck out of what you are doing, because you may well have to reverse everything you are doing or attempting to do. Try not to destroy the engine in the process.

What got me started on all this was a slipping #1 sleeve which is why I originally did the teardown. Plus I wanted to do a 12v convert. Everything inside (e.g. bearings, sleeves) looked pretty good & it was obvious there had been a rebuild at some point.

Before I tore it down it was hard to start but ran well when warmed up (except for the noisy sleeve). Unfortunately I neglected to first make note of things like timing settings, gap settings, plug wiring (could it have been staggered?), head gasket thickness, etc.

FYI I compared the timing of the old and new distributors at same RPM (1500 +/- ?), same point gap (.010) and same timing setting (middle). The new dist. was somewhere around 30 deg. BTDC; the old one was almost right on TDC. And if I run the retarded dist. at .008 gap & timing screw fully retarded, it runs well at RPM with only an occasional cough (one every minute or two). Timing at RPM looks like about 10 deg. ATDC.

So the only ideas I have at this point are (1) to tweak my distributor by extending the timing adj. slot to provide a little bit more retardation, or (2) perhaps double up on the head gasket to try and reduce the compression a little. Your thoughts appreciated...