Magneto clearance

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Model T Ford Forum: Forum 2005: Magneto clearance
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Eddie on Wednesday, July 11, 2007 - 11:04 pm:

How much clearance do you need from the coils to the magnets? the mains are rebabbited, the crank turned so I have little or no end play at the crank. The minimum clearance I get is .016" with the max at .023" the minimum is near the top of the mag.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob on Wednesday, July 11, 2007 - 11:39 pm:

I was told back in the early 60's the min should be; the thickness of a thin dime whitch is 18-20 thousants.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, July 12, 2007 - 09:35 am:

Thin dimes are hard to find now. New dimes are about .054 and way to much for a working Mag. I always go .030 + or - .002 all around and turn the crank 90 degrees and measure again and do that again and again to check all the cardinal points and insure the crankshaft end piece is not bent.

Here is what happens when you have .032 end play in the crankshaft, but the real problem was the screw backing out, even though it was wired with soft copper wire.

1


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Thursday, July 12, 2007 - 11:44 am:

Dave
Ford specs for the gap was not less than .025 and not more than .040.
When everything is newly rebuilt I like to see the gap set at .025-.030 with the higher number at the bottom of the engine where the field ring vibrates.
Ron Patterson


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, July 12, 2007 - 03:03 pm:

Interestinly, the contact occurred at the bottom area. I had never heard about the vibration problem, but did hear that was the critical area and should be checked very carefully.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James R. Patrick on Thursday, July 12, 2007 - 03:35 pm:

Isn't the gap at the bottom wider than the gap at the top to compensate for the wieght of the transmission and the resulting sag factor? Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Thursday, July 12, 2007 - 04:02 pm:

James A.
Trust me the unsupported bottom section of the field ring vibrates because of the magnetic coupling and can acually cause cracks in the casting around the lower mounting holes.
James R.
I don't beleive so. Remember the fourth main bearing in the Model T engine?
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Thursday, July 12, 2007 - 04:11 pm:

Ron, Is that total clearance or running fit? Ha, Thanks for your support, your a regular forth main!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Thursday, July 12, 2007 - 04:49 pm:

Glen
My wife says the same thing.
Ron Patterson


Top of pagePrevious messageNext messageBottom of page Link to this message  By James R. Patrick on Friday, July 13, 2007 - 07:17 am:

Thanks Ron.

Yes, I do know the fourth main bearing supports the weight of the transmission, but if it is babbited it can and does wear over time, which causes the magnets to move closer to the coils on the bottom. Plus, there is a little play in the four, fourth bearing bolt holes that, if not set properly, will not support the weight as it should, thus, the sag factor.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By James R. Patrick on Friday, July 13, 2007 - 08:04 am:

I meant to ask. What is the best way to properly set the rearmost fourth main bearing so that it supports the transmision properly, thus removing the stress this weigh poses on the third main? When the engine is sitting horizontally on the engine stand with the full weight of the transmission on the third main and you are ready to install the fourth bearing, with the hogshead installed, one cannot see the small gap between the bottom coils and the magnets to make sure the gap is properly maintained. I have always done it by feel and while I have been successful so far in not doing it wrong, I have always been very uncomfortable with doing it this way. Is there a better, more reliable method for doing this? It is such a close gap between rapidly revolving parts, that, a mistake here could destroy your engine. Thank you. Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By R.V. Anderson on Friday, July 13, 2007 - 10:31 pm:

Turn the engine, mounted on an engine stand, on its nose so that the 4th main is on top of the whole works. This is also the proper position for setting the magneto air gap. Make your adjustments to the 4th main and then bolt it in place. Now, the bolt to hole clearance is such that the cap can do a considerable amount of slipping even after a good torquing is applied to the bolts, so many of us drill and pin the cap to the pan in order to keep it rigidly in place before merely securing it with the bolts. Others of us use a good, hi-strength epoxy such as J-B Weld, reasoning that it can be removed later on with heat, and leaves a good surface for the next guy to install a new cap. Remember: "The tougher you make it for the next guy, the greater the chance that the next guy will be YOU."


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