Camshaft clearance

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Model T Ford Forum: Forum 2015: Camshaft clearance
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Friday, June 05, 2015 - 07:15 am:

I have the timing cover off of my 26 to replace the timing gear and I noticed that the end of the camshaft is able to move up and down, with the cam retaining bolts in place. I have not put a dial indicator on it yet to get a measurement, but it seems like a maybe 15 thousandths. What would be considered acceptable, given that the bearings themselves are a slip-fit into the block? This is a recently rebuilt motor, running a Stipe 280 in new bearings, with about 8,000 miles on it. I'm replacing the timing gear because a newly installed alternator damaged the aluminum gear and my oil was showing non-ferrous metal dust. The new gear is a nos iron gear and the alternator is gong to stay on the shelf.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Bender Tulsa Oklahoma on Friday, June 05, 2015 - 07:46 am:

The cam bearing is a slip fit into the bore almost a slight press. You have to much clearance between the bearing shell or the cam bearing to camshaft fit is wrong, or a combination of both. Should be .002" bearing clearance and end play.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Jablonski on Friday, June 05, 2015 - 08:36 am:

Could the metal debris you described worked its way into the cam bearing ? I would install a new/rebab front cam bearing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Friday, June 05, 2015 - 09:37 am:

That metal debris could have reeked all sorts of havoc on my nice new babbit. I will pull the cam out and inspect the cam bearings. So, I take it that there should be no noticeable movement when one moves the cam shaft? I found this when I went to check the gear backlash last night. I had put the new timing gear on and then "wiggled" it with two brass bars to see how the gear mesh was.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Friday, June 05, 2015 - 11:38 am:

For what it is worth, Dave, the likely reason the aluminum gear got torn up is because the alternator gear was set to the wrong pitch diameter relative to the timing gear. Few folks know or take the effort to adjust the shims on the generator bracket to properly set the pitch diameter when changing devices.
Since I rebuild generators and have no trouble with reliability, I personally would never install an alternator in a "T", but in this case it's a moot point and I doubt that your alternator was the root cause of the timing gear failure. Shelving it may not actually be necessary.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Friday, June 05, 2015 - 04:17 pm:

Scott. Can you expand on the process? I had messed with removing and adding gaskets many times before throwing in the towel and going back to the generator. I tried double gaskets, custom gaskets, etc, trying to get to a "decent" backlash in the gears... Although, all through trial and error. Any guidance would be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting, Clare, Iowa on Friday, June 05, 2015 - 06:24 pm:

You add a shim be hind the casting, that holds the generator, part 3017.

Its a "L" shaped gasket.

Herm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, June 08, 2015 - 11:51 am:

Dave, Herm is right, of course. Reading your latest post makes me think that you already tried that? If you could not get some minimal backlash by doing what Herm said, then the gear on the alternator was bad.

Now, just for completeness, I'll reiterate: the shimming takes place between the block and the casting that holds the generator, like Herm mentioned above...NOT the gasket between the generator and the casting...adjusting that would have no influence at all...

One final thing...I ran into a case with a friend who was trying to install an alternator on a '13 block and the alternator housing actually touched the block at the back end, and would not allow the alternator to seat squarely on it's gasket. In this case, it was fairly detectable and obvious, but perhaps you have the same thing but wasn't so obvious?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Monday, June 08, 2015 - 01:16 pm:

You can't set the pitch diameter. Pitch diameter is a gear measurement and will remain constant for any given gear. (It's the number of teeth, divided by the pitch) What you're setting is the center spacing between the cam gear & crank gear. Since that's not an easy thing to measure, you instead check for the proper backlash, or clearance, between mating gear teeth. Given 2 gears in good condition, the center spacing can be assumed correct if the proper backlash achieved.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Monday, June 08, 2015 - 02:11 pm:

Jerry. Point taken, and you are right...I used wrong terminology. I should have used "backlash" instead. Terminology aside, the advice to add or subtract shims on the generator bracket still stands, though. As an aside, it isn't the cam/crank gear spacing that appeared to be the trouble per original complaint.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Monday, June 08, 2015 - 02:18 pm:

Scott,

Yes, shimming is still important. Sorry for being a stickler.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Scott Conger on Tuesday, June 09, 2015 - 06:00 am:

Jerry...no need for any apology. I used improper terminology that may have misled someone in the future for reasons that I can't fathom today. I'm glad that you made the point.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Tuesday, June 09, 2015 - 06:53 am:

Guys. It seems everybody missed the point of my original question. The fact that the camshaft itself moves up and down in its fixed location is making it mute to check the amount of backlash within the 3 gears.

I did put a dial indicator out at the end of the camshaft, where the timer nut would be. It can be pulled up 9 thousandths. I realize that this is a long distance out from the front cam bearing and thus magnifies any actual bearing/housing play. My question is: what would be considered acceptable movement?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, June 09, 2015 - 07:23 am:

Since the cam shaft is held by three bearings evenly spaced along the length, I wouldn't count on much magnifying of the play due to the rather limited distance from the front bearing. The first answer from Mike Bender tells everything - you have a problem with the front bearing and it's best to take out the camshaft assembly to evaluate exactly what's wrong.

Many times original camshafts and original bearings are in good shape regarding the radial play, I've been able to reuse original bearings in my two engines. If the axial play is too much, it's easy to make a thrust bearing between the cam shaft nut and the timing cover with a couple of steel washers and a nylon/teflon washer. Chaffin's sells a ready made kit.

Many have had problems with the repro cam bearings - they're often oval and has to be bent back to round with some type of tooling. I have a couple of repro bearings of unknown manufacture I can't use - they're oversize, but I don't know about any camshafts that are oversized in the bearing areas?

So my advice is to try finding a couple of good original bearings and a washer set for the axial play - if needed. Then check the backlash for all gears :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem - SE Michigan on Tuesday, June 09, 2015 - 10:44 am:

Dave,

"Guys. It seems everybody missed the point of my original question."

Your question was answered by the first response, given by Mike Bender.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Tuesday, June 09, 2015 - 04:55 pm:

Roger that.


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