Cam bearing keeper/screw in pin

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Model T Ford Forum: Forum 2013: Cam bearing keeper/screw in pin
Top of pagePrevious messageNext messageBottom of page Link to this message  By R. S. Cruickshank on Saturday, July 20, 2013 - 05:56 pm:

Just got back from a week touring in the beautiful Georgia mountains. I am pretty sure that the cam bearing keeper on the front bearing is not tight in the bearing hole and therefor I have the thrust issue and a noisy timing gear (new). Any suggestions on how to correct this? The bearing is good.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Saturday, July 20, 2013 - 06:21 pm:

If you don't mind a little work, you can fit the after market thrust kit that is used on re-ground cams inside the timing gear cover.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Saturday, July 20, 2013 - 06:32 pm:

Kerry, I have never used one of those kits, and I am sure they work fine, but what makes a reground cam different then a new one for operation?

Thanks Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Saturday, July 20, 2013 - 06:57 pm:

Are you talking about the bearing moving back and forth or the bearing wallowing in the bore? If its the bearing moving back and forth you could do as Kerry suggested or make a oversize bolt,or maybe use a piece of thin wall tubing and file a shim to fit. If its the bearing wallowing in the bore then Loctite is probably your answer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Saturday, July 20, 2013 - 07:13 pm:

Herm, if I'm understanding your question right, some re-ground cams have the thrust ground off the front lob, so the thrust kit is fitted to compensate, are you not familiar with this?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stephen D Heatherly on Saturday, July 20, 2013 - 07:37 pm:

Herm, If I am reading your question right you're asking why thrust washers are sometimes necessary? I'm sure that you know that the earlier cam bearings are longer and have a notch cut into them to clear the first tappet. The thrust surface is only on the lower part of the bearing. When the front exhaust lobe is up the (correct me if I use wrong terminology) base circle is relied upon to keep the cam from pitching forward. When a cam is re-ground this part is ground flush with the shaft. Now when the lobe is up the cam has nothing to keep it from shifting forward. That is why it is necessary to install the thrust washers. Of course, with a later cam 24-27 this is not a problem.

Stephen


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Saturday, July 20, 2013 - 07:41 pm:

No, I have never seen the rear lobe done anything to it, but grind just enough to true, and that should be done. then you fit the cam bearing to .002 thousandths end play.

Is that a fix for a messed up cam?

Herm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Saturday, July 20, 2013 - 07:50 pm:

No, Stephen, we don't have that problem, as we also grind the main bearings, and I pour our own cam bearings.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Sunday, July 21, 2013 - 05:36 pm:

Herm, When you regrind a cam you must remove material from the bottom of the lobe to restore lift. When you do this on an early cam you remove the lower thrust surface of the front lobe leaving only the toe as a thrust surface. when the toe rotates to the position where it is in line with the notch on the rear of the early bearing the cam can thrust forward into the notch. When the lobe strikes the side of the notch it causes a knock. Our thrust bearing kits prevent this from occurring. This is not a problem with the later cams as the front bearing has no notch.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Sunday, July 21, 2013 - 06:43 pm:

Glen, we always had the mains ground on all the cams, along with the front thrust, on the cam.

Not all cam lobs have to be ground that far, and if we had one, the cam grinder man , when he ground the mains, he would not grind all the way to the other end of the shaft.

He would leave a thrust collar on the rear of the bearing surface, about .015 thousandths wide, and I would bore the hole, set the bearing housing clearance, and then counter bore the rear of the bearing to fit the babbitt part of the thrust.

So, where the cast part of the bearing is thrusting on the cam lobe, when it gets to the notch, the babbitt its self is still a complete thrust.

I am sure your thrust kits work fine, and they sound good. But the time was only about 3 minutes to counter bore, so I did them this way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, July 21, 2013 - 08:49 pm:

The forward thrust on the cam is the No 1 exhaust lobe. If I read it correctly, you are grinding down the front journal also so you keep the thrust that that lobe on the cam provides on the engines that have the notched front cam bearing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Sunday, July 21, 2013 - 11:05 pm:

That will work Herm, but we do not grind the bearings as they are pretty small already. We just fit new bearings to the shaft as is and then use the thrust washers.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Sunday, July 21, 2013 - 11:50 pm:

Most of the cams I have Miced are standard to .003 to .008 thousandths difference on the same journal.

The only way I could fit something like that and have full contact as one would on a new one would be to cut the hole to the smallest diameter, say .005 thousandths under, and then hand scrape the rest to what ever is standard size, or to the largest Diameter. While that works, I would be burning up the customers money, or wasting my time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Monday, July 22, 2013 - 12:46 am:

The forward thrust on the cam is the No 1 exhaust lobe. If I read it correctly, you are grinding down the front journal also so you keep the thrust that that lobe on the cam provides on the engines that have the notched front cam bearing."END QUOTE

We are not grinding the mains just to get a thrust on the front main.

If they have average wear, in my opinion, they all need ground when a cam is built.

If part of the cam is std., and the rest of the cam is say the .005 under,and you fit the bearing hole to std, after the high spots wear off, you have a cam that has to much play.

So if you use .748, or .748-50 as a std. shaft, then you will end up with a bearing clearance of
from .005 new on the spot that is not worn, to .743-50.

So if you start out with .002 clearance, you will at all times have .743-50 thousandths clearance, either on the standard part of the shaft, or later on the standard part of the shaft.

The front thrust surface on a cam is the face where the bearing stops. The rear is and or was the cam lobe, or the raised part, not ground.

Grinding cam mains haven't made any problems for me, or I wouldn't do it.





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