MTFCA Forum

So I have this dummy delima. On the 9-24 front cam bearing; I have pulled 3 cams and the ends of the bearing seems to be broken. As you roll the cam; the lobe will actually drop in and that is a bad deal. I find it hard to believe that all 3 cams I pulled are the same way. Am I missing something? Thank you

Those are notches to clear the lifter head. The first lobe has a small edge to act as a back thrust, unless its been reground away. In which the cam lobe can hit & make ugly knocking noises. Consider front thrusting the cam with spacers between the cam nut & timing cover either way. Vendors sell a "kit" .

I love your Work Bench!..

Cap

As John has posted, the front bearing sets the float of the cam shaft, any more than 4 to 5 thou the cam can knock. Another thing that must be a firm slide fit is the bearing into the block. I like using the late cams on rebuilds as they have a wider front lobe so I use a earlier bearing by keeping the alignment hole in consideration, turn each end down in the lathe to be a float free fit.

I have been trying to track down a knock in my 27 for some time. It is quite elusive, I have checked all of the usual suspects-rods, mains, pistons, wrist pins, timing gears, etc. Using a stethoscope, the noise is most prominent at the timer cover. Could the front cam bearing be the culprit?

David, yes could easily be, although a cam knock is annoying, it dosen't really do any damage.

FundyTides wrote: ↑

Fri Jun 25, 2021 6:53 pm

I have been trying to track down a knock in my 27 for some time. It is quite elusive, I have checked all of the usual suspects-rods, mains, pistons, wrist pins, timing gears, etc. Using a stethoscope, the noise is most prominent at the timer cover. Could the front cam bearing be the culprit?

Oh yea!
I recently did a re rebuild on a motor with a bad knock. Turned out to be a "hot" reground cam with no thrust surface to the lobe. The hotter it got, the worse the knock. Cam vendor warns customers to front thrust it. Between cover & cam nut.
This kind of thing is less likely with a late (wide lobe) cam set up. But can still happen if a bearing half can move. & who knows if your motor still has the late cam?

My observation of the cam “knock” is it is “erratic”. Not there every turn. Now a centre main bearing knock will be throttle sensitive but there every turn at sort of mid speed and mid throttle. The cam knock will be erratic

Kerry wrote: ↑

Fri Jun 25, 2021 6:25 pm

As John has posted, the front bearing sets the float of the cam shaft, any more than 4 to 5 thou the cam can knock. Another thing that must be a firm slide fit is the bearing into the block. I like using the late cams on rebuilds as they have a wider front lobe so I use a earlier bearing by keeping the alignment hole in consideration, turn each end down in the lathe to be a float free fit.

Are you cutting down the earlier, notched front cam bearings(as shown)? To my calculations, narrowing the earlier bearing does not remove all of the notch.(stepped area) That still works ok with a partial notch? Have not tried this yet, but thought about it.

The most critical feature is that the 2 "broken" bearing halves fit together firmly. In my example the one side is , of course, held in position with the cam screw. The other halve was able to float loose. That floating 1/2 slides back & was hit by the cam lobe. There was wear evidence that that piece was moving as much as .10"

I Realize that front thrusting the cam would not have solved this knocking problem. It would have corrected the over ground cam heel. But it will also control the float of the cam/bearing.
I have been cam front thrusting all my recent rebuilds that dont run a bosch front plate. (Already built into the front plate)