A member of the 351C Rocks group on yahoo posted this about cam bearings. It sounds valid. I am wondering what others, especially Tim Meyer thinks about it.

"The problem with rebuilt Clevelands and oil pressure
is this; when replacing cam bearings, the typical
technique is to install the cam bearings, and then to
take an old camshaft and raise a edge on the front cam
journal and use it to scrape the front bearing until
the cam no longer binds on the front bearing. But this
can leave an excessive clearance on the underside of
the front journal of the cam - the worst possible
place for excessive clearance. This is the first turn
that the oil takes on its way from the oil pump. What
you have is a massive oil leak in the front of your
engine at the very beginning of the oil passages.

If I am recalling correctly, the way the factory bored
the holes for the cam bearings was to drill the front
hole, then gun drill the rest of the holes from the
rear. And the block was upside down, so gravity tended
to pull the drill down (toward the top of the upside
down block). They installed oversize bearings in the
middle three cam bearing positions and align bored
them to get them straight."

His proposal is to use oversize cam bearings and line bore to the correct size.

 

Yes I have also heard that the cam bearings are bored later. I have installed a large number of cam bearings in a 335 series block. I have never had to scrap the bearings to prevent the cam from binding. Besides, installing restrictors or drilling the cam bearing like we do would should counter the issue.

As I have discribed on our web site of the 400 engine project, I feel there is to much oil being lost to the front main bearing, that is why we now block off the main oil line, and open up the other feed hole to the main.

In the article we restricted the main line on the #1, but now we have blocked it off completely. We are doing this modification to all our racing engines at this point.

In my opinion, an engine oiling system is a system of leaks, controling the leaks help keep the amount & pressure in the proper locations.

 

Tim,

How do you drill the cam bearings?

Do you start with oversize bearings?

 

I drill a 3/32" hole about 90 degree from the original hole. #1 cam bearing I turn it alitlle as to block off some of the oil holes. There are 2 up front.

I use just a stock cam bearing.

 

While you are in there...how much more effort & dollars would it be to put roller cam bearings in?

 

I have 1 set of roller cam bearing on the shelf.

We have never seen a need for them yet.

Usually the block requires boring the cam bearing housing out.

We have stroker 302's in the circle track application. They use aftermarket blocks so they will be bored to 4.125" and we then have 360 cubes. These engines are making almost 700 HP. All we use in them are hard cam bearing that are coated.

 

so starndard bearings are good for roller?, what about push rods, are hydraulic ones good too?

 

Im planning to go roller to but why aint there double profile cams (int and ext diff duration)? 400 likes them, aint a single profile cam worse?

 

The off-the-shelf rollers are all single profile cams. To get a dual profile cam you need to go to a custom roller. The cam in my 434 is a custom dual profile roller.

 

If I am installing a cam in a new rebuild or a new cam in an older build, how much binding of the cam is acceptable. Should it turn free, or is some amount of effort OK.

It seems to me that the reason you need to restrict the oil feed to #1 cam bearing is because of a slight misalignment between the cam bearing bores, and disproportionate wear on the front bearing as a result. So, a newly rebuilt 335 series motor has good oil pressure, but in a short period the #1 cam bearing clearance increases and the oil pressure drops.

Restricting the flow to #1, cam bearing does prevent the oil pressure from dropping too much, but at low RPM when the oil pump is not putting out much volume of oil, the oil pressure will be low.

It has been stated that the oiling system on the 335 motors is just like many other motors, but other motors do not seem to share this problem. I believe that this is due to the misalignment of the cam bores in 335 motors. This may be better in some blocks, and worse in others.

I think that we need to quantify the misalignment, so good and bad blocks can be identified, and bad alignment corrected.

 

Just installed a set of cam bearings in a 351C today. Could have thrown the cam in from across the room, fit so nice.

 

Don't you run into some motors, where the cam fits tight even though the bearings are in spec?

 

are bearing spacers available to run a cleveland 2.75 crank in the 400?

 

Dan, yes there are times we have engines that the cam is tight, if I can turn the cam with the cam gear on using my hands, that is fine. other wise we scrape the bearing to fit it.

They do make a spacer kit for the 351W, and since the 400 & 351W use the same bearing, the same kit should fit in the 400.

I have used them a couple of times in the 351W's

 

What does the spacer kit do?