22 replies to this topic

[pete l]

Hi all,
Building up my MPI engine. New cam bearings and a brand new MED camshaft.
Is it normal for it to be stiff to turn by hand with the sprocket on ? I've oiled it all up. The original cam spins freely enough. Will it free up as it runs in ? Or could it seize ?
Any ideas what I should do ?
Pete

[OzOAP]

If somethings tight,then it ain't right...when it comes to engines that is.

[Designer]

Hi,

 

Except F1 engines which are impossible to turn over until heated to the correct starting temperature.

 

Paddy

[OzOAP]

The last DFV I did turned over. Must have done something wrong.

[Cooperman]

The cam should turn freely by hand.

[Steve220]

Hi,

Except F1 engines which are impossible to turn over until heated to the correct starting temperature.

Paddy

Thats a myth, sadly. Tolerances are tight, but not so much it cant turn over.

[Spider]

Now you've fitted t and turned it, you'll have some witness marks on the bearings, Remove the cam and give the bearings a light scrape / shave on these high spots.I plain bar of 8 - 10 mm sq HSS I find ideal for doing these. Do not use any abrasives at all here. They will shed material off the paper or cloth and embed themselves in to the softer bearing material.

The Square HSS Bar Material you can get typically in 100 - 150 mm lengths from machine shop tooling suppliers, I wouldn't suggest anything too big as you want t to sit fairly 'flat' in the bearing, if it's too big, it will dig in. These are commonly used for making lathe cutting tools from and has a good edge, as supplied, in the square corners of the bar. Pass the bar through the bearing and gently scrape with it while keeping it parallel. If you still have an old bearing, even your old Mains or Big End, practice on them to get a feel for the technique.

If you are unsure of doing them yourself, tack it back to the machine shop. Most machine shops also ask for the cam you intend to run with when replacing the cam bearings so they can check and correct them as necessary.

[Designer]

 

Hi,

Except F1 engines which are impossible to turn over until heated to the correct starting temperature.

Paddy

Thats a myth, sadly. Tolerances are tight, but not so much it cant turn over.

 

 

Hi,

 

I stand corrected thank you.

I can't remember who it was but it was firmly stated on TV that that was the case.

When in fact they can be turned over cold but must never be started until all temperatures of all components and fluids have been raised to a set temperature.

 

Paddy

Edited by Designer, 06 August 2026 - 04:53 AM.

[pete l]

Now you've fitted t and turned it, you'll have some witness marks on the bearings, Remove the cam and give the bearings a light scrape / shave on these high spots.I plain bar of 8 - 10 mm sq HSS I find ideal for doing these. Do not use any abrasives at all here. They will shed material off the paper or cloth and embed themselves in to the softer bearing material.

The Square HSS Bar Material you can get typically in 100 - 150 mm lengths from machine shop tooling suppliers, I wouldn't suggest anything too big as you want t to sit fairly 'flat' in the bearing, if it's too big, it will dig in. These are commonly used for making lathe cutting tools from and has a good edge, as supplied, in the square corners of the bar. Pass the bar through the bearing and gently scrape with it while keeping it parallel. If you still have an old bearing, even your old Mains or Big End, practice on them to get a feel for the technique.

If you are unsure of doing them yourself, tack it back to the machine shop. Most machine shops also ask for the cam you intend to run with when replacing the cam bearings so they can check and correct them as necessary.

 

Oh dear :-( 

 

I did spin the cam and saw witness marques on the oil pump bearing, and I rubbed them down with different grades of paper, starting at 1500 grit, going up in stages to 7000 grit to get them nice and shiny again. 

The cam now spins freely and smoothly and the block is built up and on it's gearbox. BUT you've got me worried now. 

[Spider]

Oh dear :-( 

 

I did spin the cam and saw witness marques on the oil pump bearing, and I rubbed them down with different grades of paper, starting at 1500 grit, going up in stages to 7000 grit to get them nice and shiny again. 

The cam now spins freely and smoothly and the block is built up and on it's gearbox. BUT you've got me worried now.

 

Mmm,,, OK.

I don't know of any way to clean embedded material out of the white metal (and save the bearing). It will have Carborundum embedded in to it, which, as you've found, is a good abrasive.

What's also potentially worse, being such a fine grade, as some of that comes loose, the oil filter won't catch it.

I'd suggest replacing the bearing.
 

[pete l]

Not what I wanted to read, but knew was coming !

 

What would have happened had I left it tight ?

[pete l]

What cam bearings do people recommend ? I used standard ones from a french supplier. No name.
I'd like quality ones if possible.

[Spider]

What cam bearings do people recommend ? I used standard ones from a french supplier. No name.
I'd like quality ones if possible.

 

My favorites are ACL which in our local production were OEM.

[pete l]

Thanks, just ordered some and they were cheaper than the first ones I bought!

[GraemeC]

Cam bearings come intwo variations too - pre-sized or not.  I think ACL tend to be pre-sized though so you should be good (from memory, OEM Rover ones weren't and needed to be sized after inserting)