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Spitfire Camshaft Bearings - Current Part Quality Issues? Long Post

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Greetings all:

 

I tried to search for my cam bearing problem but came up empty.

 

My Spit6 has a 2.5L engine. Back in the mid '90s my engine suffered an oil starvation issue at one of the cam journals and damaged the bore. I had the block line bored and installed early Spit cam bearings (lined up the oil holes and pressed them in, cam slid right in, correct clearance,...). I recently pulled and dismantled the engine for some maintainance and thought I would replace the cam bearings while replacing the cam shaft. It appears that the only cam bearings available in the USA currently are Country brand, made in India. When I install the bearings (now much more difficult to press in) the cam shaft will not install. Some quick measurements lead me to believe that the bearing shell on the new bearings is 0.001 thicker and the OD is 0.002 to 0.003 larger.

 

I was told by someone in the Triumph business to have the bearings line honed after installing into the block - that just seems wrong - to remove the soft bearing plating on the ID of the new bearings. Instead I bought a small diameter bore gage, measured a new bearing in the block (0.0045 too small), and removed the new bearing. I machined an aluminum bar so that the bearing would fit over it, bonded the bearing to the mandrel and removed stock on the OD of the bearing. Now with the modified bearing in the block, the clearance to the camshaft is good but there is not enough interferance for the cam bearing to remain pressed in place in the block.

 

My old cam bearings have a noticeable wear on the bottom qtr of the circumference. I could reuse my old cam bearings. I could drill new oil galley holes in the old cam bearings so that the worn area would face up, but then the bearing seam would be face down in the high load area. I dont't like this idea. I have been monkeeing around with these cam barings for the last 4 Saturdays!

 

Anyone else aware of Spit cam bearing issues? Solutions? I can't be the only one with this issue. THanks for reading this far.

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I made my own line boreing tool for my milling machine.

Also the bearings are custom made to the drilled

diametre of the holes in the block.

Material is CuSn12 bought as a thick diametre tube

in 51mm outside diametre.

 

Looks nice after fitment!

 

gallery_1431_55_16360.jpg

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I think you need to find some Vandervell bearings which come up every now and again. I would call Chic Doig sports cars in the UK as he has a load of bits and bobs that are of use.

 

Chris.

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I recently installed the County cam bearings in a 6 cylinder block. I did have LOTS of issues, but these were related to the monkeys machining the block rather than the bearings. Once the block(s!) were correctly machined the bearings fitted fine

 

Nick

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Yes, the proper guidance of the cam is directly related

to the proper line drilling of the block.

If its to big the bearings pop out, if too small the cam sticks.

 

If somebody did wrong my opinion is you have to cheat.

 

As the stock spitfire bearings have a steel layer and are

plated with a thin layer of tin the solutions are limited.

As these bearings are not round when on the table

one has problems to machine them when not in the block

and after fitment in the block final line drilling is expensive

and might destroy the bearing.

 

With a bearing totally in one material you are free

to find a proper clearance in any bore if its made

in one step inside/outside diametre with a lathe.

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Thanks for the replies.

 

Nick:

How long ago did you buy the Country bearings? I received a response to a similar question on a US based list and the individual bought his Country cam bearings 3/4 year ago (and had no issues).

 

Triumph-V8:

Do you have any pictures of the line boring tool you made or of it in use that you would care to share? Were you able to line bore end to end in one pass or did you set up and bore from each end of the block? I also have a mill but it does not have quite enough travel to bore on a single pass (plus I lack the creativity in imagining how I would fab a boring tool and hold concentricity to the axis of the camshaft).

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This is the boring tool:

 

gallery_1431_55_15589.jpg

 

On the right side it will be fixed to the head of the machine.

As you can see there are cross drilled holes to accept

the tungsten steel round cutter.

From the rear you find a thread to accept a screw that

fits into that hole to push the cutter forward/backward.

 

Rectangular to that is a threaded hole to accept the screw

to hold the cutter in position.

 

The boring bar is hold in postion on the right by the machine head

and on the left it needs a bearing that is carefully setup and mounted

to the engine block to have the boring bar in the middle of the bores.

 

Each cam bearing is drilled in steps and controlled from time to time.

After one is finally bored the cutter comes into the next hole in the bar

and the fun starts again.

 

This is the position of the block on the milling machine

machine head is turned 90 degrees.

 

gallery_1431_55_31795.jpg

 

For centering the boring bar it is heplfull to make adapters

smooth slide fit into the cam bearings and boring bar

and than let the bar slide smooth into position,

move engine block towards the machine head into postion

that the front of bar slides into the machine head

and at last mount the rear guide plate for the bar to the block.

Than remove the adapters bring the cutter into position and start!

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I was surfing to harvest expansion tank / plumbing images when I came across my own thread from years ago.  I figured I would close the loop as to what the problem was, how I found it and how I solved the problem.   The Country bearings were not the issue.

The block had been line bored for the Spit cam bearings.  The block had been lined bored very poorly. the inner most bores were 0.010 undersize.  It appears that the machine shop simply honed the cam bearings to suit.  The engine never had good oil pressure.  The only consolation is that the "reputable" machine shop went out of business in 2010.

My bore gauge only reached in to the second journal so I machined a stub of a shaft in 0.002 inch steps progressively undersize and used that as a go/no go gauge.  I studied Truimph-V8's excellent posting above, I made concept sketches but I was too scared to try to do my own line boring - in part because my mill has a table that is only 36 inches across.  To get adequate travel, I would need to bore from both ends of the block - this just seemed to be an accident waiting to happen.   And I am not a machinist - just someone who plays around with the big tools. 

I resolved to modify the cam bearing shells.  I made a mandrel to fit the ID of the bearing shells in their free state with a very light press fit.  I superglued (cynoacrylate adhesive (sp)) the shell to the mandrel and then used a toolpost grinder to remove stock from the OD of the shell.  Each shell was ground as needed to achieve 0.001 to 0.002 greater press fit as would a stock bearing in a properly sized journal.  The bearings were installed and then I took a junk cam and turned the first journal down (from memory) about 0.005, the second journal 0.004, ...   I cut a groove perpendicular across each journal.  My junk cam was now a stepped reamer.  Since the outer journals were correct to size and the 2nd journal not too much smaller my cam was entering the 3rd journal before it began its first light cut as I rotated the cam.  As the cam was inserted to the next journal the process began all over, but now light cuts on 2 journals.  I inserted the cam from both ends of the block.  Lots of cam rotation will the slightest of (manual) feeding in of the cam.  I took a 2nd junk cam (I have a habit of hoarding junk parts) and cut the perpendicular groove across the journal but leaving the journal dia as is.  This cam did more burnishing of teh bearing surface than material removal.   The end result is that only a few thou were removed from the bearing surfaces.  The newcam installed in the block required a bit more force to rotate than similar cams in other 6 cyl engines.   After 10,000 miles of use, oil pressure has never been better.

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