Milling cam box question

[pooldoctorstl]

The base circles on my race cams are smaller than stock and requiring shims over 5 mm. I read here (BEEK and Fiatfactory) that they have milled the boxes to use thinner shims. My machine shop is worried that cutting 2 mm off of each box will result in the need for a shorter belt. I am using Miller adjustable gears so I am not worried about cam timing, but do I need to worry about the belt? I think the tensioner has enough travel to compensate for the extra length. It is roughly 1/8" total.

Or, what is the max that I cam mill off of the boxes?

Advice please....

Thanks,
Jeff

[FiatMac]

The base circles on my race cams are smaller than stock and requiring shims over 5 mm. I read here (BEEK and Fiatfactory) that they have milled the boxes to use thinner shims. My machine shop is worried that cutting 2 mm off of each box will result in the need for a shorter belt. I am using Miller adjustable gears so I am not worried about cam timing, but do I need to worry about the belt? I think the tensioner has enough travel to compensate for the extra length. It is roughly 1/8" total.

Or, what is the max that I cam mill off of the boxes?

Advice please....

Thanks,
Jeff

You can get valve lash caps that fit over the top of the valve stem to take up the extra gap caused by smaller cam base circles. Guy Croft sells them in 1mm and 2mm thickness. There are also US suppliers that have them. Google "valve lash caps" to see what I am talking about.

[engineerted]

Jeff,
Don't machine the cam boxes, just make yourself some paper gaskets. Brown bag, paper is about 6-10 thousands thick, add a little gasket sealer and you are done. I have also just used rtv, no gasket, you just have to be carefully not to use too much other wise you run the risk of plugging the oil feed holes.

Ted

[pooldoctorstl]

I got a set of Alfa lash caps from a friend today and may use them but I am going to try the no gasket thing. I just measured the gaskets and they are about .9mm so that gets me in the 4mm shim range on the intake and 3mm on the exhaust. Maybe the aircraft case method of brown gasket maker and a piece of thread?

Thanks!!!

[rebar1111]

You might try using parchment paper(used for baking cookies and good up to 400F) instead of the paper bag material. It is thinner and will act as a release agent during disassembly.

[racydave]

Ted is right about the RTV sealant. GM used it a lot, and I have a lot of experience messin with it. It gives you a better fill given the variations. The surfaces gotta be spanky clean, with choke cleaner. I sometimes prep with some fine emery cloth and clean with some choke cleaner on a clean rag. I rub the sealant into both surfaces to make sure it is stuck. Use a thin coat.

[pooldoctorstl]

Ted and Racydave...thanks, that is my plan. I'll let you know how it all turns out.

Jeff

[engineerted]

Dave,

You hit the nail on the head. The key to RTV is getting the surfaces clean. RTV seals through adhesion, and the automotive industry uses Loctite 9400 on most of there engines, at least that is what we use here at Ford. You can buy the 9400, it is not cheap $34 tube, but I find that the Permatex ultra black hi-temp gasket maker is just about the same and a lot easier to find.

[BEEK]

my personal experience with lash caps is not good, we used them on a race motor, only to have one fail, it broke in half. i attribute that to a used shim bucket, which has wear and we did not machine the valve to either, all that i can say is it broke.

now i have milled cam housings many times with absolutly no issue, you do need adjustable pullies to adjust timing, but thats it. if there ever was a belt length issue, i was prepared to sleeve the tensioner and make it larger

[pooldoctorstl]

BEEK, that's what I was afraid of with the lash caps. I'll try no gaskets and then if I need to I'll mill the boxes a little.

Thanks for everyone's input!

Jeff

[Curly]

Lash caps were tried as a means of overcoming the small base circle of the race cams we used when we initially built the 1608cc engine for our tarmac rally AC coupe. Three out of the eight broke
The cam boxes were then machined to utilise the standard range of valve shims; but as expected, there was a problem with the belt tensioner running out of adjustment room. A slightly larger tensioner pulley was found and some extra movement was achieved by reducing the thickness on one side of the stud which runs up through the middle of the tensioner. Making a sleeve to increase the diameter of the tensioner pulley was to be our next move, but it wasn't needed.
As Beek mentioned, you will also need adjustable cam pulleys to enable the cams to be timed in back to their correct positions relative to the crankshaft.

[rebar1111]

Just checked the local paper bag for thickness. It varies from .005 to .015 inch in a 12 inch length. So while it may be ok for a water pump, it may not be for something as critical as valve clearance.

[pooldoctorstl]

I put it together with no gaskets and Ultra Gray RTV. Intakes are all in the 3.70 range and exhaust around 4.50. Not great but acceptable.

Jeff