SAH cam - valve clearances?

[88V8]

Only three posts?!!!

If the TR5 is that reliable, maybe I should have bought one rather than a TR6

 

So why am I posting on the TR5 website when I have a TR6...

 

Because I have a long-running problem with the brakes (TR6 It Servos No useful Purpose) and have only this minute found the cause, which is that the manifold vacuum is only 6 in Hg at a 700rpm idle (should be 12.5 in Hg with a PI car). Hence virtually no servo.

 

In the engine, as from 1976, is a what the owner who had the work done describes as an 'SAH medium cam'. The profile, he recalled, was 'like the TR5'.

 

Now, the subsequent owner-muppet from whom I bought the car has lost all the data sheets, so I don't know the correct valve clearances. At the moment I'm running the standard TR6 clearance, ie 10 thou. If this is too tight, perhaps that partly accounts for the low vac?

 

The engine had a lot of other work done, including porting, polishing and higher comp - don't know how high - and idles very lumpy.

 

Compressions are in the region of 220psi (yes, two hundred & twenty) - hot to first fan cut-in, 12 seconds, full throttle.

 

So, question: does anyone have any idea what the valve clearances should be?

If not, what's the standard clearance for the TR5 please?

 

Ivor

 

PS as the TR6 site is so busy I'll also post this thread on there......

[piman]

Hello Ivor,

 

I have a SAH cam in my 2.5 saloon SAH 1010 (Type 307), 30-70/70-30 and the clearances are 0.010" inlet and 0.011" exhaust. By comparison, a TR5 and early TR6 is 35-65/65-35, I don't have a TR5 manual so don't know the clearnces but would guess 0.010" for both?

 

for you information my idle vacuum is 7 to 8"HG but my compression pressures are much less, more like 155psi or so.

I also have a vacuum reservoir for the brakes, do you?

 

 

Alec

Edited January 8, 2008 by piman

[paul gardner]

As i understand the system, manifold depression for TR5 andTR6 CP series is 7-8" Hg; for CR series engines it should be 12" Hg.

Yours

Paul

[Tom Fremont]

I would side with Paul and Alec whose posts impliy you have yet to discover the fault with your brakes

 

My (2) reference points are a P.I. cam with ~ 10:1 c/r and another with a little more overlap 41/71/71/41 and 0.508" lift (!) and 10.7:1 c/r. Neither suffer from lousy brakes , and the former will idle at ~ 550 or so.

 

I am befuddled by the high compression numbers you got - the more the overlap the lower the readings...

 

As for the cam, the factory P.I. as well as the others issued for TR250/6 are to be set at 0.010". However, I wouldn't for a moment trust this value to apply to any aftermarket cam ( of which all I've seen have larger clearances ). So your best bet is to track down the SAH recommendation.

 

We're all quite curious about your brakes I'm sure

Edited January 8, 2008 by Tom Fremont

[Bob Stubbs]

Ivor

 

For what its worth, I have a slightly hairy Fentune cam in my 6. Like your muppet previous owner, I didn't get any data sheets for the cam and its no longer made, but I did know that the 10 thou clearance was wrong as the performance was awful. Eventually tracked down the info and found out that it should have been 16 thou inlet and 18 thou exhaust...............just a slight difference eh?

[graham.dillaway]

Just to add my tuppence worth - I have an American spec TR6 and I upgraded the engine several years ago. The cam shaft I put in was a BP270 and all clearances - exhaust and inlet are 17thou. I was told this by the person I got the cam shaft from and I wrote it down on a scrap of paper as I did not get any offical data.

 

I can understand how this info can be 'Lost' in selling a car. I did not get any official reference data with the cam shaft.I wote the info down on a scap of paper following a conversation with the supplier.

 

Anyway I was wondering if you do not know what has been done to the engine and what cam shaft has been fitted is there any way of finding out what should the valve clearances should be?

 

regards Graham

[88V8]

I am befuddled by the high compression numbers you got - the more the overlap the lower the readings... Tom Fremont

Yes, so am I.

I hate to think what the CR must be. No wonder it 'runs on' a bit atm, despite starting to back off the static timing.

Presumably there is some way of calculating the CR from the compression readings? I suppose if one knew the chamber volume - Physics, anyone?

 

if you do not know what has been done to the engine and what cam shaft has been fitted is there any way of finding out what should the valve clearances should be?

Graham

 

Maybe, in my case, as I do at least know that it's an SAH cam. And I learned this morning what you erudite chaps may already know, that SAH became Triumphtune became Moss.

And on the Moss website are details of all the Triumphtune cams they sell - overlap, timing, lift, and valve clearances. The clearances are mostly in the range 14 - 24 thou.

So now I need to spec out the cam in my own engine, and if it matches one of theirs, then, perhaps, bingo. Assuming they haven't changed the ramp profiles in the intervening 30 years. I am waiting to speak with Geoff Marks at Moss who hopefully can tell me.

 

Whether this will fix the brakes, taking on board some of the posts subsequent to this Eureka moment, well, hmmm.

But at least it may save frying the valves.

 

Ivor