degreeing cam spec question and procedure

[recordsj]

MG Midget 1500.
In the manual it calls out the following:
Rocker Clearance: 0.010"
Timing (#7 and #8 valves): 0.050"
Inlet valve: opens 18 BTDC
close 50 ABDC
Exhaust valve: opens 58 BBDC
closes 18 ATDC

In the spec are the values for open/clos for when there is 0.050 valve movement? (i.e. inlet is considered open when there is 0.050 valve movement @ 18 BTDC)

 

[Brinkerhoff]

No, it means to degree the cam timing( with the valve train in place) you would set the rocker to valve clearance to .050" then with TDC found and your degree wheel in proper position the inlet valve should open at 18 degrees before TDC. You would need a dial indicator set on the valve to see it open. (reading the specs from your question). Are you setting the engine up or checking it? An easy way to check is with the valve cover off and at TDC on the exhaust stroke both intake and exhaust valves should be open the same amount . If they are open the same amount before TDC then your timing is early, if they open the same amount after TDC then your timing is late.

 

[recordsj]

Are you setting the engine up or checking it?

I am in the process of rebuilding (setting the engine up) the engine and putting everyting back to gether.

 

[Brinkerhoff]

Ok , do you have a degree wheel? A guy can do a lot of thinking with a degree wheel ... have fun !!

 

[recordsj]

got a degree wheel

 

[Scott_Hower]

got a dial indicator?

Factory cam or something else?

A degree wheel is great to have, but if you are using the stock gears, you don't have much adjustment to really "dial it in". You can get a 1/4 tooth adjustment (about 4-5 degrees I think) by changing the position of the cam gear on the cam (remove it, turn it 90 degrees, reinstall it). Same thing, but half a tooth if you flip it over.

 

[recordsj]

have dial indicator
not sure if it is a factor cam or not (no idea what other POs on this car has done...)

 

[Scott_Hower]

Without knowing the specs on the cam, you're kinda flying blind.

 

[Hap Waldrop]

Those are just checking points, kinda a lame way to have to degree a cam, what you would like to have is what most of us refer to as centerline of the came. Good cam suppliers will actually give you seocs to work with, one reason I do business with people like APT and Comptune on camshafts.

As mentioned, having cam specs and everything to degree a cam with is one thing, then you need a way to adjust the cam to the the desired timing, easier said than done on a 1500, a vernier cam gear is nice touch for this, since Triumph/1500 cams do not use keyways.

 

[Spridget64SC]

After 35+ years of racing and designing my own cams for 10+ years, I'm of the opinion for most applications; knowing the lift, the duration and the lobe centers is all that is necessary. With that information and remembering our high school mathematics, one can figure out everything else with a degree wheel, dial indicator and a dead stop. Find TDC using the dead stop and degree wheel. Then used the degree wheel and dial indicator to find out all the information you want. Most every cam ever ground for the A-series engine will work in the +/- 4 degree range of setting the cam in "straight-up". Straight up is when the center line of the intake is the same as the exhaust. This is pretty much the same for Triumph and B engines as well. 99.9% of the time, the cam is advanced to boost low end performance and compression is used to complete the top end.

For street applications, the lobe centers are usually wider than the race application. My guess is that a stock MG1500 cam is going to be in the 108 to 112 range. Probably around 110. Advanced would be 106 degrees. Anytime you play with cams in a racing application (high lift and advanced), need to double check the valve to piston clearance as well. Around +/- 10 TDC, the valves get pretty close to the piston.

As Hap said, having the cam specifications and the tools are one thing, being able to make adjustments is another. With the A & B BMC engines you have keys and Verniers. With the Triumph, only the Vernier makes the needed adjustment available. It is a rare cam that is ground exactly matching the attachment timing. Mixing gears from numerous engines might find you 1-3 degrees.

Also, most cam merchants won't tell you everything you want to know. They will usually tell you lift, advertized duration, lobe centers and running clearances. Some won't tell you anymore than where to set the cam into the engine and clearance. Keeps some of the "Magic" in the designs of their bumpsticks.


Mike Miller
Comptune
864-638-6316

 

[2091351]

After 35+ years of racing and designing my own cams for 10+ years, I'm of the opinion for most applications; knowing the lift, the duration and the lobe centers is all that is necessary. With that information and remembering our high school mathematics, one can figure out everything else with a degree wheel, dial indicator and a dead stop. Find TDC using the dead stop and degree wheel. Then used the degree wheel and dial indicator to find out all the information you want. Most every cam ever ground for the A-series engine will work in the +/- 4 degree range of setting the cam in "straight-up". Straight up is when the center line of the intake is the same as the exhaust. This is pretty much the same for Triumph and B engines as well. 99.9% of the time, the cam is advanced to boost low end performance and compression is used to complete the top end.

For street applications, the lobe centers are usually wider than the race application. My guess is that a stock MG1500 cam is going to be in the 108 to 112 range. Probably around 110. Advanced would be 106 degrees. Anytime you play with cams in a racing application (high lift and advanced), need to double check the valve to piston clearance as well. Around +/- 10 TDC, the valves get pretty close to the piston.

As Hap said, having the cam specifications and the tools are one thing, being able to make adjustments is another. With the A & B BMC engines you have keys and Verniers. With the Triumph, only the Vernier makes the needed adjustment available. It is a rare cam that is ground exactly matching the attachment timing. Mixing gears from numerous engines might find you 1-3 degrees.

Also, most cam merchants won't tell you everything you want to know. They will usually tell you lift, advertized duration, lobe centers and running clearances. Some won't tell you anymore than where to set the cam into the engine and clearance. Keeps some of the "Magic" in the designs of their bumpsticks.


Mike Miller
Comptune
864-638-6316

Mike, I agree!!

Do it right the first (and only) time!!!

Steve

 

[recordsj]

I assume with my degree wheel and dial indicator I can measure the profile of the cam by when the valve moves (to find when it opens and closes and find the center line of the cam)? So then I can figure if it is a stock cam or something else
I have an idea of how to do that, what would you recommend?

 

[Brinkerhoff]

Find TDC on the degree wheel . Then find when the intake opens and closes at the spec. lift. Find the same with the exhaust lobe. Stock ,the intake should open at the same degree ( though opposite) that the exhaust closes. That should give you at start point. Again a simple way to find this when assembled is at TDC intake and exhaust valves should be open the same amount ( lay a straightedge on top of the valves). Or do it with degree wheel and dial indicator.

 

[Spridget64SC]

The best write-up that I have ever seen, and read, is on the Iskendarian Cams web-site and in their catalog. Gives a straight forward story about how to degree cams and what everthing means and how adjustments affect performance.

Every time I'm in the Long Beach, CA area, I try and drop by an see Old Ed and Ron Iskendarian. Great guys. Hope to see them in July when I'm out that way for.

Just remember that where the keyways are cut and timing chain slack will affect the numbers. Cam and crank gear keys and keyways on the 1275, but only the crankshaft key and keyway on the MG1500 . With the 1500 engine, if the timing chain tensioner mounts in the timing cover, the chain will be slack if the cover is not on. You might have to make something up to tension the chain if you have the front T/C cover removed. Once you get the numbers, compare to the factory information and you can tell if you have a factory cam or not. Just adjust the center line of the lobes to what the factory states and do the math to move the opening and closing points and you can compare the cam profiles.

The lobe pattern and lobe centers on the ground cam are just locations in a 360 degree circle. Their position relative to the engine components is what counts. So, once you know what the cam looks like, you can adjust where it performs with everything else in the engine.

Mike Miller
Comptune
864-638-6316

 

[Hap Waldrop]

I assume with my degree wheel and dial indicator I can measure the profile of the cam by when the valve moves (to find when it opens and closes and find the center line of the cam)? So then I can figure if it is a stock cam or something else
I have an idea of how to do that, what would you recommend?

When degreeing a cam , you can clearly see the lift, duration and where the cam is currently timed at, now if you know what a stock cam is you can compare it to that.

Of course everything said here about keyways applies the A series engine but not the MG/Triumph 1500, as it does not use a cam keyway.

 

[recordsj]

how would I go about degreeing the cam if I don't know if it is stock or not?

 

[Hap Waldrop]

For starters use the degree wheel to check and see what you have now.

 

[recordsj]

MG Midget 1500.
In the manual it calls out the following:
Rocker Clearance: 0.010"

Inlet valve: opens 18 BTDC
close 50 ABDC
Exhaust valve: opens 58 BBDC
closes 18 ATDC

If I am using a dial gauge, would it be on the pushrod or on the valve cap (on the valve cap as opposed to the rockerarm) to what the above specs for when valves open and close are measured? I figure you are going to get different results since there is the 0.010" clearance between the rocker arm and valve (i.e. the rocker arm has to move 0.010" before it moves the valve).

 

[Scott_Hower]

You can measure either, but it's probably easier/more accurate to use the pushrod. To do the valve, you need to know the rocker ratio.

Have a look at Lunati's website. In the tech section.

 

[recordsj]

so if i degree the cam it by measuring with a dial gauge the lift of the push rods I just use the published open/close specs?

But if I degree it from the valve I need to do a conversion of the rocker ratio?

How would I do the conversion of the rocker ratio?