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Stock Cam Timing

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Morris

Morris

Yoda
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I am getting ready to put the stock cam back into my Midget 1500. Last time I use the timing marks to line everything up, and it seemed to go okay, but I am wondering if I can do better.

How can I check my cam timing to make sure it is dead spot on? Step by step instruction would be extremely helpful.
 
You will need a degree wheel, dial indicator and a base stand.

I have done it this way for years, but other forum members have told me that it is not necessary for a street going LBC.

If you need to purchase these items, I would recommend the old fashioned method.

Patrick
 
There's a nice bit on cam timing at minimania here. It sort of requires knowing the specs, but there is something about aligning equal lifts of inlet and exhaust valves at tdc.

I get to do this myself sometime soon, but I'm using a Kent cam with different lift and duration for inlet and exh. If you are using a standard cam, it is most likely the same lift and duration for both.

Donn
 
I have a dial and base. Is a degree wheel something I can pick up at my local auto parts store?
 
They may have it, if not any reputable place should. They are not that expensive.

I basically do it the same way as Donn's link, but without the head installed and using pushrods instead. This allows me to insure that I have TDC by putting the indicator on the piston.

Also for A series we use offset keys to adjust, I am unsure what the Rumph engine uses.

Patrick
 
With the gear I have, it seems the only adustment I can make is to move the chain over a tooth.
 
That would be too much.

Moss pn 327-220 should be sold by someone for your engine in 1-8 degree offsets.

Not being a 1500 guy, I do not know where you could get one.

Patrick
 
spitbits?
 
GB1 said:
You will need a degree wheel, dial indicator and a base stand.
Patrick
Click to expand...

You can do without the dial indicator if all you are doing is finding the lobe centers and then adjusting the timing. You just need some way of finding TDC: a stop or even a pencil riding up and down on the piston crown in a spark plug hole will do. A dial indicator is only required if you are going to measure lift or to check the timing at some specified amount of valve opening. Simply "degreeing" a cam can be done without much investment in precision measureing tools if you are a "shadetree mechanic".
 
I was going for the most accurate method that I know of, I believed that this is what Morris was looking for.

Patrick
 
WestfieldVII,

Could you please give a step by step description of how to degree a cam shade-tree style?
 
Morris said:
With the gear I have, it seems the only adustment I can make is to move the chain over a tooth.
Click to expand...

I am not 100% positive on this, but i think you will find that you can reverse the cam sprocket and also rotate the sprocket thru 180ÂŞ to make finer adjustments.


mark
 
IIRC I used a pencil with a line marked on it to indicate the piston position. Attach your degree wheel to the crank pully along with some sort of a pointer so that you can accurately indicate timing. Don't worry which number the pointer points to yet.

Now rotate the crank in the normal direction watching the pencil in #1 cylinder go up and down, sighting across the edge of the plug hole will allow you to stop the crank as your mark on the pencil lines up with the edge of the hole. Write down your degrees indicated by the pointer and continue to turn the crank as the pencil rises with the piston. It will reach TDC (top dead center) and begin to fall as the piston drops. Watch for your mark on the pencil and stop the crank when the pencil lines up exactly as it did before. Now write down the number from your degree wheel. Half way between the 1st and 2nd measurement is TDC. Repeat a couple of times to verify you are correct and stop the crankshaft at the number you calculated to be TDC.

Loosen the degree wheel and rotate it until the pointer reads 0, now the degree wheel is set to top dead center #1 cyl on compression stroke. Use the same method as before to find the degree at which the intake valve opens on #1 cyl, only use a thin feeler gage to feel when the cam lobe begins to touch the valve. Check the reading when the valve opens and again when it closes releasing the feeler gage. This will tell you lobe center of the cam.

A couple things to note:
1. Always turn the engine in the normal direction of rotation. If you go past your mark and have to rotate backwards, go back a 1/4 turn before proceeding again in the correct direction. This will remove any slack in the valvetrain and give a more accurate reading.
2. Make sure that #1 cyl. is on compression be checking the rocker arms for looseness. Intake and exhaust valves will both be seated with loose rockers on compression stroke.
3. It may be a bit easier to check the valves by introducing an extra bit of clearance to the valve adjustment, perhaps .010" or so.


I hope any readers will correct anything I may have left out.......
 
This is great! Thanks!

Once I know "lobe center" how can I use that knowledge to tell if my cam is properly timed?
 
If you match up the dots and then degree the cam you should see something in the 108-110 range give or take, if you're a tooth off that something like 16 degrees if I'm not mistaken, so you'll know you are wrong by your degree wheel readings. Try getting about a 3 degree off set keyweay, and advance the cam, this will wake up the midrange acceleration of the motor, pretty common with race cams and performance street cam, so the same thing should work for a stock cam. Most of the performance street cam I use in motors are on a 106-108 center line, most race cam 102-104, so expect the stock cam to be a little more than the performance street cams. With the cam in the block and a degree wheel mounted you can find out anything you want to about a cam, lift, centerline, duration etc..
 
Sorry for being a dunder head, but I want to make sure I understand this...

I found these specs for a stock 1500 cam on Paul Teglar's site.

Seat Duration: 247°
Intake: 18-58°
Exhaust: 58-18°
Lobe centers: 112°


So, if I use the techniques described above, starting from TDC before the intake stroke on #1, my intake valve should open at 18 and close at 58.

Right?

Starting from the same place, I could check the exhaust on #4, and it should open and close at the same time... right?
 
Sadly, I don't have a BMC camshaft. Mine is a BL. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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