• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

TR2/3/3A Valve Timing Question!!

Share this page

Q

Quelch

Member
Offline
Hi Everyone,
I am in the process of installing the Moss narrow belt conversion on my TR3A. I followed the Moss instructions and made a new TDC mark on the replacement crankshaft pulley in the kit using a piston stop. Before marking this permanently the Moss instructions go on to say that it's prudent at this stage to verify the cam timing by turning the engine so that valves No. 7 & 8 are "on the rock" and seeing if the TDC mark I have made on the pulley corresponds. Mine seemed to be a few degrees out so I looked at the Haynes Manual section on cam timing which suggested setting the tappet clearances to 0.040" (for this test only) on valves No, 7 & 8. I did this and used a dial indicator to establish the exact point at which No. 8 tappet stopped moving and No. 7 started to depress.
The end result is that my No. 7 & 8 valves are in the rocking position at 2 to 3 degrees BTDC on the crankshaft and not right on TDC as I assume they should be. Is this an acceptable error or should I be looking to get this right smack on TDC!!
One other thing. My ignition timing was set by trial & error last summer. I was experiencing a lot on pre-ignition so I continued to retard the timing until the pinking stopped. Earlier today I checked the ignition timing (before anything was disturbed with the narrow belt conversion) and noticed that it was reading only 2 degrees BTDC (easy with the rad and apron removed) and not 4 degrees as it should!! I was wondering if these two issues could be connected.
Anyone's advise on this would be greatly appreciated.


Regards, Neil.
 
Quelch said:
Hi Everyone,
I am in the process of installing the Moss narrow belt conversion on my TR3A. I followed the Moss instructions and made a new TDC mark on the replacement crankshaft pulley in the kit using a piston stop. Before marking this permanently the Moss instructions go on to say that it's prudent at this stage to verify the cam timing by turning the engine so that valves No. 7 & 8 are "on the rock" and seeing if the TDC mark I have made on the pulley corresponds. Mine seemed to be a few degrees out so I looked at the Haynes Manual section on cam timing which suggested setting the tappet clearances to 0.040" (for this test only) on valves No, 7 & 8. I did this and used a dial indicator to establish the exact point at which No. 8 tappet stopped moving and No. 7 started to depress.
The end result is that my No. 7 & 8 valves are in the rocking position at 2 to 3 degrees BTDC on the crankshaft and not right on TDC as I assume they should be. Is this an acceptable error or should I be looking to get this right smack on TDC!!
One other thing. My ignition timing was set by trial & error last summer. I was experiencing a lot on pre-ignition so I continued to retard the timing until the pinking stopped. Earlier today I checked the ignition timing (before anything was disturbed with the narrow belt conversion) and noticed that it was reading only 2 degrees BTDC (easy with the rad and apron removed) and not 4 degrees as it should!! I was wondering if these two issues could be connected.
Anyone's advise on this would be greatly appreciated.


Regards, Neil.
Click to expand...

I did the same Moss fan eliminator kit awhile back.I did not concern myself with cam timing as the pulley indicates crankshaft position.I think I just used the keyway center(or 180 opposite,I forget)same as the original sprocket to match the original TDC hole.Then I did the math and marked TDC 4,8,&34BTDC degrees on the pulley with chisel.
Tom
 
Quelch said:
The end result is that my No. 7 & 8 valves are in the rocking position at 2 to 3 degrees BTDC on the crankshaft and not right on TDC as I assume they should be. Is this an acceptable error or should I be looking to get this right smack on TDC!!
Click to expand...
Should be fine. The factory adjustment only moves in increments of 4 degrees or so, and slightly advanced is better than slightly retarded. It will retard slightly in operation anyway. Even 4 degrees of error will only shift the power band by 500 rpm or less; the engine will run just fine.
Earlier today I checked the ignition timing (before anything was disturbed with the narrow belt conversion) and noticed that it was reading only 2 degrees BTDC (easy with the rad and apron removed) and not 4 degrees as it should!! I was wondering if these two issues could be connected.
Click to expand...
I doubt they are significantly related. In any case, 2 BTDC isn't far enough off the factory spec of 4 BTDC to worry about, IMO. It just isn't all that critical.
 
As the timing chain stretches over time and the teeth of the sprockets wear down, the cam timing will retard on it's own, so starting out a little advanced is a good thing in my book.
 
When I rebuilt my engine, the cam came out about 2 degs. advanced also. What you might want to do when marking out the TDC mark on the new pulley is to also make a mark 180 deg opposite. This helps a lot when setting the valves.
 
In general, advancing the cam timing in relation to the crank moves the power band to a lower RPM. Retarding the cam timing, likewise, moves the power band up in RPM. I would be very happy with 2 degree advance in a new rebuild.
 
Back
Top