13 replies to this topic

[andyt]

When i rebuilt my mg metro engine i had the 65m electronic distributor re curved by Ac Dodd and refitted it in the same position as i had on my previous 998 build with the drive slot at the 8 to 2 o'clock position, i had the car rolling roaded and was told that the cam timing was way out,( AC had given me the figure to time the cam in at and I trust the information that he gave me} now i had been pretty meticulus when setting the cam timing and was very dissapointed with the result although i was sure i had correctly set the timing. At the weekend i picked up a copy of the metro Haynes manual as it has the MG supplement which covers the engine and ignition settings for the engine that i have fitted, now i have found a section and diagram which explains that when fitting the 65m distributor that the drive should be fitted with the slot fitted further round in a clockwise direction, i have now done this and would like to know if this was the cause of the cam timing seeming to be incorrect?

 

All of this has been very frustrating as i was pleased with the performance of the home built engine but the rolling road operator has really put a downer on what i thought i'd done well.

 

 

[nicklouse]

the dog drive is off set by some degrees. just fit the drive in the engine so that the amplifier box clears things.

[Dusky]

How does the RR guy know the cam timing without opening the engine?

[Cooperman]

The only way to determine whether the cam timing is incorrect is to accurately measure it.

There is a way to check it to within a few degrees without taking the timing cover off. You bring the nos.1 & 4 pistons to TDC (or to the established TDC marking if you have one. Mark the position of the crankshaft front pulley. Measure the diameter of the crankshaft front pulley and multiply it by 3.142. Divide by 360 and multiply by the ATDC angle at which the cam should have maximum lift on inlet valves (maybe 110 degrees). 

Remove the rocker cover and determine whether it is firing on 1 or 4. Put a DTI on top of the inlet valve on the firing cylinder. Rotate the engine in the normal direction until that valve is fully open and mark the position of the front pulley relative to the position at TDC.

Now measure around the radius of the TDC position to the valve fully open position and compare it with the radial length you just calculated. You can do this to within around 0.1" if you are careful.

For example, if your pulley is 5" diameter and your cam timing is 106 degs ATDC, the radial dimension should be:

5 x 3.142 = 15.71". Divide that by 360 and you get a radial distance of 0.0436" per degree. Multiply by 106 and the correct radial distance should be 0.0436 x 106 = 4.62"

Since on a road engine you can allow a tolerance of around +/- 2 degrees, so long as you measure to within +/- 0.10" and it comes up at between 4.5" and 4.65" your cam timing is acceptable and you have probably set is absolutely right.

 

Now, with regard to the distributor, set the slot angle to the setting shown in the Haynes manual and fit the distributor. Bring the pistons 1 & 4 back to TDC and turn the engine back around 6 degrees. You can use the calculations above to work out what 6 degrees is.

Fit the rotor arm and turn the distributor body until the rotor arm is pointing to one of the terminal posts inside the cap. The lead for that terminal goes to the plug for whichever cylinder is firing which you can tell from the valve positions.

[nicklouse]

, now i have found a section and diagram which explains that when fitting the 65m distributor that the drive should be fitted with the slot fitted further round in a clockwise direction, i have now done this and would like to know if this was the cause of the cam timing seeming to be incorrect?

 

nope it has nothing to do with the cam timing it is because the dog on the dizzy is 21 degrees out of like with the rotor arm you will find in the Haynes Mini manual as well in the supplement section. many people forget this difference. but to be honest the position has little effect on anything as you just set it accordingly.

[Spider]

How does the RR guy know the cam timing without opening the engine?

 

If he's worth his salt, he'd know to within +/- 5 degrees.

 

On a lot of cars, I can tell when I drive them if the Cam timing is out.

[GraemeC]

Good explanation Cooperman.

Just to be picky though, ifs circumferential distances you’re measuring, not radial.

[andyt]

He had me rev the car whilst he checked the timing and then told me there wasn't enough advance and then proceeded to turn the distributor forward and back all to no avail.He repeatedly told me that the cam timing must be way out and that was that!

[nicklouse]

sounds like a person who has little idea.  I would find another Rolling road. but before that get yourself a timing light and set your timing.

[ACDodd]

He was measuring ignition advance which of cours is nothing to do with cam timing!!!

It sounds like the ignition advance curve in your distributor is not working(seized) or completely mismatched to your engines requirements. This is very common.
Send me a pm if you want someone to check over your unit and if needed provide you with a more suitable unit.

Ac

[nicklouse]

He was measuring ignition advance which of cours is nothing to do with cam timing!!!

It sounds like the ignition advance curve in your distributor is not working(seized) or completely mismatched to your engines requirements. This is very common.
Send me a pm if you want someone to check over your unit and if needed provide you with a more suitable unit.

Ac

read the OPs first line. you have already done it. ;)

[andyt]

AC I have pm'd you

[ACDodd]

Ah yes I see that now. Unlikely to be the advance curve then!!

Compression test the engine, and perform a cylinder leakage test. Post back the results.


Ac

Edited by ACDodd, 31 August 2018 - 06:37 PM.

[Dusky]

How does the RR guy know the cam timing without opening the engine?

If he's worth his salt, he'd know to within +/- 5 degrees.

On a lot of cars, I can tell when I drive them if the Cam timing is out.

But you are special