9 replies to this topic

[Pickwah]

Quick question regarding offset woodruff keys for accurate cam timing..

Im fitting a new set off duplex gears along with a new chain. Ive measure my cam timing using a dti and have the following measurements;

112 degrees at maximum lift after tdc.
The readings from either side of the cam lobe (0.005 either side) 97 & 127.
97+127=224 / 224 divided by 2 = 112degrees.

Question is, with my average being the same as my maximum lift, is any adjustment required? Reason I ask is that Rover quote 110deg from tdc for the particular cam Im using. I also want to allow for initial chain stretch which I believe is 2-3degs.

Thanks in advance 😁

[Spider]

On the basis that the cam lobe profile is symmetrical, then your measurement method is right.

 

I do like to wind them over a good few times (like around 50), with some load on the cam, to get the chain and sprockets settle before taking measurements.

 

I allow a 2 degree initial advance to compensate for further settling, stretch and some wear.

 

On this basis, you'd be needing a 4 degree key.

[Pickwah]

I had an inkling that a 4deg key would be needed, 2 for the initial advance and 2 more to allow for the stretch. Am I thinking this is correct?

[Steve220]

This has got me worried now, as my cam timing is utterly bang on and i didn't turn the engine over loads before hand, but its quite tight and i've turned it over only a few times.

[Spider]

I had an inkling that a 4deg key would be needed, 2 for the initial advance and 2 more to allow for the stretch. Am I thinking this is correct?

 

Yeap

 

This has got me worried now, as my cam timing is utterly bang on and i didn't turn the engine over loads before hand, but its quite tight and i've turned it over only a few times.

 

Good work for checking and setting, however, with a Chain Drive, it can only go one way from there - retarded.

 

This may not be a bad thing though, nor the end of the world.

 

Depending on the engine spec, I've found changes of 2 degrees to be noticeable and with some, quite so.

 

Generally speaking, with many Cam Profiles and Engine Specs - Advancing Cam Timing will produce better power at lower engine speeds however, the best potential of the Cam is rarely realised when timed this way. This can be a way of taking the 'edge' off a wild grind to make it more livable for the street as it will come on the cam at lower revs. Be careful though with going too far that the Inlet Valves don't kiss the Pistons,,,,,Also, be careful with the DCR when going this way.

 

Likewise, when Retarded, it pushes the peak power further up the revs (at the expense of that lower down) and will usually produce more power.

 

For what ever it's worth - and just how I like to run my engines - I tend to Advance most grinds, some by as much as 6 degrees.

[Cooperman]

As produced by BMC (or whatever they were calling themselves at the time) the standard for cam timing was not very good. I have seen original timing as much as 5 degrees out. When new cams and sprockets are fitted and timed dot-to-dot the timing can be even more incorrect.

The cars still run ike that, but just not as well.

Modern cars have super accurate machining, but when the classic Mini was produced some new cars went much better than others. This, I have always believed, was due to the adverse build-up of manufacturing tolerances and especially the cam timing.

Woodruff keys do remove this problem, as do vernier sprockets.

[hhhh]

And the longer the duration, the more important the accurate timing is because the timing of the events can start to get ridiculous.

[Cooperman]

And the longer the duration, the more important the accurate timing is because the timing of the events can start to get ridiculous.

Absolutely right. Any cam beyond, say, a Kent 276 will perform noticably less well if not accurately timed in.

 

I did a check on duplex chain stretch a few years ago. It stretched 1.5 degrees in the first 1000 miles, and at c.2000 miles it had stretched 2 degrees.

[Midas Mk1]

As above, even with a Iwis chain I had to advance mine a couple of degrees to take account of chain slack. When I first had my sw10 dyno'd i was told to check the timing as it was thought it lost a little timing When checking I had to advance it a couple of degrees, the difference it made, wow. Using the sw5 with the saw technique made good results!

[Steve220]

Glad my engine is still out! Will give it some advance.