Adjustable Cam Sprockets

[solarice]

Been randomly looking around at cam sprockets and the ability to advance / retard the cams.

Just been looking at Mulhollands and Aspect Racing's adjustables...

Mulhollands http://www.mulholland-rp.com/etc/sproket.jpg

Aspects http://aspectk11.web.fc2.com/CA5DEE9O1.jpg

Now Mulholland dont suggest the adjustment available...but Aspects site translates as :

March (K11) set of 2 for the sprocket
- changes the valve timing and a hole of about 5 degrees.
• To effectively utilize the high camshaft is by all means necessary.

Would people agree that they seem to suggest that each new hole is drilled at 5 degree intervals.?

Just i may have to make some up (for testing )...not that hard to drill a few holes especially as it appears they've devided up the 360 degrees into 8 points (including original).

Anyone have any thoughts on how close the valve to piston would end up? Mulholland says they're suitable for 256 degree cams and even include them with there own cams as a set...so id suspect clearance wouldnt be an issue for anything up to 256 degree (at max retard / advance)?

I know i could take the measurments myself from the engine and work out the sprocket degrees...but as im not making them just yet im holding off taking the car apart.

 

[frank]

with a 256 cam you could adjust the inlet opening event by at least 1/2 a tooth, i think kris (and the exh closing event)
and a stock cam will stand about 1 full tooth of adjustment before any contact :grinning:

 

[solarice]

ah ok...so how they getting away with the adjustment that appears to be available in the above pics? (its looking like maybe two teeth inbetween each point, to me anyway)...no mention on either site of needing other things for clearance, saying that they dont mention the cam lift either so probably not a suprise.

Though they do stock thicker head gaskets and iirc they also used to sell other pistons aswell (cant find them now). So maybe they're aiming for a multiple part buy.

Might have to get my old engine out (put it back together haha) and have a play...

 

[frank]

each hole uses a different "alignment dot" kris, so each hole is a fraction of 1 tooth apart in reality (you only need to move it, for example, 1/4 of 1 tooth, then 1/2 a tooth, then 3/4 of a tooth, then 1 tooth, then 1 and 1/4 etc, etc if you see what i mean :grinning: )

 

[solarice]

ah right yeah of course, with you now...

 

[r-reg-sr]

was this on the ebbdudes mods?

 

[solarice]

was this on the ebbdudes mods?

not sure tbh...will go and check.

Edit: Yup you're correct, I must have missed it. Not how i planned on modifying them mind...but interesting non the less.

http://www.micra.org.uk/threads/40439-quot-Maxi-Micra-quot-project....by-EBBdude./page3

 

[Stani1029]

Yeah ive copied ebbs sprockets, not took out as much as he has though. Only up to 1 tooth where as he has done 2 i think

 

[frank]

EBB is basicly running with no dowel eh (like me lol) infinate adjustment
there are 23 teeth, so about 31 deg of crank rotation per tooth, and the dowel slot lines up with a tooth, as does the timing dot
so 1/4 of a tooth (7.75 deg) of adjustment should suffice really

 

[solarice]

Never thought of running without the dowel lol...certainly the easiest way to make them adjustable. Just not sure how much i trust it.

Im actually sitting looking at a sprocket right now trying to work that out haha.

 

[frank]

Never thought of running without the dowel lol...certainly the easiest way to make them adjustable. Just not sure how much i trust it.

Im actually sitting looking at a sprocket right now trying to work that out haha.

i,ve been dowel-less for years kris lol :wasntme:
you can see in the pic that my misses,s inlet cam had to be advanced nearly 1/2 a tooth to correct the timing

 

[solarice]

haha.

Good good. Curious to try this as im sure theres power being wasted at the minute. Think i'll get a timing disc on the engine and see where everything ends up.

Hopefully i wont do it any harm.

 

[frank]

haha.

Good good. Curious to try this as im sure theres power being wasted at the minute. Think i'll get a timing disc on the engine and see where everything ends up.

Hopefully i wont do it any harm.

i find it better to measure how much the valves are open @ tdc kris (ie the amount of overlap, crutial for a forced engine like yours :grinning

 

[solarice]

Yeah, now i know the engine appears to be happy running boost *touches everything made of wood in sight* i can focus on being unsatisfied with its current power output and search for more lol.

If i can tweak a part of the engine, it'll be tweaked (so long as i can do it cheap...preferably free)

 

[Stani1029]

How exactly do you measure it frank? From the point it opens or from when the valve is at its furthest point. Need to learn more about this sorta stuff

 

[frank]

How exactly do you measure it frank? From the point it opens or from when the valve is at its furthest point. Need to learn more about this sorta stuff

with a vernier depth gauge stani :grinning: , i measure from the top of the cam bearing to the top of the shim/bucket when the valve is closed
then measure how much the valves are open @ tdc (stock valve timings are 16/0/0/16 for the 1.0, and 42/0/0/42 for the 1.3,s) so they should be set at 0 and 0 (ie, the inlet is about to open, and the exhaust has just fully closed) so no overlap
260 deg cams will have some overlap to scavenge the combustion chamber eh, so all 4 valves will be open about 1mm @ tdc