Putting an early rounded cam cover on a Mk2 type engine = ADVANCED inlet cam timing..... ?

[DeadZedDave]

A Mk2 type engine fitted with an earlier "round type" cam cover needs to have the camchain top idler assembly swapped to the earlier type because the Mk2 style one will not clear the early cam cover.

I've read / heard this many times and done it myself on more than one occasion !

Lots of people have done this over the years and many of us prefer the "original look" of the round cam cover over the square shape Mk2 cover.

I'm looking at a Mk2 top idler pulley next to an A1 type and can see theres a height difference - the actual idler wheel on the Mk2 sits a couple on mm higher - no doubt to allow for the extra tooth on the cam sprockets (?)

However, the A1 top idler fitted on the Mk2 head pulls the cam chain down more between the cams - the result is the inlet cam gets advanced by some degrees....

Has anyone got a figure for the number of degrees that this will advance the inlet cam ??

ALSO Is there a rounded cam cover that fits the Mk2 ?? .... I think I can remember one time fitting a cover - I think it was from a Z1R and with one casting rib inside ground away it fitted .... I could be wrong !!

[Z1streetfighter71]

To help your search, the 14025-1119 Cam cover is all the same on the Z1000's up to the Mk2 change over.

[Z1streetfighter71]

I have all cam covers at hand and cylinder heads if you need any comparisons.

[DeadZedDave]

Thanks for the swift reply Z1streetfighter71. I have some cam covers / heads / top idlers etc. and it looks like the earlier A1/A2/D1 idler is needed for the round cam covers if you put them on a Mk2 - which is what several sources say, (theres at least one post on this forum !) This is also mostly what I remember ! The idea that I once found a cover which fitted might be just my bad memory !
I'm hoping that in the 40 odd years since these bikes were made - and all the times people have done this mod. that somebody will know by how many degrees the inlet cam gets advanced !

[chrisNI]

If you use adjustable cam sprockets can you not set the cam timing to whatever it should be?

[DeadZedDave]

You're right of course ChrisNI ! It's just that I wondered if anybody knew the answer !
Its a mod that I'm sure will have been done many times - Mk2's were not always popular !!

[zed1015]

Thanks for the swift reply Z1streetfighter71. I have some cam covers / heads / top idlers etc. and it looks like the earlier A1/A2/D1 idler is needed for the round cam covers if you put them on a Mk2 - which is what several sources say.

This is why the early idler design is used by APE and LISKA etc for their race item because it fits all and most time they are used in conjunction with slotted cam sprockets so the idler height difference isn't an issue but in the absence of slotted sprockets you should use the idler of the correct height or use a spacer.

As for the intake advancing, a couple of degrees or so won't make too much difference but i haven't a clue how many degrees the different idler heights make as i either use the correct one or build my engines with slotted sprockets and degree them in.

Intake Advance General Effect
Improves low-end power and throttle response
Intake Valve Opens sooner
As general rule 4 degrees advance moves peak torque 200 rpm sooner.

[chrisNI]

This is why the early idler design is used by APE and LISKA etc for their race item because it fits all and most time they are used in conjunction with slotted cam sprockets so the idler height difference isn't an issue

That explains why I didn’t have an issue with my Z1000 I suppose it’s got a mk 2 crank and the standard cam cover etc. but the top idler hardware is all Liska.

[DeadZedDave]

Thanks once again for swift responses !

I can't argue with zed1015 when he says "use the idler of correct height" (which is correct for the engine) - wise words !

The idea of a spacer to lift the height of the A1 idler is something I've looked at but it quickly runs out of room under the early cam cover..... two gaskets can be used to lift the cover for more room but it starts to look a bit odd.

The following is great advice however - thanks again zed1015

"Intake Advance General Effect
Improves low-end power and throttle response
Intake Valve Opens sooner
As general rule 4 degrees advance moves peak torque 200 rpm sooner."

I'M ASSUMING THIS IS "CRANKSHAFT" DEGREES ?
It's a good "rule of thumb" to work with !

This also helps explain a lot. I've previous experience of a couple of Mk2 engines done this way and recollection was they had strong midrange - though at the time I wouldn't have questioned or known why ! My "guess" from visual examination (of an example I still have today) is that these engines are probably running with something getting close to half a tooth space advance (on the cam sprocket) which is quite a lot ! - THIS IS THE REASON WHY I'M ASKING THE QUESTION - "idle curiosity" maybe but it would be good to know.

Memory and experience, as well as online information, tells there will be a good number of Mk2 engines out there with the round cam cover fitted and many of these I'm sure will have been done without degreeing the cams or any other mods. These were just old bikes in the mid 80's /90's and before we had internet, if the bloke down the pub / local expert said "just change the cover but you need the top idler as well" then thats just what happened ! Lots of owners wouldn't have known anything about lobe centres or slotted cam sprockets and probably wouldn't have had the necessary tools or skills to do the work anyway !

If anybody has some numbers it'd be interesting to hear.....

[zed1015]

You should just keep the correct height mk2 idler and clearance the cam cover.
The only mechanical difference between all the round covers is the tower in the middle.
Early Z1 ones are straight and plain and later ones have a bulge either side to clear the sprocket bolt or rivet.
For the mk2 idler use this later type of cover and trim the internal rib.

s-l500 (3).jpg (18 KiB) Viewed 1943 times

[DeadZedDave]

Hello zed1015 - I had a "lightbulb moment" when I read your latest !!
I originally wrote : "ALSO Is there a rounded cam cover that fits the Mk2 ?? .... I think I can remember one time fitting a cover - I think it was from a Z1R and with one casting rib inside ground away it fitted .... I could be wrong !!"
Suddenly I remember it clear as day.....
I guess the "how much is the cam advanced" question becomes academic.....
Thanks for your response / help

[Al]

Approximately.
The centre idler pulls the chain down by 2mm in the centre as stated.
This could be seen as equivalent to 4mm; 2mm per side of the ‘V’
Chain pitch, i am guessing conveniently at 8mm but have no clue, i havnt seen one for ten years.
Therefore sprocket is advanced by half of one tooth.
There are 32 teeth on the MKII cam sprocket and 360 degrees on the crank.
360 divided by 32 teeth gives 11.25 crank degrees per cam wheel tooth.
Cam wheels rotate at half engine speed so divide by 2.
11.25 degrees at the crank / 2 equals 5.65 degrees crank rotation per cam wheel tooth actual.
We are estimating; half a tooth, so divide by two again equals 2.81 crank degrees for half a cam wheel tooth.
I don’t have; cam open and close figures for a MKII camshaft so have used Z1000 J1 open and close values from the factory manual. It makes no difference to the value of the change though naturally the numbers themselves will be different for the MKII camshaft.
J1 cam timing equals 105 Lobe Centre (LC) degrees on inlet camshaft.
Standard J1 Opens 35 degrees BTDC becomes 37.81 degrees after advancing half a tooth of a 32 tooth MKII cam wheel.
Standard J1 Closes 65 degrees ABDC becomes 62.19 degrees after advancing half a tooth of a 32 tooth MKII cam wheel.
Larger number plus 180, minus smaller number, then divide by 2 equals 102.19 LC
62.19 plus 180, minus 37.81 divided by two becomes 102.19 Lobe Centre
Standard J inlet camshaft is 105 LC, therefore 3 degrees LC change for half a 32 tooth cam wheel advance.

AL

[DeadZedDave]

Thanks Al ! Application of logic wins every time.
Makes perfect sense but I'll wait until I've got a fresh head on before I put the Mk2 cam numbers in and take my shoes and socks off !!
I imagine somebody out there will know the answer to the sum already or perhaps have measured the value using the dead stop and dial gauge with the old degree disc but I suppose it matters not !
Thanks again, Dave

[Al]

Re-worked with some more realistic numbers Ver.2

Approximately.

The centre idler pulls the chain down by 2mm in the centre as stated.
This could be seen as equivalent to 1.6mm overall; 0.8mm per side of the ‘V’
(Google trigonometry calculator)

Chain pitch, is 7.77mm.
Therefore sprocket is advanced by 1/5 of one tooth ( 4.85 rounded) on a 32 tooth MKII sprocket.
There are 32 teeth on the MKII cam sprocket and 360 degrees on the crank.
360 divided by 32 teeth gives 11.25 crank degrees per cam wheel tooth.
Cam wheels rotate at half engine speed so multiply by 2 as crank travels at twice speed of cams.
11.25 degrees at the cam wheel x 2 equals 22.5 degrees crank rotation per cam wheel tooth actual.
We are estimating; 1/5 of a tooth, so divide 22.5 again equals 4.64 crank degrees for 1/5 a cam wheel tooth.

Z1000 (1015 motors) valve timing figures are;
Inlet opens 30 degrees BTDC
Inlet closes 70 degrees ABDC
This gives a standard 110 Lobe Centre (LC) for the MKII camshafts
Advancing the inlet for opening gives a new number at 34.64 degrees
Advancing the inlet for closing gives a new number at 65.36 degrees

Larger number plus 180, minus smaller number, then divide by 2 equals 105.36 LC
(65.36 plus 180, minus 34.64 divided by two becomes 105.36 Lobe Centre)

It looks like the advance in the inlet cam wheel alters the standard 110 LC to 105 LC which seems excessive to me but there it is.

AL

[DeadZedDave]

Thanks again for some more number crunching Al.
I believe there'll be one or two engines out there with this set up from back in the day so its very useful to have a number to put on it.