Shim Clearance and Timing Check

[blaat!]

The workshop manual specifies 0.15mm for the intake clearance and 0.30mm for the exhaust clearance on a Mach 1:

wm2.JPG

A timing check follows to ensure all the timing components have been assembled correctly and nothing is an incorrect component or worn beyond spec. During this check it says to use a feeler gauge, however the gauge size specified is larger than the gap - 0.25mm for the intake and 0.40mm for the exhaust:

wm1.JPG

Is the text incorrect? Am I supposed to jam the over-sized feeler gauge in and do the check anyway? Am I missing something?

Thanks!
Jim

[DewCatTea-Bob]

" During this check it says to use a feeler gauge, however the gauge size specified is larger than the gap - 0.25mm for the intake and 0.40mm for the exhaust:

Is the text incorrect? Am I supposed to jam the over-sized feeler gauge in and do the check anyway? "

____ I don't know exactly what your source is but, what size is the "specified" feeler-gauge ?
(As I do the math, it seems it ought to be .1mm-thick.)


Dukaddy-DUKEs,
-Bob

[LaceyDucati]

The idea is to use a 4 thou gauge (0.1mm). The manual makes a big song and a dance explaining a simple procedure. Basically it means open up the running clearances by 4 thou, then use a 4 thou gauge to feel the valve opening or closing.

For example a Mach 1 has a specified running clearances of 6 and 12 thou (0.15 and 0.3mm). Checking clearances are 10 and 16 thou ( 0.25 and 0.4mm) with a 4 thou (0.1mm) gauge in the gap.

Don't expect particularly accurate results for timing, Ducati only specified + - 5 degrees and that's hopeful!

Checking timing on initial lift is not that accurate as the rate of rise is slow. For me figures at 0.5mm or 1mm are better.

Nigel

[blaat!]

Ahh, got it. Thanks Nigel. I'll try checking the numbers using the correct method and see if they come in any closer

[blaat!]

After thinking about this for a while... The shim cap rotates freely on the valve stem when the motor is at TDC because there is the target gap - 0.15 mm intake and 0.30 mm exhaust.

At the moment the cam closes that gap and puts the slightest amount of force onto the shim cap it should no longer rotate freely on the valve stem.

Shouldn't this give me the same degree results as acquiring two more smaller shim caps that are -0.1 mm and using a +0.1 mm feeler gauge?

[LaceyDucati]

Sort of yes! But it is all a bit airy fairy and how much feel you will get is debatable. The other thing you can do is put a clock gauge on the top retainer.

Problem is if you do the feeler gauge thing and put a clock gauge on the retainer, sometimes you will observe when the gauge is gripped gently you can swing the engine through quite a few degrees before much happens! Hence the covering themselves + or - 5 degrees. I'm not convinced the accuracy of these checks. Mostly you can convince yourself that it's correct with the + or - 5 degrees and a bit of turning a blind eye

Working out the lobe centres from the factory design figures and then taking 1mm figures and working out the actual lobe centres you have, can help provide more data to compare to.

It should also be remembered that if there is any significant play in the bevel gears (especially between the gear shafts) you will get odd figures anyway!

Fair to say from Dyno testing race engines and playing with cam timings, mostly 3 degrees or so is not significant. At 6 degrees yes things are changing but not as startling as you may think! This is not to say I don't degree cams in to the nearest degree as every little helps, but just bear this in mind when checking your timing.

Hope this helps

Nigel.

[blaat!]

Very helpful Nigel, thanks. The thing the manual doesn't specify is "Before Top Dead Center" or "After Bottom Dead Center", etc. but I guess that would be obvious to anyone that "should" be doing this type of thing...

Here are my results along with the workshop manual targets:
Intake open at 61° BTDC (target = 62°)
Intake closed at 79° ABDC (target = 76°)
exhaust open at 70° BBDC (target = 70°)
Exhaust closed at 48 ATDC (target = 48°)

I was super extra careful during assembly and it seems the numbers are good provided they are happening at the proper time (BTDC, etc.). Any chance you (or anyone) can confirm that they seem correct?

Much appreciated!
Jim

[LaceyDucati]

Looks perfect to me Jim, Happy days!

Nigel