I just rebuilt a vintage Yamaha XS650 motor but was having a problem with plug fouling problem. I did an in Cylinder compression test and it appeared that I had a camshaft timing problem. I was positive it was installed correctly and as it turned out it was. After doing some research I discovered that the spec in the service manual for valve clearance was wrong. The interesting thing was I was only out by .003" loose. Apparently this cam has very slow opening and closing ramps as you can see in the change in the before and after wave forms. How da thought...lovin the Pico.

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Excellent!  [smiley=rockon.gif]

Good for you and thanks for posting it!

James H wrote on Dec 10^th, 2016 at 9:14am:

out by .003" loose. Apparently this cam has very slow opening and closing ramps as you can see in the change in the before and after wave forms. How da thought...lovin the Pico

James, interesting, wonder how many people struggled with issues on a lot of motors never being able to pin it down. Liked the XS650, just make sure all your fillings are glued in tight, @ least as I remembered it, but like Spence maybe our rememberer is not as good as it used to be, ;D :D

Yeah,............the Pico can answer a lot of questions, you came to the right place.  Would like to see more posts in the MC section as most the shops I go to have no idea what that thingy is in the exhaust pipe, like an 02 sensor, not joking here.

The .003 making the difference is interesting in  itself as most of us would rather have a valve a little loose than tight.

James H wrote on Dec 10^th, 2016 at 9:14am:

I did an in Cylinder compression test and it appeared that I had a camshaft timing problem.

Morning James do you have a saved psdata file of the bad running engine at 2000 rpm also the Fixed psdata file you show here.

The compression wave distorts a lot on low compression car engines over 2000 rpm, so I am interested in comparing these motor cycle engines.

Your fixed image shows very good if thats 2000 rpm. 8-)

StitchB wrote on Dec 11^th, 2016 at 6:10am:

James H wrote on Dec 10th, 2016 at 9:14am: out by .003" loose. Apparently this cam has very slow opening and closing ramps as you can see in the change in the before and after wave forms. How da thought...lovin the Pico James, interesting, wonder how many people struggled with issues on a lot of motors never being able to pin it down. Liked the XS650, just make sure all your fillings are glued in tight, @ least as I remembered it, but like Spence maybe our rememberer is not as good as it used to be, ;D :D

Ok Larry I'll bite... What are you saying here?   [smiley=scared0016.gif]


StitchB wrote on Dec 11^th, 2016 at 6:10am:

Yeah,............the Pico can answer a lot of questions, you came to the right place.  Would like to see more posts in the MC section as most the shops I go to have no idea what that thingy is in the exhaust pipe, like an 02 sensor, not joking here. The .003 making the difference is interesting in  itself as most of us would rather have a valve a little loose than tight.

I would agree. Most of the high reving engines I have had valve clearance issues with liked looser valves.

I partially agree with Mick and would like to compare rpm with equal rpm. The higher rpm distortion jury is still out.  8-)

Mick, there you are. The bad one is at 2000 rpm as the engine did not want to run well enough at idle. The good one is at 1000 rpm.

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James H wrote on Dec 11^th, 2016 at 2:58pm:

Mick, there you are. The bad one is at 2000 rpm as the engine did not want to run well enough at idle. The good one is at 1000 rpm.

It is always best to compare at equal  RPMs So all you have to do for us is increase the fixed engine to 2000rpm I believe, ;)

So how many degrees before/after TDC does the intake valve open and how many degrees before/after TDC does the exhaust close?

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