2013 surging and bucking Again

Feel free to look up the previous posts:

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Pete Roper said that it's a roll of the dice to get a good cam sensor. The one I got from MG worked for a while/several rides but the same failure reappeared on a run through the mountains today on an 82 degree F/ 28 C day.

I will give the dice another roll...

This is an irritating one isn't it? It might be worth plumbing in an LED to the main ecu feed to see if power is dropping out completely. Does the headlight flicker when this occurs? Have you checked the depth of the phase sensor?

Pete Roper wrote:

This is an irritating one isn't it? It might be worth plumbing in an LED to the main ecu feed to see if power is dropping out completely.

Wow, scary thought.

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Does the headlight flicker when this occurs?

That I can test!

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Have you checked the depth of the phase sensor?

Interesting, might the sensor be going out of spec due to expansion/heat? How would I check the depth?

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Lots of stuff is scary but really the CARC series bikes are pretty reliable apart from the *Known Suspects* and really pretty simple. You can work it out. For a man of your abilities it shouldn't take long.

You can do it!

For step one I will use the VISA wrench and get one more sensor from MG Cycle. Now, about that sensor depth, how is that measured again? I have a metal plate and two screws...

Dial caliper end down the hole to phonic wheel tooth, subtract length of sensor is the number and you can get shims to make it right.    Book shows if you don't have a clue.

You can do it!!

GuzziSteve wrote:

Dial caliper end down the hole to phonic wheel tooth, subtract length of sensor is the number and you can get shims to make it right.    Book shows if you don't have a clue.

You can do it!!

Aha, When I removed the original sensor I didn't see any shims. The book is a little opaque on testing the sensor for failure.

(1) Is there a simple test I can do with a multimeter?

(2) After measuring for the air gap what do the shims look like? Same shape as the securing plate?

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O.K. upon further review what I thought was a single plate was a plate with two shims. That's actually better because my theory is that the air gap is too big and bad things happen once the engine gets hot. Shims pictured below. My rough measurement puts the air gap at 1.2 MM with both shims, .8 MM with the thin shim removed.

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When I worked in the jet shop, PW4000’s, we would put a little bees wax on the speed sensor, install it without shims, rotate the engine by hand a few degrees, remove the sensor, cut the wax through the scrubbed portion and measure the thickness of the wax then calculate the shim stack. If the wax fell off it was not a big deal, a little bees wax isn’t going to kill the engine. No dial caliper, depth micrometer etc, etc, just matched up a stack of feeler gauges. Basic math skills, not a super high precision operation.

Of course the wax was produced by industrial grade bees.

ratso88 wrote:

Of course the wax was produced by industrial grade bees.

I was thinking along the same lines, but the wax idea did not occur to me. Excellent suggestion.

Following up on ratso's wax story I used silver sharpie on the black plastic of the sensor, Installed it and spun the engine by hand. The sharpie was undisturbed so I fired up the bike and went for a 30 minute ride. The bike was very smooth and ran and idled perfectly. Tomorrow, a longer ride to see if the probem is really gone.

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Is there a prescribed shim thickness for this item? Just curious if I take off my existing sensor, which I've never done and let's say it has 1 shim...how do I know with certainty that 1 shim is the right thickness to install on the new sensor? What if that 1 shim was wrong all along?

No, the whole point of the shims is to be able to compensate for manufacturing variances of both sensor and the case it goes in to. If it works it is basically within its serviceable range. If it is at the very outer end of its sensitivity then as it ages and gets heat effected it may begin to deliver an inaccurate or inadequate signal which will then cause the spark and fuel delivery to break down.

Normally when the phase sensor goes it's sudden and permanent. The engine just dies. On rarer occasions the failure may only manifest as the engine, and therefore the sensor, heats up. If the sensor has been working and just dies then it can be assumed that its depth was correct, or close enough. In that case checking the depth of the new sensor is simple. Just put them up against each other with the tip resting on the other one's mounting flange. In my experience they are all pretty accurately made and their depth is as close to identical as makes no odds. If that is the case just use the same shim/s with the new one as the old one. If there is a length discrepancy? Compensate by adding or removing shim to ensure the depth remains the same.

Ideally to measure the air gap *Correctly* you should open the timing chest and measure it with a feeler gauge. Needless to say nobody does this because it's a king sized pain in the arse and a huge waste of time and effort. We use Steve's method of a vernier down the 'ole onto a tooth on the phonic wheel but the beeswax idea is clever and perfectly acceptable as well.

Thanks Pete…splendid insight! Much appreciated!

Applause for the group experts! 45 hot miles today without a stumble.