Timing moves

Classic short-frame models

Re: Timing moves

Postby Ferrous_Head » Fri May 29, 2020 11:09 pm

Mo, the drive gear on the end of the cam won't spin. It's actually cut into the shaft.
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Re: Timing moves

Postby Ferrous_Head » Fri May 29, 2020 11:19 pm

How is the mag mounted ?

It should have the manual advance/retard setup. Is that still on there or have you gone to a "fixed" magneto ?
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Re: Timing moves

Postby Otis » Sat May 30, 2020 7:03 am

The last scenario is the only plausible one. I tried 3 different mags. I’ve been working on antique HDs for years, not saying I cannot make a mistake but not multiple times. Timing is fully advanced when setting timing. Points are set at .015. Seems like points generally start opening early after correctly setting timing. Maybe 30 degrees? Almost like it skips a tooth which would be 36 degrees. Going to open up the cam chest. I’ll let you know if I find something. Thanks
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Re: Timing moves

Postby Ferrous_Head » Sat May 30, 2020 10:10 am

I can't see a scenario where it skips a tooth. And if it did your valve timing would go south at the same time. Unless your talking about a tooth on the mag drive worm gear on the end of the cam. But if you had a broken tooth on there it would skip one tooth every revolution. The ignition timing would be so far out by the second revolution it wouldn't fire at all.

So, you are advancing the mag when doing the timing. That means you have slots in the mount that allow the mag to move. Is the timing getting retarded by 10 degrees ? Or advanced ?

If you are doing the timing by using the marks on the flywheels I suggest you try piston position indicator instead.

Because no matter what the flywheel marks say physical position of the piston will be accurate.
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Re: Timing moves

Postby Tim The Grim » Sat May 30, 2020 3:29 pm

Image

Some are keyed. Some not.

Maybe yours is rotating on the shaft.

Cam on right is KHK that I re-shafted and keyed as original.

Cam on left is OEM KR with no key slot on shaft
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Re: Timing moves

Postby Ferrous_Head » Sat May 30, 2020 7:41 pm

Well, the man told us he had a 66 XLCH. It would be extremely rare and unusual to find a set of shafted XLR cams in there. I would expect stock PB cams unless told the engine had been "Hot Rodded"
IIt might have Honda cams in there in that case.
The 66 had an advance/retard mechanism. I'm old and my memory isn't perfect but isn't there a second mark on the flywheel for timing at the retarded position ?

I always check to see that the timing mark I am going to use lines up with the correct piston location - 11/16ths BTDC.

So, I am still curious. Does the timing always change by a set amount in only one direction ? eg always 10 degrees retarded ?

Never advanced, never more or less ?
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Re: Timing moves

Postby Otis » Sat May 30, 2020 9:27 pm

The timing seems to get further advanced always but I’m guessing more like 30-40 degrees. I pulled the cam cover this evening and I don’t see a smoking gun but hadn’t got too deep into it. The drive gear is one piece with the cam and teeth look ok. The breather valve seems to be a little off. I had another 69 ch which someone assembled the gear case with the pump drive gear in flip flopped and the breather was the same as this. It ran but probably not to it’s full potential. I’ll do more investigation another day and keep you posted. Something is wrong and I’ve put it on my bucket list to figure it out. Thanks for any past or future help.
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Re: Timing moves

Postby Otis » Sat May 30, 2020 9:30 pm

Also is there a way to check BTDC without pulling the head? I’ve tried it with a dial indicator through the spark plug hole but could not get an accurate reading because of the angle.
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Re: Timing moves

Postby Ferrous_Head » Sun May 31, 2020 1:05 am

The breather valve seems to be a little off


Don't worry about small amounts. Most of them will not center exactly. It's irrelevant in a street engine. If it's a tooth out, then fix it.
Piston position indicators are accurate enough. You can use a pencil and get close enough. But the screw in dial indicators are much easier and more accurate. If your really keen you'll put a timing light on it afterwards anyway.
There is about 30 degrees of movement in the advance/retard system.
But normally, if the mounting nuts are too loose. the mag wants to go full advanced.

Something isn't adding up here.

If you have it fixed at 45 BTDC and your telling me it becomes 30 degrees too far advanced after one ride ......
The engine wouldn't be running as you pulled into your driveway. These things won't handle 75 degrees of advance.

How are you checking the timing after the ride ?
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Re: Timing moves

Postby thefrenchowl » Sun May 31, 2020 4:36 am

Once a long time ago, I set the timer 180 degrees out on my KK... ie 33 deg before TDC on the front cylinder exhaust stroke

Believe it or not, the engine ran in a fashion.

If you check again the timing on the compression stroke rather than the exhaust one as I did, you would find a 45 deg or so difference from normal timing...

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