quick 426 timing question..

hi all, please excuse the brevity.. Phone is currently getting rather oily posting this :smirk:

Doing the shims on my 426 and i'm looking at the timing.. Top dead mark aligns with piston top dead are per probing, inlet cam punch mark aligns with head but exhaust cam punch mark is higher than head by about half a tooth's height. If i move the sprocket one tooth anti-clockwise the punch mark is lower than the head line (and it looks like it's lower than higher if that makes sense).. Additionally there are 12 pins between the top two punches with the exhaust punch mark higher, and 13 with it lower.. Not sure how to time it- high or low? I have pictures of both sides if needed. Also note i'm keeping the front side of the chain tight as i time (i've seen tensioness pull an engine out of time, promise i'm not doing this!)

Could this bike have a wrong exhaust cam in? Thanks

If these are stock cams, the two sprockets will be identical. If the exhaust cam has a spring and flyweight on it, it's an auto decompression cam, and you need to find out whether it's an OEM 450 cam or an after market product like a HotCams unit.

It sounds as if the timing chain is stretched badly enough to throw your timing off by a half tooth, assuming both cams are OEM 426 parts.

heres what my wr426f timing looked like. the only difference i think between the stock cams between the yz426f and the wr426 is the placement off the punch marks on the cames. i think they both should have 13 pins inbetween the the two top marks on the came with stock cams.

DSCN8190.jpg

Here are the pics (click for bigger). Timing mark aligned on the flywheel:

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Looking at the timing marks (note, eye not level with head; i took a better pic)

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Level with the head (i came to realise that looking on a slight downward angle does distort the perspective somewhat)

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[Open Image] [Hosted by PhotoGalaxy.com]

Note only 12 pins?

And heres a shot from the other side of the engine, not that we can tell much from this side.. It's also slightly high

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[Open Image] [Hosted by PhotoGalaxy.com]

Does this look stretched? Any way I can tell? Can I measure a set length of it with a vernier caliper?

Thanks guys

You could measure a section of the chain, IF you had a spec for it. Don't know of one, though.

Your engine appears correctly timed. The E and I mark must be used as the primary reference. Write off the pin count as a variation due to your model year. The slight counterclockwise position of the marks is probably due to chain wear.

Thanks grey! I'll leave this thread up as a picture resource for anyone who needs it

2001 YZ426 (5JG)

if I am looking at the pic right, the exhaust cam mark to the intake cam mark there is only 12 pins. You are 1 tooth off on the exhaust. Should have 13 like the post before you.

I am assuming this is a YZ, not the WR. The exhaust looks like a WR cam

if I am looking at the pic right, the exhaust cam mark to the intake cam mark there is only 12 pins. You are 1 tooth off on the exhaust. Should have 13 like the post before you.

I am assuming this is a YZ, not the WR. The exhaust looks like a WR cam

Pin count between sprockets is not how cams are timed. The I and E marks are the definitive authority. Even though 13 is the usual normal count, moving either cam shown to achieve a count of 13 pins would end up with the actual timing mark badly misaligned.

As I said, chain stretch is likely to bear on this to some extent, but in the end, it's the actual timing marks, and not the countt between sprockets that matters.

http://www.thumpertalk.com/forum/showthread.php?p=7467845#post7467845

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