yz 426 extended timing chain? cylinder riser plate??


11 replies to this topic
  • Devilman0686

Posted August 09, 2011 - 01:14 PM

#1

i bought a yz 426 and from what i am told it has a gt thunder 460cc stroker kit on it, well when i went to change the timing chain and the cams i was in for a surprise and stupid me i threw out the old stuff and cannot find it. the problem i come across is the stock timing chain is too short, and reason being is there is a 1/4 inch riser plate that goes between my bottom casings and my cylinder (jug). can anybody help me find a longer timing chain? everyone i have talk to has never heard of this riser befor or a longer timing chain. HELP PLEASE!!!

  • William1

Posted August 09, 2011 - 03:12 PM

#2

The chain will fit. A new chan in some cases cause the cams to literaly 'snap in'. If the flywheel is off and the lower chain guide is unbolted, that can give you a little extra play to work with.
A spacer is common with some strokers to retain a piston with more than one ring.

  • grayracer513

Posted August 09, 2011 - 03:42 PM

#3

i bought a yz 426 and from what i am told it has a gt thunder 460cc stroker kit on it, well when i went to change the timing chain and the cams i was in for a surprise and stupid me i threw out the old stuff and cannot find it. the problem i come across is the stock timing chain is too short, and reason being is there is a 1/4 inch riser plate that goes between my bottom casings and my cylinder (jug). can anybody help me find a longer timing chain? everyone i have talk to has never heard of this riser befor or a longer timing chain. HELP PLEASE!!!

The spacer should be closer to 2.4mm (3/32"), as that would be half the required difference in stroke to increase the engine to 460cc. That, you should be able to run a stock length chain onto, but you should realize that even with the stock stroke, you cannot assemble the chain onto the cams while they sit in their saddles.

Normally, the best procedure is to position the exhaust cam with the chain on it first, then place the intake cam in the center of the head position the chain over it, and then tilt and roll the cam into position and seat it.

If you get the timing aligned on the exhaust, a tip that helps you guess right on the intake more often is to position the chain on the intake so that there are 13 pins of chain between the two 12:00 marks on the cams. You still have to check the timing with the I and the E marks against TDC, but you'll usually hit it the first time by doing it that way.

  • yz454

Posted August 09, 2011 - 06:48 PM

#4

Count the pins on both chains. If the same your good ,if not I put together my own chains because mine is spacered more than .500.

  • Devilman0686

Posted August 10, 2011 - 09:06 AM

#5

I still don't thing it will work but i am willing to give it a try. thank you for your help so far and i will keep you guys posted on my results. i got a we-mail from a guy at gt thunder and he said he never uses a riser plate or hot rod cam or a longer timing chain so somewhere along the line some information was wrong.

  • Devilman0686

Posted August 11, 2011 - 08:11 AM

#6

Wel li tried to snap the cams in lastnight and their was not even the slightest chance that i would even get the chain onto my exhaust cam, is there a tool i can buy to make my chain longer, this is not the route i want to go but might just have to. Input anybody?

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  • GCannon

Posted August 11, 2011 - 08:30 AM

#7

Call these guy's maybe they can help you:
http://www.faliconcranks.com/bbk.html

  • yz454

Posted August 11, 2011 - 08:24 PM

#8

Do you buy any chance have the cam tensioner in ,if you do take it out and put the cams in.

  • pscook

Posted August 12, 2011 - 08:07 PM

#9

I have run into this one problem (of my own causing) every time that I removed the cam chain: When installing the forward chain guide, the chain droops around the crank sprocket. All of a sudden, the chain is one link too short. Could it be? I remove the flywheel, and there it is, the chain is not properly seated on the crank sprocket. Check that first, then follow Gray's procedure. Three (consecutive) times. You would think that I should have learned by now.

  • grayracer513

Posted August 13, 2011 - 07:58 AM

#10

I have run into this one problem (of my own causing) every time that I removed the cam chain: When installing the forward chain guide, the chain droops around the crank sprocket. All of a sudden, the chain is one link too short. Could it be? I remove the flywheel, and there it is, the chain is not properly seated on the crank sprocket.

That is "not supposed to happen", because the guides are supposed to fit close enough to keep the chain in place, but it does. Definitely worth checking for.

  • Devilman0686

Posted August 18, 2011 - 12:10 PM

#11

The chain tensioner is not in, the chain is not binding at the crank, no idea whats going on here. the only things i can see it being is the chain is just not long enough....ready to just put it back to stock and cut my losses. Thank you all for you help and input but i am getting nowhere ,perhaps i will put it right apart and see if their is a marking on the crank that may help me.or see if i can ditch that riser plate.

  • grayracer513

Posted August 18, 2011 - 01:28 PM

#12

The riser plate is there to accommodate the increased stroke, if any. It needs to be half the amount the stroke was increased by. If the stroke increase was 4mm, the piston will go 2mm farther down than it did when stock, and 2mm farther up, thus requiring a 2mm taller cylinder, or a 2mm shorter rod, or a piston with the wrist pin bore moved 2mm closer to the crown.

The first thing to do would be to pull the head and measure the actual stroke. the stock 426 has a 60.1mm stroke (2.37"). As built stock, the piston will come right to the top of the bore and be nearly flush with the cylinder deck. This will tell you if the plate was incorrectly made, which is something I have seen done. One can erroneously decide he needs a 4mm plate for a 4mm stroker, when he only needs half that.





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