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2013 Suzukior RM-Z250 timing chain to taught for install

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Posted (edited)

Hello, hope i'm posting this properly!

So my first 4 stroke rebuild was going well, so i thought! I'm trying (hard) to put my sons bike (2013 rmz 250) back together after a top end and valve service. I am having a difficult time placing the timing chain over the camshafts. Sounds silly, I know! The tensioner is removed, the engine is at top dead center on compression stroke. The chain guide appears to be installed correct and the chain goes over the exhaust cam fairly easy while pulling the chain taut with no slack down to the crank or under the crank sprocket (the video appears as if i'm allowing slack to drop to the left below the sprocket but i'm not, the guide is pressing with tension against the chain & the bottom teeth of that sprocket & holding the tension from dropping there). The marks are at 12 o'clock and 9 for the left cam and 12 & 3 for the right. None of that should really matter for slack though, the book calls for 13 pins between the top marks which i can count but I just can't loop it over the intake cam. Now maybe it's a simple mistake, and hopefully i'm missing something simple.  Again my first 4T rebuild but I have tried to pay attention to detail and do things proper. I do have a manual & have followed it to a tee! For $100 its pretty vague on the subject, it just says follow the reverse order to assemble. Someone recommended I start the chain on the exhaust cam and then turn the crank to ride it up over the teeth like we all did to our bicycles as kids! The manual does not say this and it seems I would lose TDC if I did that. Is that a proper procedure? I would appreciate any tips on what I'm missing. Here are some pics at tear down and my video plea for help! Thanks in advance!

 

 

 

 

Edited by bosox5150
proper info

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Posted (edited)

I haven't watched the whole video but the first thing that comes to mind when I see you handling the chain

is that it wasn't kept under tension the whole time you had the engine apart (zip tied to the frame)

and by hanging loose it fell out of engagement with lower timing gear on the crankshaft.

 

Loosen it and let some slack drop into the bottom end before pulling it taut again,

moving the flywheel a bit to confirm the engagement with the gear.

Edited by mlatour

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Thanks for the reply and suggestion mlatour. I did check that and I did keep the chain zip tied and secure but no I did not keep it taut when doing so. I did however pull the cam chain guide out and look down to see if any links had jumped or bunched up under the crank shaft sprocket. I did then create slack & pull it tight like you said. In the video I have the chain over the left exhaust cam shaft with all tension pulled tight to that left cam sprocket, It could not slip back loose that direction which Is why I was not overly concerned with tension in that direction. Good point though and I appreciate the advice & effort.

I also realized that the marks being about 45 degree out of rotation was correct if I had disassembled at TDC on the wrong stroke. So that apparently is not an abnormality as I figured, it was proper for the current rotation.

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Posted (edited)

Watching the video a bit another thing comes to mind, while I'm not familiar with Suzuki, if it's anything like my CRF engine

even with no tensioner there is not enough slack in the chain to simply draw it over the cam gear(s) when installed.

Meaning the cams require to be lifted/angled so the chain slips on their gears first before being set down onto the cylinder head.

Edited by mlatour

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Posted (edited)

That is how I had to take it out, maybe I'm just over thinking it from watching other videos. Most everyone else seemed to have the slack to just loop it over. The CRF is a uni cam though so it's much easier to hold an angle & loop the chain while keeping everything in alignment. That's tough to do with 2 cams & only 2 hands! Guess I will need to get my son up & off his games & actually lend a hand with bike maintenance! Lol. Thanks again, I will try that way after work.

Edited by bosox5150
spell check
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Posted (edited)

So I got it, the old bicycle chain trick did it. 'I will leave this up for anyone with a similar issue, I hate when a post doesn't reveal the fix! I just started the chain on the intake sprocket (after it was pulled taut over the exhaust cam) and then turned the motor over slightly to work it on the rest of the right cam. The manual doesn't say to do it but it worked fine, there just wasn't enough slack otherwise. I was worried about losing TDC but it was clear after trying that as long as you align the 13th pin or whatever your pin count is with the top mark as you start to turn it will all stay align. It only took a 1/4 sprocket turn to get it, just reverse the crank spin to put it back TDC & check everything. Haven't fired it up yet but the motor and electrical are complete & I'm hopeful! I will finish the chassis & body work tomorrow after work, it's near midnight & 6am comes fast! Oh and my long of subject mention of the upside down marks in my video when I disassembled was do to TDC on the wrong stroke. I read a lot of different opinions if stroke was important, it absolutely is. A good trick is to use a leak down or compression tester hose & thread it in the cylinder with a balloon, latex glove or a rubber (magnum) zip tied on the end, turn the crank over slowly & when it starts to inflate your on the compression stroke! Pull the hose off before the stroke finishes & drop in your straw to find TDC! Straws are better than metal on metal! Hope this helps someone down the road!

Edited by bosox5150

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