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Author Topic: Need some top end info  (Read 281 times)

Offline kevinpd1987

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Need some top end info
« on: February 18, 2018, 09:10:52 PM »
Ok so I had a hard starting issue so I decided to go and check valve clearances and had 0 on intake and .002 on the exhaust and when I took the cams off to check the shin sizes my cams popped up kinda making me think that my valves are stretched or the seats are punched in. my shims are already as small as they come .... so a few questions
- what is the length of stock valves
-does the stock piston have two small divets for the intake valves (so they don’t contact) if not could this have happened to my piston because the timing chain is stretched?
-if I find that the valves are ok is there a way to replace the seats ?

Any information on these questions or a point in the right direction would be much appreciated

And if anyone has a head laying around that they know is good I will buy it

Offline kevinpd1987

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Re: Need some top end info
« Reply #1 on: February 18, 2018, 09:48:16 PM »
they are clean compared to the rest of the piston so I’m going to safely assume that the valves are contacting the piston


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Offline Dirk1616

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Re: Need some top end info
« Reply #2 on: February 19, 2018, 06:20:24 AM »
Didn't you just ask about this problem a little while back? Haha, but anyways.
Usually when it becomes hard to start these, it's because the valves aren't holding compression well. The top of the piston is supposed to be flat with no divots, so those marks you see are from the valves. I've see worse, and it sounds like you can still start it, so I don't think they would be bent. Perhaps the reason you valves are smacking the piston could be from your timing chain tensioner going bad, which allows more slack on the timing chain which would throw the timing off just a tad. I'm not sure what year you have, but I know that just about all of the earlier model years tensioners do go bad, they redesigned them with a different part number and it works much better, so get a new one.

The seats wear into the valves and put a radius onto the valves which causes you to lose clearance between the valve and the cam. The intake valves tend to wear a little more than the exhaust valves do. I'd take out one of your intake valves and see what it looks like. If it's flat, you're good to go. If it's got a radius on it, then it'd be best to get new intake valves, or regrind if they aren't too bad. Check your exhaust valves too, but those should be in better shape. As far as the seats go, if there's a radius on the valve, there's a radius on the seat. Seats you can have reground, or you can buy new ones. There are kits to take them out and put in new ones I believe, sounds like a pain though, I just have them reground. An engine shop or powersports place should have the stuff to regrind your seats fairly easy. If you don't have your seats reground flat, any new valves you get won't last as long as they should and you'll be in the same spot you're in now. And don't let someone tell you that your seats are flat enough that they don't need reground! If you have a radius on your valve, there is a radius on the seat! Get them flat again.
I didn't get mine reground the first time, but I had got new valves, and put them in with the correct clearance. After 2 days of riding, I lost all my clearance and the brand new valves I got were junk because the seats put a radius in them!! >:( So I say again, make sure your seats are flat.

As for shims, any powersports place should have a box set that they use. You may be able to buy the size shim you need. You can buy a set online, but beware, they can be expensive. If you know of anyone who works in a Machining shop with a surface grinder, they can take off as little as .001 or less on shims, so if you want to use your own shims, just tell them what thickness you want it to have or tell them how much you need taken off and they'll make it to whatever you want. If you don't know what size shim you want or need or don't want to get any new shims, you can grind a little of the top of the valve with a little die grinder. This will take some time to take a little off at a time and to check it every time you grind, but it'd be like changing shims, I've done it, and there's no problem if you do it right. Make sure the tops of the valve stems are as flat a possible. What I do to make sure they rest flat with the buckets is color the tops of the valve stem with a Red Sharpie, sit the bucket in place, spin it around a little, take it back out and see where the Red came off of the top of the valve. That will tell your where the high spots are and where it needs to be flatter. Checking your clearances should be the last thing you do, shoot for somewhere between .004-.006 clearance. I would try for .006 and wouldn't want to go below .004, otherwise once your valves start to wear again, that clearance will get smaller. If you start bigger, it'll save you a little more time between reshiming.

The better job you do now, the more time you'll save yourself before you are doing it again.
2003 DS Baja         Riding at Bundy Hill and Silver Lake
Big Gun CDI, 11.5 JE Piston, Port/Polish, OMR Carb Mods,
Custom Mod End Cap, UNI Filter, More To Come?

Offline kevinpd1987

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Re: Need some top end info
« Reply #3 on: February 19, 2018, 09:25:01 AM »
Thanks for the reply ! Well I did some inspecting of the valve’s and seats and both have what I think your talking about “radius” so with that being the case ..and me wanting to fix it once and not have to do it again down the road  I’m going to look into new valves and seats ... and the tensioner was bad I pulled it out and it fell apart .. so I will get a new one and a timing chain while I’m in the motor already .. does the left side timing  chain guide play a big role in chain tension as much  as the right side because my left side is wore out bad and the tensioner side seems fine


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Offline Dirk1616

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Re: Need some top end info
« Reply #4 on: February 19, 2018, 03:09:49 PM »
If there is any wear on the timing chain guide, that'll allow more room for the timing chain to move, which may not be a good thing. You want that chain to be taught and not have slack. So if possible, it would be best to replace any worn parts that could create a problem.

Here is the updated Timing Chain Tensioner:
http://www.2wheelpros.com/oem-parts/can-am-chain-tensioner-415129408-part.html

Here is the Timing Chain Guide (for the side that doesn't have the tensioner):
http://www.2wheelpros.com/oem-parts/can-am-chain-guide-420236230-part.html

I find that 2wheelpros always has OEM Parts a lot cheaper than everyone else, and free shipping over $100 bucks! Just takes a few extra days to ship.
2003 DS Baja         Riding at Bundy Hill and Silver Lake
Big Gun CDI, 11.5 JE Piston, Port/Polish, OMR Carb Mods,
Custom Mod End Cap, UNI Filter, More To Come?

 

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