Yz426f low compression


10 replies to this topic
  • Cbogle7

Posted March 02, 2015 - 07:15 AM

#1

Hello I have a 426 I prob put 15 plus hours on this summer and I i started noticing that I could kick threw TDC with out decompression lever but it would still start right up on hot start after start turn hot start off and she run fine and plenty fast after riding it for a while after that it was getting harder and harder to start and now it has a little bit of compression but still not near what it should I have changed rings and gasket I was just wondering if the valves need reshimmed can that cause my compression to just slowly go away

  • FactoryJake

Posted March 02, 2015 - 07:56 AM

#2

Hello I have a 426 I prob put 15 plus hours on this summer and I i started noticing that I could kick threw TDC with out decompression lever but it would still start right up on hot start after start turn hot start off and she run fine and plenty fast after riding it for a while after that it was getting harder and harder to start and now it has a little bit of compression but still not near what it should I have changed rings and gasket I was just wondering if the valves need reshimmed can that cause my compression to just slowly go away

Sounds like your valves are out of spec. I would go re-shim them.



  • Cbogle7

Posted March 02, 2015 - 02:52 PM

#3

Thank you will do you know about how much a shop will charge

  • FactoryJake

Posted March 02, 2015 - 06:23 PM

#4

Thank you will do you know about how much a shop will charge

Well, it really does depend on what shop you bring it too. I would for one, watch a youtube video and look up how to do it, because they're fairly easy to do. But if you can't do them yourself, I would call around and ask for their price on re-shimming a bike. The shops around my area are 75 dollars per hour and will usually charge around 150 for re-shimming the valves. Just make sure if you do take it to a shop, they're not a bunch of idiots.


Edited by FreeRide250f, March 02, 2015 - 06:23 PM.


  • Cbogle7

Posted March 09, 2015 - 04:48 AM

#5

Thank you very much and well it's buying the reshim kit that cost quite a bit and I rather have some one do something like that for me then try it my self and end up with more money out of my pocket could I just take my head in and they reshim it

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  • FactoryJake

Posted March 09, 2015 - 06:56 AM

#6

Thank you very much and well it's buying the reshim kit that cost quite a bit and I rather have some one do something like that for me then try it my self and end up with more money out of my pocket could I just take my head in and they reshim it

Once you learn how to do it once it will save you a ton of money in the future. Just a thought. But I think you can just take the whole bike into the shop and they will fix it right up for you. If you can take the head off you can shim the bike to be honest. It is not really hard, just some simple math such as adding and subtracting and finding the current clearances of your bike with feeler gauges. A YouTube video can really help. But yeah, got a little off topic but you should just take the whole bike into the shop. 



  • Cbogle7

Posted March 15, 2015 - 04:52 AM

#7

Thanks im hard on time right now so I'm just taking my head in im a full time college student and work a part time job. That is almost full time so time is very limited to get around and this but I will look into doing it myself considering that's the type of family i come from but thanks the shop said be under 50 bucks to do it and get a valve job done

  • grayracer513

Posted March 15, 2015 - 09:06 AM

#8

If you take the head off the engine, the clearances can be set, but you or someone else would need to recheck them again once the head was torqued back down again, as they can shift slightly.  There is absolutely no reason to remove the head to set valve clearance. 



  • Pooley

Posted March 18, 2015 - 11:11 AM

#9

I don't know if you HAVE to buy the whole shim kit since they include sizes you will never, ever need.  Once you measure the clearances, you should know exactly what size shim to put back in.  This would not require an entire kit.  Check to see if you can buy just what you need, plus maybe 1 size smaller as well to allow for wear.  If it is more than a shim or 2 on the tight side, you may need to physically check the valve and head for unacceptable wear.


Edited by Pooley, March 18, 2015 - 11:13 AM.


  • Cbogle7

Posted March 20, 2015 - 08:50 AM

#10

So the shop is telling me I need to knew valves but they hold compression just fine with the cams are not in so can I just tell the shop to shim what inhale since I know my valves are holding compression

  • grayracer513

Posted March 20, 2015 - 09:31 AM

#11

Proof read your posts. Your phone's predictive typing is making you look bad.

 

It is very possible to have a titanium valve that seals OK under pressure but fails visual inspection.  The valve in the foreground below is in good, serviceable condition, the one in back is not.  Notice that the actual contact area of the valve face in front does not show a bright wear stripe around it.  If it does show that, even if there is no obvious detectable wear ledges, as can be seen in the background valve, the valve should not be reused.  This is because the bright band indicates that the nitride coating is at least very nearly gone, and if used, the valve will wear very rapidly from that point.  That's a hazard, to start with, and a simple waste of time and money.







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