No Compression


15 replies to this topic
  • Lok47

Posted December 06, 2005 - 05:57 PM

#1

I repalced all the gaskets on the top end because i had some leaks and now my WR doesn't have any compression at all (i.e. no hard spot). So, it just kicks over and over. I've checked the decompression valve and lever and it doesn't seem to be stuck or anything. The timing is okay I think (I followed the manual to the T). Does anyone have any ideas/tips/tricks?

I've got trackdays this weekend and I'm hoping to get this going asap, so any and all help is greatly appreciated. Thanks!

  • new2blu

Posted December 06, 2005 - 06:23 PM

#2

I guess you replaced the head and th base gasket? You removed both camshafts? If you removed both camshafts re-check the positioning of them. Not sure on your bike but on my YZ450 there are punchmarks on both camshaft gears. The exhaust "front" cam punchmark faces the front of the bike with the mark even with the top of the head. The intake"rear" cam is just like the front except that the mark faces the rear of the bike. These references are when the engine is at TDC. Also at TDC the front cam lobe should face the front and the rear cam should face the rear of the bike.

Hope this is helpful.

  • ISBB

Posted December 06, 2005 - 07:06 PM

#3

lets not overlook the simple things... you did put the sparkplug back in right

  • Lok47

Posted December 06, 2005 - 08:27 PM

#4

yep, sparkplug is in.

At TDC front cams are facing the front and rear cams are facing the back. When I adjusted the timing, I lined up the "I". I'm supposed to use the I that is next to the H right?

  • tshe1

Posted December 06, 2005 - 10:30 PM

#5

yep, sparkplug is in.

At TDC front cams are facing the front and rear cams are facing the back. When I adjusted the timing, I lined up the "I". I'm supposed to use the I that is next to the H right?

yes you right.
it is obvious that you have compression leak.
you have just 7 ports that you can loose the compression: 3 intake valve, 2 exhaust valve, piston,spark plug.
if the spark plug is tighten good and the piston is good in it's position then your leak is from one of the valves.
i had this problem and found out that one of the valve was held press because of distorted bore of the valve lifter.
(check that the "E" mark on both sprockets are in the left side with the timing.)
another possibility is that the valve are not seal good, their is no enough information about what have you done to the head(?)

  • Indy_WR450

Posted December 07, 2005 - 03:45 AM

#6

Valve clearances that are too tight can cause a leak. Check all your clearances and make sure you have them on spec. :applause:

  • StreetbikePimp

Posted December 07, 2005 - 06:33 AM

#7

Did you torque your cam caps too tight?

  • Lok47

Posted December 07, 2005 - 08:34 AM

#8

So, i removed the cams last night and lef the plug in. I had my roommate hold the timing chain so it wouldn't bind and pushed on the kick starter. It felt like it held compression. I'm assuming now it has to be a timing problem, like most of you have said. Is it possible I had the cams 180* off? Does it i matter which part of TDC the motor is at?

After trying to crank it over, I noticed the cams are backwards, but the thing is still at tdc. So I used a ratchet to turn the crankshaft over. When I got the cams to line up "E - I - E - I" it was also with the I mark within the rotor viewing hole. So with the I on the rotor at TDC, I get "E - I - E - I" and also "I - E - I - E". I'm pretty confused with all this since I've been focusing on the timing and I come to find I'm still screwing it up

I doubt the cam caps are too tight because I still see them moving smoothly with the valve cover off.

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  • jchantzWR400F

Posted December 07, 2005 - 12:01 PM

#9

Here's a shortcut to a thread about this

http://www.thumperta...97&parentpage=8

  • StreetbikePimp

Posted December 07, 2005 - 03:11 PM

#10

Does it i matter which part of TDC the motor is at?



YES!!!

There is only 1 TDC for your motor. TDC is when the piston is at the very top of the cyclinder after the INTAKE stroke. (not the EXHAUST stroke)

When you're lining up your timing marks, you should only be looking to see if they are all lined up after the INTAKE cam has open the INTAKE valves.

  • TD-3

Posted December 07, 2005 - 04:51 PM

#11

YES!!!



Really?

Doesn't the motor fire everytime time the flywheel triggers it? If so it's impossible to be 180 out. :applause:

  • tshe1

Posted December 08, 2005 - 02:13 AM

#12

So, i removed the cams last night and lef the plug in. I had my roommate hold the timing chain so it wouldn't bind and pushed on the kick starter. It felt like it held compression. I'm assuming now it has to be a timing problem, like most of you have said. Is it possible I had the cams 180* off? Does it i matter which part of TDC the motor is at?

After trying to crank it over, I noticed the cams are backwards, but the thing is still at tdc. So I used a ratchet to turn the crankshaft over. When I got the cams to line up "E - I - E - I" it was also with the I mark within the rotor viewing hole. So with the I on the rotor at TDC, I get "E - I - E - I" and also "I - E - I - E". I'm pretty confused with all this since I've been focusing on the timing and I come to find I'm still screwing it up

I doubt the cam caps are too tight because I still see them moving smoothly with the valve cover off.

calm don, it's very simple:
1. turn the crank to TDC withe the "I" mark line up (without the cams install).
2. after you will be at TDC install both cams: first exhaust then intake, withe both "E" mark to their left (like in the manual) without turning the crank!!! (be carfull not to drop the cam clip to the crank-appends to me twice!!)
3.tighten the cams (after you ara sure with the timing), with crisscross pattern to specified torque.
4. measure the valve clearance.
good luck!

  • R_Little

Posted December 08, 2005 - 10:36 AM

#13

Doesn't the motor fire everytime time the flywheel triggers it? If so it's impossible to be 180 out.



I believe the ign fires everytime the flywheel turns past the trigger....Since it is a 4 stroke it will "waste" a spark every other revolution.

The CDI will not know whether it is at the compression or exhaust stroke. You would not be able to be 180 out.

If the valves are lined up properly at the "I" mark and the valves ae adjusted correctly then it should fire up....unless you have a huge hole in the piston or no gaskets or something.

  • RichBaker

Posted December 08, 2005 - 12:42 PM

#14

TDC is TDC is TDC. Until you put cams in it doesn't matter, as long as the piston/crank is at the top of it's stroke. Once the cams are in and properly timed you'll have 2 TDCs. TDC compression and TDC exhaust...

  • HotCams

Posted December 08, 2005 - 02:06 PM

#15

TDC is TDC is TDC. Until you put cams in it doesn't matter, as long as the piston/crank is at the top of it's stroke. Once the cams are in and properly timed you'll have 2 TDCs. TDC compression and TDC exhaust...


Exactly! It is the cams that determine which stroke it is on. So you cant install the cams 180 out.

  • HamBonE_23

Posted December 12, 2005 - 01:53 PM

#16

If you've verified that you're 100% TDC then there is one other thing to look at.
When you are tightening down the cams see if any of the bolts are harder to tighten than the others. I had this problem with my bike after redoing the top end. I accidentally had the spacer for the valve move and it wasn't recessing, thus it was have a compression leak. When I kicked it you could feel there was no compression and like you I took it apart many times trying to figure it out.
Hope this helps.




 
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