installed new top end and bike wont start


15 replies to this topic
  • Dremitchellyamaha

Posted October 18, 2011 - 07:10 AM

#1

I have a 2001 yamaha yzf426 that ran hot so I cracked a cylinder so I bought a top end(cylinder,piston, cylinder head) and installed it, cleaned carb flushed oil out and bike still won't start all I got was one loud backfire. I have checked for spark and its got spark, verified camshaft timing to crankshaft timing. And I'm going to check valve lash and leakdown test today. Any help would be greatly appreciated because I'm trying to ride by the weekend. Before I get stationed in ga.

Edited by Dremitchellyamaha, October 18, 2011 - 07:33 AM.


  • Schpenxel

Posted October 18, 2011 - 08:46 AM

#2

check the valves

check the valves

check the valves

  • elcubeo

Posted October 18, 2011 - 08:51 AM

#3

lol yeah i agree, check the valve clearance. If they are too tight, you are getting too much effective overlap thus reducing your starting compression / efficiency. Also double triple check the cams are not phased incorrectly to the crank or each other. I screwed up once like that, the bike would fire if you bump started it, but not if you kicked it. It ran like crap down low and ran like crazy up high. Turned out we had the exhaust cam phased a tooth retarded.

  • Dremitchellyamaha

Posted October 18, 2011 - 09:43 AM

#4

Thanks for the input. Im going to check valves today.

  • Dremitchellyamaha

Posted October 18, 2011 - 02:20 PM

#5

I checked the valves and the exhaust valves were too tight, got them in spec. And it started on the first kick.

  • Schpenxel

Posted October 18, 2011 - 02:27 PM

#6

Good to hear!

  • elcubeo

Posted October 18, 2011 - 02:38 PM

#7

Awesome dude!!! Glad to hear! :thumbsup:

  • Dremitchellyamaha

Posted November 04, 2011 - 10:03 AM

#8

Ok guys here's the deal I rode the bike for about an hour and I parked it. When I tried to start it shown it wouldn't start. I pulled the plug and it was wet with coolant. I have a total of 3 cylinder heads and 2 cylinders so far none has worked. I checked two of the cylinder heads and they were warped so I have them being repaired at the machine shop at my school. What do you guys think the problem is?

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  • grayracer513

Posted November 04, 2011 - 12:26 PM

#9

Make, model, year?

  • sacfelix

Posted November 04, 2011 - 12:59 PM

#10

01 yz426

  • grayracer513

Posted November 04, 2011 - 01:19 PM

#11

01 yz426


:busted: :busted:

Anyway, now that I'm awake, how did you go about torquing the head bolts?

  • Dremitchellyamaha

Posted November 04, 2011 - 02:15 PM

#12

It's a 426 but I have a 400 motor with the 426 connecting rid and the 426 cylinder and cylinder head

  • Dremitchellyamaha

Posted November 04, 2011 - 02:25 PM

#13

I torqued the cylinder head bolts to 32 ft-lb

  • grayracer513

Posted November 04, 2011 - 02:31 PM

#14

In steps and in sequence, or all the way to 32 in a single step?

  • Dremitchellyamaha

Posted November 04, 2011 - 02:39 PM

#15

However the manual said nothing about putting lube on the bolts but I used the same torque method on my yz400f and it runs good

  • Dremitchellyamaha

Posted November 04, 2011 - 02:40 PM

#16

I torqued it in two steps





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