Correct timing when reassembling the head/cam?


9 replies to this topic
  • SteveON

Posted April 03, 2008 - 07:23 AM

#1

I am about to start reassembling my NX650 (same engine as a XR650L) after taking off the head to remove a broken exhaust stud (very long frustrating experience). The head is all cleaned up and ready to go back on. My questions is how do I insure the cam is installed properly?
- From what I understand from reading the manual the piston should be at TDC with the marks on the flywheel lining up (looking through the observation hole on the left cover)?
- The cam sprocket has a line across it that should line up with the top of the head with the cam lobes facing down when installed properly?
- After that the cam tensioner can be installed?
- I bought a new stage one hotcam and I was reading about using some special grease when it's assembeled?
-How do I know if TDC is showing on the compression stroke or the exhaust stroke? Is there anything else I should lookout for?
Sorry for all the questions but I want to make sure I do it right the first time!
Thanks for all your help!
Steve

  • cleonard

Posted April 03, 2008 - 09:18 AM

#2

Until you put the cam in there is no comp or exh stroke. The cam defines that. Put it in with the lobes down. That makes it the comp. With the lobes down the cover goes on a lot easier. You don't have to fight the valve springs.

Use the "T" mark on the flywheel, not the "F" mark.

The grease is moly paste and is available at any Honda dealer. Good stuff for other places too, like the shock bearings. If you prime the oil pump and pour some oil in one of the valve adjustment covers it is not really needed. If you do use it, put the cheapest oil you can find in the engine. Then change it after about 5 minutes of run time. The moly in that grease is deadly to clutches.

After you have it all put together, turn the engine over a couple of times and check the alignment of everything. So far my record in only about 50/50 for getting it right the first time. It will not be exact in alignment. If you are one tooth off the alignment will be way off. On the order of 10 degrees.

Otherwise you got it right.

  • Motosprtman

Posted April 03, 2008 - 09:57 AM

#3

I just did my first "newer" model XR engine top end for a friend on a 82 XR250R, different than the old XL's in that all the cam stuff was moved from the left to the right side of the engine, yet the principles remain the same. Cam sprocket marks flush with the top of the head with the piston at TDC and cam lobes down. I always make sure the piston is at the topof the stroke when I install the cylinder, knowing that when I install the head, that step is taken care of, i.e. piston is at TDC and "T" is aligned. Then I install the cam chain tensioner and guide, slide the head on and then slip the cam through the sprocket and align the chain onto the cam for a TDC install and snap the sprocket up onto the shoulder of the cam. install one of the cam sprocket bolts rotate to installthe next one and then rotate again 360 to ensure that I have TDC and the T aligned with the sprocket marks flush with the head. Once you do it you will never forget and your fear of doing a top end is gone forever and you will wonder why you ever let HONDA do anything! (if you ever have)

  • creeky

Posted April 03, 2008 - 11:02 AM

#4

I shy away from moly paste on the cam lobes for the same reason that cleonard states, the moly is not clutch friendly. I have been using assembly lube that is specific for new camshafts, it is available at most auto parts stores.

  • Motosprtman

Posted April 03, 2008 - 12:10 PM

#5

I agree with Creeky and that is what I use too.

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  • BWB63

Posted April 03, 2008 - 02:22 PM

#6

I know this is for the XR650R but, the idea is there to make sure you have the timing you want.

http://www.scott-wor...engineering.htm

  • SteveON

Posted April 03, 2008 - 03:40 PM

#7

Thanks for all the help! I got the engine all back together and she fired right up! I only started her for a couple of seconds to make sure everything was Ok before I assemble the rest of the bike. Hopefully tomorrow I'll finish getting it together and run it @ 3,000 rpm for a little to break in the cam then change the oil out, recheck the valve lash and be ready to enjoy some new power! I also did Dave's mod on the carb, that was actually very simple. BTW I called hotcams about the lube and they said not to use a moly base assembly lube but a petrol based one.
Thanks again!
Steve

  • motox-quadracer42

Posted April 06, 2008 - 06:25 PM

#8

do you still have the old cam and is it still in good condition? if so how much would you sell it for?

  • SteveON

Posted April 07, 2008 - 09:05 AM

#9

The bike is finally all back together and running good. Last thing l need to do is install the smog blockloff plates but the bolts are really stuck and I don't want to break anymore off and go through the whole mess of disassembling and drill out old bolts/studs ever again. I was thinking about maybe just cutting the chrome pipe off a little shorter and thread a bolt in there?

I"m going to keep the old cam for a little bit to make sure the new one is what I really want. After I make that decision I'll IM you if I want to sell it.
thanks,
Steve

  • creeky

Posted April 07, 2008 - 04:09 PM

#10

When starting after assembly, it's a good idea to loosen the banjo fitting on the oil pipe going to the head while the engine is running to make sure that the oil pump has not lost prime. If you have a good oil flow out of the fitting, no problem.





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