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 Post subject: tt 500 timing problems
PostPosted: Tue Jan 15, 2008 7:50 am 
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Joined: Thu Feb 09, 2006 6:10 pm
Posts: 51
HEllo,

Need some help, I just put a new piston and rings in my TT500, ( my first four stroke build) and when going back together with itI followed the manual, i aligned the T mark on the gear on the rightside of the engine, flywheel T also aligned, installed cylinder, piston, head, and then camshaft, book says to have the camshaft gear pin in the 12 oclock osition, did that, installed cam gear, book says index mark on cam gear will align with top of head sealing surface which it did, installed rocker box, checked valves, .0003 on intake, ,005 on exhaust, checked point gap and cleaned. put bike back to gether, checked plug to see if we are getting fire, have good fire. Now here is the problem, I cant even get the bike to fire. Nothing, Got tired of kicking and pulled with the 4 wheeler, nothing. At this point I am guessing that I have the cam aligned on the exhaust stroke.

My question is, with the motor tore down, ( cylinder and head remvoed) how do you tell which stroke is compression and which is exhuast.

I know this my be a stupid question, but I am stumped and need some help, have done everything that the manual says and am about to take an BFH to it.


Ok, with the help of a friend I finally figured out the problem, I am going to leave this post so that if someone encounters the same problem , maybe by reading it will help them, I had the motor timed on the exhaust stroke, and the way I found out was by watching the points as I turned the motor over, points closed on exhaust stroke, points open on compression stroke, that simple, some times the simplest of things will drive you crazy, Hope this helps someone down the road.

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C Bly

74 CR 250M
74 CRF 175
75 XR 75
77 ProFab Aberg HL500
97 Montesa Cota 315R
2003 CR500 AF
2004 CRF 450


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PostPosted: Tue Jan 29, 2008 9:38 pm 
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Joined: Fri Jun 02, 2006 11:12 pm
Posts: 159
Location: Salinas, CA
I am glad it works now, but hold on......
The lower end of the engine just rotates. It doesn't know the difference between compression and exhaust stroke. If the points are on the end of the crankshaft, they will open and the ignition will fire on both the compression and exhaust strokes. That's a wasted spark, but that's the way they are built right from the factory. The points just open when the crankshaft gets to a certain position, and it's all the same to them as long as the crankshaft is rotating.

The cam sprocket is twice the size as the camchain sprocket on the crankshaft. So, when the crankshaft turns once, the cam shaft has only turned 1/2 of a turn. It takes two turns of the crankshaft to spin the camshaft one full revolution. That's the only difference in the engine between compression and exhaust stroke - the position of the camshaft, and what it does with the valves of course. So, I think that camshaft might have been timed 90 degrees off. Your mark might have been aligned with the surface of the head, just the opposite side that it should have been on.

Sorry, I know it probably doesn't matter so much, right? What matters is that the bike runs, and that's a good thing!


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PostPosted: Mon Oct 20, 2008 12:57 pm 
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Joined: Thu Feb 09, 2006 6:10 pm
Posts: 51
mrmikkelsen wrote:
I am glad it works now, but hold on......
The lower end of the engine just rotates. It doesn't know the difference between compression and exhaust stroke. If the points are on the end of the crankshaft, they will open and the ignition will fire on both the compression and exhaust strokes. That's a wasted spark, but that's the way they are built right from the factory. The points just open when the crankshaft gets to a certain position, and it's all the same to them as long as the crankshaft is rotating.

The cam sprocket is twice the size as the camchain sprocket on the crankshaft. So, when the crankshaft turns once, the cam shaft has only turned 1/2 of a turn. It takes two turns of the crankshaft to spin the camshaft one full revolution. That's the only difference in the engine between compression and exhaust stroke - the position of the camshaft, and what it does with the valves of course. So, I think that camshaft might have been timed 90 degrees off. Your mark might have been aligned with the surface of the head, just the opposite side that it should have been on.

Sorry, I know it probably doesn't matter so much, right? What matters is that the bike runs, and that's a good thing!


BTW, Just to follow up on this post, the points on a TT500 dont run on the end of the crankshaft, they run on a secondary shaft that spins one revolution to every two revolutions of the crank, so what I stated earlier about finding the points open on compression stroke and closed on exhuast, is correct. I initially thought the same and I just had the side cover off of one the other day and the point shaft is a separate shaft in itself that is spun by the crank shaft in a 2 to 1 ratio, See pics below, gear # 2 in the first pic, runs on gear # 22 which is attached to the crank in the second pic. Hope this helps someone else when they are ready to pull there hair out like I was!!!!!!!!!!,
ImageImage

_________________
C Bly

74 CR 250M
74 CRF 175
75 XR 75
77 ProFab Aberg HL500
97 Montesa Cota 315R
2003 CR500 AF
2004 CRF 450


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PostPosted: Sat Oct 25, 2008 12:54 pm 
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Joined: Fri Jun 02, 2006 11:12 pm
Posts: 159
Location: Salinas, CA
:?

Thanks for straightening me out on that one.


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