New rebuild gone bang !

[the_dixtar]

Fired up my bike earlier after fitting new piston, valves etc it ran sweet for 20-30 seconds then after a few revs she cut out with a bit of a "snap" noise. pulled the rocker cover off to check straight away and found the inlet cam has slipped 2 teeth on the gear. Is there a way I can re-calibrate the cam? and secondly is there a way I can check if the new valves have been damaged without pulling the head off again?

And anyone got any idea what could have caused this? everything was torqued down correctly and the cams were spinning freely before starting her up.

[the_dixtar]

Just pulled the head off and the valves look fine, no little marks or anything on the valves or piston and their holding fluid so all looks good ?

I found a kink in the timing chain on 1 link, not sure if it was there before but I didn't notice anything when putting her back together. Anyone think that could have caused it?

[gnarlycharly]

why didnt you replace the cam chain when you did the top end? they do wear out and stretch, idk why people insist on using a cam chain that could potentiolly break.

[the_dixtar]

The cam chain had less than 5hrs use. I changed it along with new cams and only used the bike 2-3 rides so didn't see the point in throwing a chain with such little use.

I didn't notice any damage to the chain when I re-fitted it so I'm assuming it's from this incident. I'd like to know if it could have caused it to happen if it was there before so I can at least rule it out as an issue.

[KX290F Pilot]

Had this problem once when converting to Stainless Steel valves. The heavier springs needed wore the cam chain out and a cam jumped a tooth from a kink in the chain. Check your cam tensioner also. I always reset it after redoing the top end. If it goes to maximum tension and you install it that way it can make the cam chain way to tight.

[D-K]

Inspect/replace tensioner.

If you listen closely when installing the spring, rod and cap to the resetted tensioner, you hear how many clicks the tensioner goes out. When brand new it goes out 3-4 clicks. If it starts going past ten-twelve clicks(with a new chain), something is worn.

[the_dixtar]

I've gone for stainless now and had this issue. With all the new valves fitted is it normal for the exhaust valves to feel harder to push down on the springs?

I replaced the tensioner when I fitted new cams not long ago. I get around 5 clicks when I rotate the engine by hand after fitting the tensioner.

going to get the cam gear re-calibrated and iv'e ordered a new chain so once that arrives ill try putting it back together and try again. just hope it works fine this time round.

[KJ790]

Check your cam journals for scoring. If the cam caps were not torqued right then you can seize a cam momentarily and cause the cam chain to jump.

As far as checking the cams, you should probably go through the process of degreeing your cams to make sure that the cam sprocket did not slip on the cam at all.

[the_dixtar]

Check your cam journals for scoring. If the cam caps were not torqued right then you can seize a cam momentarily and cause the cam chain to jump.

As far as checking the cams, you should probably go through the process of degreeing your cams to make sure that the cam sprocket did not slip on the cam at all.

I marked the cams when I bought them brand new just in case the cam gear did move. So luckily i've got a reference point to put the gear back to now ? ill be adding a few spot welds to try and prevent this from happening again.

[D-K]

Richard Starr, it´s normal for them to be harder. The springs have different part no´s and are different weights.

From a performance point of view, the springs should be installed with the tighter wound end down. When fitted this way, the lighter end of the spring does the moving back and forth and it can make a difference on high revs and in the long run to have less reciprocating weight.

[the_dixtar]

Richard Starr, it´s normal for them to be harder. The springs have different part no´s and are different weights.

From a performance point of view, the springs should be installed with the tighter wound end down. When fitted this way, the lighter end of the spring does the moving back and forth and it can make a difference on high revs and in the long run to have less reciprocating weight.

Fair play DK you know your sh*t ?

Another lesson learnt on how to fit my valves Had my new cam chain today so ill be having another go at getting her running on the weekend?

[D-K]

Fair play DK you know your sh*t ?

Another lesson learnt on how to fit my valves Had my new cam chain today so ill be having another go at getting her running on the weekend?

Good luck!