Thumper engine rebuild - cam timing

The Other PaulG

The Other PaulG

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Hi there,

I am just in the process of re-assembling my DR600 top end.

When the 'T' on the flywheel appears in the crank case window, the piston's at TDC. Fine.

I assume that as the spark's triggered from the rotor, it's a total loss system, ie it also sparks a second time, 'unnecessarily', when the piston's at TDC on the exhaust stoke, too....

Therefore, if my piston's at TDC I can in fact instal my camshaft in one of two positions, 180 degrees apart, because all I'd be doing is designating its current position as 'top of comression stroke' or 'top of exhaust stroke'... it seems to me that for a single cylinder bike, this is logical.

However, the very last thing I want to do is to re-build then find that my timing is goosed.....

Plase can anyone (preferaby someone who has done this..!!) confirm?

Cheers,

PG
 
The Other PaulG said:
Hi there,

I am just in the process of re-assembling my DR600 top end.

When the 'T' on the flywheel appears in the crank case window, the piston's at TDC. Fine.

I assume that as the spark's triggered from the rotor, it's a total loss system, ie it also sparks a second time, 'unnecessarily', when the piston's at TDC on the exhaust stoke, too....

Therefore, if my piston's at TDC I can in fact instal my camshaft in one of two positions, 180 degrees apart, because all I'd be doing is designating its current position as 'top of comression stroke' or 'top of exhaust stroke'... it seems to me that for a single cylinder bike, this is logical.

However, the very last thing I want to do is to re-build then find that my timing is goosed.....

Plase can anyone (preferaby someone who has done this..!!) confirm?

Cheers,

PG
Click to expand...

If it is a total loss system then you are right - assemble it either way without a problem.

If you are in any doubt then align the crank at TDC and the cam with all the valves shut (normally all lobes down) and the cam sprocket timing marks aligned. That way its sure to be on compression when the spark fires. It also means its set up for when the head cover goes back on and you need to adjust the valves before running. Win win really.

LC
 
NB - just before the pedants start it should really be described as a 'wasted spark' system rather than a 'total loss' sysem which normally refers to two strokes without a separate oil pump system. I was going to leave it but then thought I couldn't stand the shame ;)

LC
 
just before the pedants start ...

Surely not! ;)

Thanks for the advice - it's great to have confirmation so if the bike won't start, at least I can tick timing problems off the list...

Cheers,

PG
 
Lou Can is 100% correct.

I took a DR600 from 15,000 to 63,000 miles, mind you it had several rebuilds along the way.
 
Pedant/on
Wouldn't total loss refer to either an ignition system run from a battery with no generator to recharge or a four stroke with no oil scavenging system as in some vintage and speedway engines. Pedant/off:rob :D
 
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