hi there im putting the dragstar 125 heads and cylinders on an xv virago 125 engine too see what happens they fit perfectly but the timing of the xvs heads is different to the xv all i need to know is if this is in order or if its wrong i.e the valve opens or closes b4 it gets to tdc or bdc.

tdc = exhaust valve closed -

air valve opens - piston goes down

bdc = air valve closed -

piston goes up = compression

tdc = spark -

piston goes down

bdc = exhaust valve opens -

piston goes up

cheers .Paul.

im guessing no one is sure to post a reply so im gonna go and have a fiddle

The timing is controlled by the cam shaft, not the heads. If the direction of rotation of engine is the same on both bikes, the cam shafts will be set to work in the right sequence. The timing of the valves might be different though. If there are differences I'd check very carefully what they all are. Yamaha may have changed the number of teeth on the drive sprockets, for example - hours of fun if you put the wrong cam drive with the wrong crank drive ratio. They have done this on numerous occasions in the past with different models.

You are going to need to build up the engine and use a DTI to measure the actual movement of the valves and compare them to the spec sheet for your engine.

Good Luck!

well... iv actually managed to fit the heads on and sort the timing out by using the list iv made and seeing when the spark plug sparks, and all is well! im quite surprised how well its worked out considering all iv got is some spanners and a ratchet set still a couple of kinks to sort out but it starts, runs and drives really well i dare say its slightly better with the new heads but yeah im gonna have a play later on in the week to see if i can smooth it out a little better cause at the end of the day it was just a good estimated guess to where the sprocket should go on the chain in relation to the timing on the engine to the timing on the heads. so yeah il keep everyone updated when i get some work done.