GSF250 top end rebuild part III

**cbfb** · 3rd December 2010, 18:57

Hey,

You may remember me from such posts as Getting pistons back into cylinders and the slightly melodramatic Worst nightmare come true. Yep, I'm the one who's rebuilding the top end of his 250 Bandit. I know I should probably have involved a mechanic a week or two ago but hey I enjoy this stuff and I won't give up now, I think you can do anything if you put your mind to it. Plus financially it's either do it myself or not have a bike.

Well all has been going well, got the head on, checked that the crank rotates ok, no worries there. Put shims and tappets in, then move on to cams:
- Check crank is at TDC
- Insert exhaust cam, aligning timing marks as per GSX250F Service Manual p3-51
- Take up slack from crank sprocket then engage chain with exhaust cam sprocket.
- Insert intake cam, aligning timing marks as per diagram.
- Engage 16th pin from mark on exhaust cam with mark on intake cam.
- Fit and torque down journal holders, moving diagonally and across holders to make sure cams are bedded down evenly.
- Use screwdriver to wind back cam chain tensioner pushrod.
- Install tensioner, then release pushrod

At this point, the job should be done and the crank should rotate freely. Unfortunately (having attempted this 5 times already) this isn't the case. A few degrees of rotation and everything locks up. There seems to be a lot of slack between the intake and exhaust cams prior to fitting the journal holders which doesn't look right. At first I thought TDC is not right, but have checked with a wooden rod to make sure pistons on #1 and #4 cyls are right up. Have also tried putting intake cam in first instead. What seems to be happening is either:
1. As I'm tightening up the journal holders, the chain jumps back a pin (so there's only 15 pins in the link between sprockets).
2. The chain stays on between tightening, but as soon as I rotate the crank after installing the tensioner, there's a clunk and everything locks up.

I am thinking that it's the chain jamming somewhere (have looked down into the crankcase and can't see anything obvious). Have heard bad things about Suzuki tensioners in general (internet rumours, not sure what they're worth), so maybe that's at fault?

Anyway... if anyone could suggest what to try next I would be VERY grateful. The weather is great and I just want to ride, not be stuck in my stinking hot workshop

p.s. Please don't tell me to go to a mechanic, it's something I want to do on my own (with help from the generous folk on KB of course). And yes I know it would probably be wise to leave this to the pros, but I enjoy it so there

**cbfb** · 3rd December 2010, 20:18

p.s.s. Forgot, I have also checked the stretch in the cam chain, it's well within service limits.

**disorderly** · 5th December 2010, 04:51

sounds like your on track so far
Is the front cam chain guide been put in?
with engine at TDC pull chain tight upwards then insert exaust cam ,line up all marks as you have done then torque cam holders down, now pull cam chain ( not to hard upwards ) at rear to take up any slack and insert inlet cam again line up marks and check number of pins on chain between upper mark on ex cam and upper mark on inlet cam sprockets and torque down now make sure there is no chain slack in the front of cam chain is there a guide of some sort that fits over the chain in the centre between the two cams? held down with four bolts ? any ways insert cam chain tensioner ( the cam chain tensioner blade has been put in i assume ) as per instructed by manual check that the ratchet on then cam chain tensioner isnt worn it should click out but you shouldnt be able to push it back in now check engine is at TDC still, check marks on cam sprockets are still lined up ( ex can sprocket 1st mark at 9 o clock, 2nd at 12 o clock then 3rd mark on inlet cam sprocket at 12 o clock and count number of pins between the 2 , 12 o clock marks.
turn engine over by hand now what can happen here is as you slowly turn engine you may hear clicking from tensioner taking up any slack which may put cam marks slightly out but if it hasnt locked up as you described keep going cause you can only determine this once you have done a couple of rotations and go back to tdc again another thing was the marks on cam sprockets were just above the head surface or below and you could never get them flush so if at tdc if this is the case check those number of pins again if correct it will be fine
you do have a bit of slack when you have bolted the cams down thats why i asked if there a guide that fits in between the cams just make sure there is no slack on the rear of the chain where the cam tensioner pushers
now this should turn over with no probblems however as you said its locking up only after a few degrees of rotation hmmmmm........
if you turn engine both ways does it lock up in exact same place or does it do it at different points of rotation,check make sure nothing fallen down the plug holes

stuck valve check valve clearances
hope this is of some help

**cbfb** · 6th December 2010, 15:01

Hey. Thanks heaps for your reply. In response to your suggestions/questions: