tight cam bolt

[davecut]

Hi guys, I don't seem to have any compression on my rear pot so have decided to take my head off. But the bolt in the exhaust cam wheel is unbelievably tight, I have put a 22mm spanner on the cam as per manual and i have a breaker bar on this bolt, but i am putting so much pressure on this bolt I am scared I will snap the cam. any ideas? is it possible to remove cam with wheel still attached. any ideas very welcome. cheers Dave.     

[The Prophet of Doom]

You don't need to take that cog off.
Just undo the chain tensioner, and the cam clamps and it will all come off easily

[fret not]

FIRST have you checked the valve clearance?  These motors have a tendency to wear the clearances tighter as they gain miles (kilometers), and they can wear to the point that some valves do not close completely.  That lets the compression escape.  If the clearance is within specs then it is probably the head gasket, BUT it is a lot more work  and expense to change a head gasket and then find out it was the only valve clearance.

[davecut]

Thanks for your replies guys. i have checked clearances and although they are very small around 4 thou on inlet they do have some clearance. As far as removing the cam my brother (who is a skilled bike mechanic) also seems to think if I remove the sprocket which will unbolt the other one will then have enough free chain movement to remove the other cam. so thats what I am going to try. I will let you know how I get on. Dave.

[davecut]

cams are out and yes you can take the cams out without removing the sprockets. the thread in the cam that I removed the sprocket from is absolutely mullered and will need recutting. this bike has been owned by a right bodger I am worried about all the other bodges that have been made on this bike. 

[davecut]

One final question on this subject the bolts that hold the cam wheels on, does anyone know what thread they are? they look about m10 and quite a fine thread possibly 1.0 or 1.25 it would be great to know many thanks. Dave.

[Walt_M.]

The factory service manual says it's M10X1.25 torque 50 ft. lb. Do you have a manual? You really need one.

[davecut]

Thanks walt, yes I do have a haynes manual, but I didn't think it would be in there, so I didn't look. which manual do you have? Dave.

[George R. Young]

For manuals, you might have a peek at this:

http://ridersofvision.net/rovforum/index.php?topic=12221

[Walt_M.]

Dave, I have the Yamaha factory service manual. The link George provided is excellent, lots of good stuff there.

[davecut]

An update on my progress, I decided the head had to come off but I found it very difficult to get the head to clear the studs so I removed the engine bolts, with a car jack under the sump, and eased the engine about a half an inch forward, this made it possible to remove the head. On inspection the buckets that hold the shims were very tight on the exhaust cam, so I super glued long 6mm bolts in the centre allowed to set (overnight) mounted a raised steel bar above them and wound them out. I left the bolts attached and used them to attach a drill and with fine grinding paste gradually seated them back in position. when I was happy they were moving freely I reground the valves and reassembled. So all seems good now and I now have compression back.
 I have never had this bike running, so the next step is to see if she will run. Dave.