Topic: Melted Cam Chain Guide

[revhappy]

Just begun resto on my K8. Upon opening the head, the location where the Cam Chain Guide sits has melted. In the pic below u will notice remaining bits of really hard plastic hanging out from the chain path and a groove. Its my first time on a rebuild.

1) Why is the plastic bit hanging out from the case as if it was permanently fixed to the cylinder?
2) Is the groove there as standard or did the loose chain shatter the guide and further went on to rip off the metal on the wall?? If so do i have to replace the bores?

Any other observations u can maes in the pics will also help!

Please help?

[razor02097]

was there a guide there at all?  It almost looks like someone forgot to put it back in 

[Bodi]

That guide is badly worn, and broken. New guides have a "rib" down the middle that goes between the chain side plates, the grooves develop as it wears. The guide springs a bit when compressed between the head and the socket at the bottom, bowing inward to control the chain movement. If the chain is too loose it whips around wildly, maybe that's what broke the guide?

[bryanj]

Been run for way too long with a loose camchain so the chain and all the tensioners will be toast

[revhappy]

That guide is badly worn, and broken. New guides have a "rib" down the middle that goes between the chain side plates, the grooves develop as it wears. The guide springs a bit when compressed between the head and the socket at the bottom, bowing inward to control the chain movement. If the chain is too loose it whips around wildly, maybe that's what broke the guide?

What do i do? Do i need to buy new bores or is this fixable? Pls let me know where to go from here?

[Bodi]

The bores will be fine. Some models have the oil gallery across the front of the engine located where a really loose chain will cut into it, resuling in oil pressure loss and big trouble. But that's pretty rare. I'm not sure if the 750 is prone to this though.
You have to clean out the melted plastic and replace the guides... and a new chain would be a good idea. Make sure the tensioner unit works properly, on a 750 it comes right out the back of the cylinder block as I recall. There are also some rubber blocks the blade ends go into, these should be replaced if you can get them.
The original cam chain is endless, and requires disassembly of the lower cases to replace with another endless type. It's common to cut the chain and replace it with a riveted link type. You can get a stronger chain than stock as well, either endless or link type. I haven't heard many problems using the riveted link. Don't try and use a clip type master link, the chain speed and sprocket size will cause the clip to throw off at high RPM.

[damerlasudhir]

Thanks for the replies everyone. Sorry for butting into the discussion, but Im the guy helping revhappy fix this bike. Just wanted to reconfirm , the the guide was indeed present, but must have got whipped around as the chain loosened. Does it imply a faulty tensioner? Also the head also has a little grove (similar to the one on the cam chain well), but as far as I can see there should be no issues there. Now with so much metal missing , do you guys suggest a complete clean of all the oil passages and pump? Also can you guys advice me the best way to go about this?

Im just hoping that the new guide will fit in properly without giving issues. The top mounting point seems to be intact. Does the bottom have a similar mounting point too? (Sorry for stupid Q, but im 750 km away from the bike right now / Visual check not possible!)

[razor02097]

I have no clue with the dry sump system.  On the wet sump I take the oil pan off and look at the screen to see if metal is there.  Definitely check the oil pump though the impeller gears may be worn out by now.