Cam bearing cap bolt hole

So after adjusting the valve clearance on my gpz11 unitrack, of course the second to last and last cam cap bolt hole threads let go.

Held the cam down while tightening and didn’t torque down the bolts - just one of the joys of these bikes I guess.

I’ve repaired the outer hole with a helicoil. The problem is getting access to the last hole. Its right side inlet, inner rear.

I can get a drill bit in but its a couple of degrees off vertical due to the top frame rail. And i can’t quite get a angled drill adaptor in either.

I’m really trying to avoid taking the head off again as it was running great before and I’m sure the list of problems will just increase with more knackered threads etc etc

i was toying with the idea of pulling all the engine bolts so i can tilt the whole engine a couple of degrees to the right to get clearance for my drill bit past the frame fail and leaving everything intact.

Am i mad to try this or is there another way?

90 deg drill adapter and grind the tail end of the drill to shorten its overall length?
Not sure how much room you have between head and frame. 

98mm from rail to surface, so too tight for a right angle drill/chuck arrangement.

I may be able to just get in with a right angle hex drill attachment + hex stubby drill bit. I'm gonna try and source one locally tomorrow.

Pain in the ass really. I'm prepared to strip the head off and heli all the holes once and for all but I'm looking at a minimum 2-3 week wait just to get all the gaskets and other bits I'll need (I'm in australia)

Grrrrr!

I'd pull the engine mount bolts and tilt the engine to the side to gain working room before I'd pull the head.

wrote:

I'd pull the engine mount bolts and tilt the engine to the side to gain working room before I'd pull the head.

+100, move the engine over and do it right, that hole needs to be done straight. Make sure you clean up all the swarf...

Managed to sort it with an angled drill attatchment and cut a drill bit in half as warrens suggestion.

hardest part was modifying a heli tang punch by cutting a slot in it to become the insertion tool.

Also i’ve ordered some stubby drill bits to use for next time,

Did you by chance take any pictures of your repair process Woodyvale?  It's always good to see how people make repairs in situations like this.

Rick H.

Sure, here's a few pics.Only other thing I would recommend is using a can of compressed air to blow out the debris from the tapped hole (watch your eyes). 
I left the cam in place on the cam chain as I'd already done the shims and didn't want to retime it. Didn't make any difference to working space.
The tools I put together will come in handy again I'm sure.

When blowing out the holes, a compressor is better of course, blow the air close across the top of the hole, it creates a venturi effect and sucks everything out, this method is great for blind holes when trying to get particles out after sand blasting.....

This is a tip I read from a guy that maintained a fleet of KZP's for a police department-
Because his job was to get the bikes back on the road as quickly as possible.. when having to deal with an occasional stripped cam cap bolt hole.. he said, rather than messing around with inserts, which would be the proper method, he would used a hardened 1/4-20 bolt and thread it right into the stripped threads of the hole without further preparation. He claimed the bolt would hold the specified torque and to the best of his knowledge he never saw one come back for that failed bolt. 
Yes, it is a quick and dirty hack but he said it worked. I do not recall if he used a thread locker.
If I can find a link I'll post it.

It may be worth a try. Worst case situation is you're going to drill it anyway.

I picked up one of these last year and it worked great to get the hole lined up correctly.  www.eastcoastadditive.com/samples-of-pro...-cam-cap-drill-guide
 

Blipco, i was getting to the point of doing something like that! Luckily I managed to get an insert fitted. Took me ages though.

referman - that guide is awesome! Will see if i can source something similar here in oz.

just received my stubby drill set to fit my right angle drill attatchment - think i’m gonna need it as one of the cam cover bolts is feeling dodgy.