Z1-B rotor bolt issue

[steve452]

Having lost the original rotor bolt I ordered a replacement from Cradley Kawasaki. The original was 114G0840 which has been replaced by 115BA0840. I had already checked the thread in the crankshaft with another M8 x 1.25 pitch bolt and found it to be very tight. I thought this was probably due to crud build up over 45 years so reckoned I would have to tap the thread out to clean it up. Upon receipt of the new bolt I checked it to make sure it was indeed M8 x 40mm, 1.25 pitch, which it was. It was also a tight fit only going into the end of the crank a few threads. I then started to tap ouut the crank but found I needed much more effort than I would have expected, to the point where I thought I'd jammed the tap in the crank, it needed so much force. I managed to extract it by heating up the crank end although it did make that horrible clicking noise as it came out. I installed the rotor assembly onto the crank and screwed the bolt in as far as I could by hand before it started to really bind but found the head was about 4mm short of the thick washer. I've attached a pic of the gap between the washer and the bolt head and also a pic of the whole assembly, which I'm sure I've installed correctly, with the concave face of the damper facing inwards. I'm loath to continue tapping the crank in case the tap jams again. Barring shortening the bolt can anyone advise what's going wrong?

[Al]

Which tap did you use? Start, middle or finishing tap? What came out on the tap? Was it metal or chewing gum type snot? If it was the later, it may be that someone has loctited the bolt in previously. If so, heat can often be used to soften some loctite varieties to make it easier to get out.Its a job to see but if that is a 40mm bolt then it is 1.25mm pitch. (32 threads showing per the length). If you have a co-responding 1.25mm die, i would run that up on the bolt thread because, although difficult to see, the first few threads look mangled. Looking at the parts diagram on CMSNL for the Z1B the bolt is only threaded half way and relieved the rest of the way. A fully threaded bolt will have a significantly higher friction effect than the original type. If the bolt is of good quality it should be OK but if its one of those nasty rolled threads the 32nd thread may not be the same distance apart from the 1st as it would be with a good quality tap. Meaning they go out of mesh fairly soon.
I believe the effective length of a thread is one and a half times its diameter. Only 12mm of an 8mm bolt it engaged (pulling) with the co-responding hole thread. If the thread in the crank is good i would maybe look to remove the damaged part at the end (first couple of threads) and see how that goes. Failing that, an original format one, if one can be sourced.
AL

[z1bman]

use a 8mm allen bolt coated in some fine grinding paste & wd 40 & work it gently until the new bolt screws in by hand also fit a schnorr washer under the bolt

[kev edwards]

You need carbide taps for this job as the crank is hardened, don't use grinding paste as I see you still have motor in the bike, so you won't get all the paste out.

[steve452]

As I said in my first post, the bolt is a Kawasaki original part 115BA0840 (replaces 114G0840) and was obtained from Cradley Heath Kawasaki. The bolt has only been finger-tightened into the crank and the blackening at the end is just 45 years of crud mixed with WD40 which I used as a tap lubricant substitute, thinking it was a straightforward tapping job. I've ordered a 5.5mm endoscopic camera, which should arrive today, in an effort to see what the state of play is inside the crank end, as I discovered a conventional torch and Eyeball Mk 1 can no longer focus well at these short distances.

z1bman - I note your point re the locking washer. I assume this goes under the bolt head on top of the thick M8 washer.

Kev - Re carbide tap. Have noted your point re hardened crank, which I should have remembered from reading previous posts on other matters on this forum. Doh! In my defence I would plead insanity brought on by personality type. I'm not sure if mine is a carbide tap, but if not I'll order one.

I was about to reinstall the top end before all these shenanigans, but if I can't get this sorted myself will have to strip down to the crank again to get a pro to sort it, so it's become a bit of a showstopper. Will let you guys know how it turns out, one way or the other.

Many thanks for all your advice which is much appreciated.

[zed1015]

I've run normal HSS taps down the rotor thread to clean them out no problem.
The material isn't that hard down the core and if you are just chasing the original thread then it should run through easily.
Even though it's supposed to be the correct bolt i would check to see if it's bottoming out or that there's an obstruction in the hole.
Is your tap long enough to reach as far as the bolt thread.

[Al]

What i was looking at was the CMSNL site and it said something other than that which you had written!

[steve452]

Al - the CMS site also states that the bolt has been superceded by 115BA0840 which is also what Cradley Heath listed and sent me. The CMS bolt you show is a 115 head ('Upset' head). John Brookes notes in the 6th edition of his parts book that "There are 3 types of 'Upset' head screws supplied by Kawasaki, namely 112, 115 & 116 but only the 116 version was used on the Z1 - Z1B." So if John Brookes is correct (and I have no reason to doubt him) the CMS bolt could not have been fitted to any Z1 as original equipment although they state that it can. It may well physically fit but that's another matter. The original bolt is a type 114 which is a plain hex head, not an Upset. The 115BA0840 bolt that Cradley Heath have sent me is the correct size, length and pitch. The problem I have is the crank thread itself. I have viewed the thread internally with an endoscope and although the focus is not that great at this distance (about 1mm) I can make out quite a bit of reddish crud which I believe may be locking compound. It may also be rust. The next stage is to order a TC tap and heat up the crank end to soften up the crud and hope that works. I've now removed the pistons, which I'd previously installed prior to hitting this glitch, so I can put a bar through all 4 little ends to lock the conrods and give me some purchase for the tap (unless someone thinks that's a bad idea re stressing the conrods?).
Zed1015 - The bolt or tap can't be bottoming out as the hole is about 106mm deep, although it may indeed narrow as it deepens. I did however manage to get the endoscope right up to the blind and the camera diameter is 5.5mm, so I don't think that's the problem.

Many thanks to you all for your interest and advice. I'll let you know how it pans out.

[zed1015]

What i meant was is the bolt bottoming out on the cut threads due to being too long but obviously that is not the case.
The cut threads in the crank only extend so far but can be cut further which i have done with a HSS tap in the past.
As mentioned if it's just old Loctite then even a carbon tap should shift it and for this application the use of a light oil for lubrication is all you should need.

[steve452]

Hi all..as mentioned in another thread the application of heat, TC tap, Molyslip, but most of all, patience has resulted in cutting a thread that will now accept the bolt full length.

Many thanks to all those who offered advice as it certainly saved the day (and another crank deinstall! )