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Help with Studs

steve cassel

Forum Website User
Non-VOC Member
I'm hoping someone can point me in the right direction... I have some cases from John Wyatt, and have found that my cylinder studs will only screw in a few turns before they bind up. I suspect the cases were tapped wrong, but I have been unable to identify just what the stud threads are.

Has anyone else experienced this problem? I'd like to find some taps and dies to chase all the threads, but I'm not sure what I need. Any help or input would be appreciated.

I have also noticed the spindles on the timing side don't screw in easily. I suppose I'll need taps for those also, though I haven't really given them much attention yet. At least all the cover screws fit nicely:).

-------Steve.
 

Chrish

Well Known and Active Forum Website User
VOC Member
Steve,

It sounds like JW came good in the end. Be very careful of the cylinder studs, Dag, from Norway damaged the cases putting these studs in his new JW cases. Go around the cases and put through a tap in all the threads. This is necessary, You're in TX ask at your local section for the loan of specific taps, I'm sure you'll get help. What screw in timing side spindles are you having trouble with? Good luck with the build...

Chris
 

steve cassel

Forum Website User
Non-VOC Member
Taps

Hello again Chris.

No, John W hasn't come through for me yet, though I did receive bare heads and cylinders from him since the last time I talked to you. I'm still needing everything on the timing side, everything on the drive side, the complete valve train, pistons, everything under the kickstart cover (plus a kickstart cover), and a few dozen other bits to complete my motor. I haven't been able to reach him on the phone since I got back this month (and no email response either). I'm beginning to wonder about his health. Anybody heard from him?

I don't know anybody in the local section here in Texas just yet... I'm still waiting for my VOC membership to take effect. I don't have full access to the site yet (though I do have my Member Number now). Patience, patience, patience.

I don't mind buying taps and dies, though I'm afraid the one for the cylinder studs is a real oddball. On the timing spindles, I would have to go back and check again but I suspect all of them will need cleaning up. Some spindles would start reluctantly, some not at all. Could be they were tapped with the right pitch but the wrong pressure angle? I hope Dag was able to correct his cases without too much difficulty. Does anyone make helicoils for such uncommon threads?

At any rate, it's good to hear from you. Hope your project is coming along as well.

-------Steve.
 

Chrish

Well Known and Active Forum Website User
VOC Member
G'day Steve,

Sorry to hear you are still having trouble with the Norvincentre, when we were in the UK, recently, Phil Pilgrim went to see John, to get the money owed to him for a few years, John paid up when Phil propped on his door step. You should not have to go to extremes to get what is rightfully yours, how long have you now waited for John Wyatt to deliver what he has no doubt continuously promised.

Something else to make sure of is the oil pump chamber, the depth and, on the cases supplied to me, it was tapered. This is critical because should you force the OP32AS in, things could be difficult to rectify. I've been told that four sets of cases delivered to Australia have all had this same problem.

Regards,

Chris
 

Howard

Well Known and Active Forum Website User
VOC Member
Steve

Just a note of caution. This is definitely a "measure twice cut once job" think through all the options before you start cutting metal.

I don't know the exact problem with the differences in the threads, but if you run a different tap down the thread you may end up with a very weak thread, or the new tap may take out the old thread completely (worst case). If the threads are very different, you may be better having new studs made rather than weakening the threads in the cases.

If the studs start in the thread, then tighten, there is a possibility that the threads have only been cut with a taper tap, it may be as simple as running a plug tap down to the required depth.

If the worst comes to the worst, there's always Helicoils - the manufacurer tells me they are not just for repair.

I don't want to be a harbinger of doom, but make sure you know what the problem is before you try to fix it.

H
 

steve cassel

Forum Website User
Non-VOC Member
Still Taps

Howard, Thanks for the response. I was hoping someone 'in the know' would offer up the solution and tell me where I can buy the correct tap and die.

I did measure the thread pitch for both the (original Vincent) cylinder studs and the (reproduction) cases. Both the studs and the cases are 20 tpi according to my thread gauge. My very-near caliper tells me it is a 9/16 diameter. I'm guessing the hole is either a little undersize, or there is a difference in pressure angle... (55 degree? 60 degree?) Hard to imagine how the hole could have been tapped a little small... I'm guessing it's the PA. Either way, If I can find a tap that matches the original Vincent studs, it should chase the threads out quite nicely and I'll be back on track. I just need to know the proper tool and where to get one. And yes, you're right... I'll have to remember to get a 'plug' tap... Thanks.

Chris, Thanks for the heads-up on the oil pump problems. I haven't gotten that far yet, but I'll definitely check it. Seems like some of the cases fall into the list of "lumps which are suitable to make Vincent parts out of".

Regarding John W, I will have been waiting a year come November. I know there are people who have been on his list longer. I thought for a while that I might come and camp out on his doorstep myself... My daughter was looking at Maynooth College in Ireland, but chose to go to school in New York instead; so I guess I'll have to wait for another good excuse for a trip to Great Britain. Maybe I could convince my better half that we need a vacation...;-).
 

Prosper Keating

Well Known and Active Forum Website User
Non-VOC Member
For the record, these holes should be threaded 9/16" x 20 tpi (twists per inch). It could be that the threads are simply a bit tight but it would be a good idea, given the cost of the cases, to buy or borrow the right tap and run it down the holes just to be sure.

Might also be worthwhile getting someone experienced from your local section to take a look as it would not surprise me in the least if the threads had been cut with the wrong tap, given the source of the cases and the experiences of a couple of friends who had him work on their Vins.

In that case, if you're looking at the wrong threads, you might consider having new cylinder head bolts (ET55/2) made up with the appropriate threads. Or boring out the holes and fitting bronze inserts with the correct internal threads to accept the standard ET55/2.

As for the threaded spindles, you are presumably referring to the front exhaust cam follower spindle, which threaded 7/16" x 20 tpi, so the hole should be threaded accordingly. The other spindles are an interference fit and you must warm the cases, ideally in an oven for even heat distribution, in order to fit them. The studs on which the steady plate mounts thread into 1/4" BSW holes and take 1/4" BSF retaining nuts. So, again, verify that the holes in the crankcase/timing chest are correctly threaded.

PK
 

Mark Fisher

Well Known and Active Forum Website User
VOC Member
steve, I think it would be a good idea to get some help with these cases as the quality of some of the work seems to be suspect. I would suggest you talk to glen bewley in tennessee, he will be able to either correct the threads or make studs to fit (his shop is very well equipped), I would also have him check (and correct if necessary) the oil pump bore, cam spindle holes etc. It is a shame that after waiting so long these case are really not properly finished, but you have them now so I guess you have to work with what you have. My egli has molnar cases which (in my case) didn't have any issues, so obviously it can be done.
thanks
mark
 

Howard

Well Known and Active Forum Website User
VOC Member
Steve

9/16" 20 TPI taps available on ebay - RDG Tools.

I think this was a common thread in the 50s known as cycle thread and if memory serves me correctly it was 60 degrees.

One word of warning - the taps on ebay seem very cheap at £7 ish, but it may be a starting point - a cheap tap broken in the hole can be a real problem.

H
 

steve cassel

Forum Website User
Non-VOC Member
Tap Found

Howard and Prosper, Thanks.

A friend of mine works on bicycles, and had a 9/16 20tpi tap. That happens to be the thread used on English crank pedals. I still don't know what the pressure angle is, but I chased the thread in one hole with it and my cylinder stud now screws in happily. I'll check the ebay vendor for a bottoming or 'plug' tap so I can be sure to get all the way to the bottom with it.

Aside from the 7/16 x20 and the 1/4 bsw that Prosper mentioned, are there any other extraordinary threads that spring to mind? Looks like I'll be ordering some taps and dies.

Thanks again.
 
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