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Running valve lifters with Mk5 TP cams

Brian Thompson

Well Known and Active Forum Website User
VOC Member
Hello Everyone,
Is anyone running valve lifers with Terry Prince Mk5 cams?
I have fitted the valve lifters into the timing chest to see if there is a clearance problem with these high lift cams. Well yes there is.
I'll have to modify(grind and build up) the valve lifters if I'm going to continue this way.
I have twin plug heads,but I have a BT-H 4 plug magneto ( Electronic distributor) for this engine. I was hoping to keep it that way,rather than using 2 plug holes for an external decompressor set up.
I'm curious to see if anyone has successfully used the original set up with some modifying?
Thank you
brt650
 
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roy the mechanic

Well Known and Active Forum Website User
VOC Member
Hi, i've "only" got the mk4's. the lifter now works after literally days of grinding+ fettling. It may be worth considering looking at the big capacity h-d compression release valves i believe to be avalable from s+s in the states, watch out for binding bothers in the rocker arms and valve collars knocking the life out of the valve guides! good luck, please report back on the ammount of agravation you are about to have, Roy.
 

Monkeypants

Well Known and Active Forum Website User
VOC Member
When I enquired about this prior to purchasing the "last ever" set of Mk fives, Terry sent me a photo of some Mk 5 s with decompressor installed. He did say fettling was required.
I wonder how many of those last ever sets of Mark fives have been sold?

Im in the same boat but with Pazon 4 plug ignition, a special setup that pulls twice as much power as the regular Pazon 4 plug Vincent ignition. Same as you, I want to use all the plug holes for spark plugs as the designer John Trease intended. Anybody who can coax 58 rwhp from a 500 cc Comet(John Trease built for Ian Boyd) gets my undivided attention.

Glen
 
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Monkeypants

Well Known and Active Forum Website User
VOC Member
The Sputhe 5/16" item is interesting. With the two plugs installed in these Prince heads there isn't much room left, but a 5/16 hole might work. One clear advantage is that this type of decompressor can be used with estart while the stock type really should not, it is too fragile.

Glen
 

roy the mechanic

Well Known and Active Forum Website User
VOC Member
anyone who can acheive 58 horses from a comet should be awarded one of my mums putty medals or told to go away! The best original manx norton made 51! Ray Petty should know-as he built it for Derek Minter, the king of brands.
 

Monkeypants

Well Known and Active Forum Website User
VOC Member
John Trease did this,confirmed by Rodney Brown , who visited my shop last month. Rodney is an Australian Vincent owner and me
talurgical engineer for the giant Foundry Company Esco.
He was responsible for the foundry work on the first TP heads, and was involved in the RTV Vincent. He later sold the patterns to Terry, although Terry has made careful changes along the way, they are still pretty close to John Trease's original design. He had some criticism of the cosmetics on the new TP heads, didn't care for some casting spurs left between the cooling fins. He claims the design is very effective. He told me that a 600 Comet with these Trease/ Prince squish heads will walk away from a standard Rapide/Black Shadow
 
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davidd

Well Known and Active Forum Website User
VOC Member
OK Glen, I guess we have to believe you!

This is the Vinton that I posted photos of earlier in the post entitled Ian Boyd Black on Black. Greg Brillus has been chatting recently with both John Trease and Ian Boyd, so maybe he will jump in and give a little more info in the post on the General Chat forum. I have posted some additional info there.

Just so we do not hijack Brt's post completely, what Glen says about careful fitting would ring true to me. Terry usually does mods that work within the existing set-up. However, the lifter is not a very robust mechanism. Many racers remove the lifter for that reason alone, so I cannot think of another owner that has done your set up.

David
 
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Brian Thompson

Well Known and Active Forum Website User
VOC Member
Thank you for your responses.
I decided to call Terry this afternoon. I guess I could have done that first. But I don't like to annoy him any more than I need too.
Terry agreed with what Roy stated and that is, the original set-up can be made to fit with some careful preparation.He gave me some advice as usual and I'm happy to go ahead with that.
Thanks again
brt650

Just for future reference if your going to fit some of these cams,(whether they are the last set available or not) be prepared to trim the inside of the timing chest to give the new type followers travel clearance.The areas around the rear cylinder inlet follower and the front cylinder inlet follower. And don't forget to relieve the rear cylinder exhaust follower for clearance of that cylinders camshaft wheel.If you look at the originals you will see that they have been relieved in that area. Hope that makes sense? Also purchase the new Socket Head Tappet Adjuster's ET27V3 or it's equivalent for added clearance in the tappet covers.
 

Monkeypants

Well Known and Active Forum Website User
VOC Member
There is a bit of an inside joke to the "Last ever" mention. I believe it was John Mead who posted about buying the last available set of these cams awhile after Terry sold me the last available set.We decided it wasn't possible for us both to have the last available set so one set must be the penultimate last set and the other just the regular or common last set.
Now there are more showing up. This is a good thing, it means Terry is feeling up to the task of getting more parts made and carrying on with his business.

Glen
 
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