pistons and cams

debby · Sep 3, 2005

Well I'm confused. Overwhelmed with choices actually. I'm trying to decide what pistons and cams to go with for my rebuild. I wanted to increase the performance a bit, hopefully without killing midrange or hurting reliability.

Pistons: some people told me I should accept nothing less than genuine Hepolites (apparently hard to come by these days). Others say the GPM (?) pistons are ok. And Fred Eaton of OldBritts just told me that his inexpensive "economy" pistons are just fine if used with quality rings. Said he just put a set into his personal Mk 3. I'm reluctant to put cheap chinese parts into my bike but they are very attractively priced. However, my last experience with cheap chinese parts (petcocks) was not good.

Cams: I've been favoring the Megacycle 560 N-R. The guy doing my head work likes the WebCams 12A. But Fred also told me the stock cam is just fine for street use and in his opinion I'd be wasting my money on an aftermarket cam (my old one is fine for reuse, no wear at all). He says guys use the stock cam on pro dirt track racers! So now I don't know what to think about that either!

I welcome opinions and comments, to add to my confusion

Debby

Nithburg · Sep 3, 2005

Hi Debby,

I'm going through the pains of an engine rebuild with my bike too. I decided to go with the econo pistons and "Norton" (Italian) rings. I figure that if the Taiwanese pistons are as bad as some people think they are then reputable wholesalers and dealers would have stopped carrying them by now. Especially when you consider that you can make more by selling a set of $200 pistons as opposed to a set of $60 pistons.
I was seriously considering the Megacycle cams, and probably would have gone that route had they been in stock. In the end I chose to go with the 2S (Combat) cam.

Gary

WMW · Sep 3, 2005

Debby,

Not going to use the Teikokus? I'm thinking of putting a pair in my rebuild. Did you ever compare their weight to standard Commando pistons? Are the valve cuts the same size as Commandos? Consensus experience re Asian piston replacements seems to be positive. I'd guess you'll need oversized pistons however since you'll probably rebore your barrels as part of the rebuild. I did.

I, too considered cam options and ultimately bought a new stock Norton cam.

I share your pain!

Bill Walker

debby · Sep 3, 2005

WMW said:
Debby,
Not going to use the Teikokus? I'm thinking of putting a pair in my rebuild.
Bill Walker

The Teikokus are std size and to get proper clearance we need to rebore 1st over. So I guess I can't use them. It's too bad, they appear to be very high quality

Those pistons are a bit of a mystery. The box said "Norton Atlas" but they have slightly domed tops and a higher deck height than std Commando pistons. Deeper valve cutouts too. So I'm not sure about the CR but appears higher than std Commando. The box is also marked "II.I" - 11 to 1 CR??

Before using them would be a good idea to measure the actual CR and maybe use a cylinder base plate. If they're really 11-1 that's too much for street use.

Debby

Ron Hulton · Sep 3, 2005

Debby
Confused ???? When something is half price i begin to wonder if it is only half as good. I rebuilt last year and my dealer advised me to use only the Hepolite pistons which are not hard to get at all. He does sell the cheapies but probably to stay competitive with everyone else. Some people will pay as little as possible regardless of quality. If your rebuild is done properly it should be years before you ever have to go back inside. Why gamble with a possible inferior part. If you are oversizing the bore remember , get your pistons first so the machine shop can measure them and then bore to the actually piston size

If your cam is ok , reuse it . After all this time and it is still fine . That in itself should answer your question.

Good luck

Jason Curtiss · Sep 4, 2005

Deb,

I agree with Ron; if you find your stock cam is still in good shape, reuse it. Also, Hepolite pistons are high quality - forged aluminum alloy I believe. I easily found a pair at Raber's Parts Mart.

Jason

Steve Jowett · Sep 5, 2005

Deb,
The GPM pistons are of good quality, and I would use another set anytime. I have run these in the Norton Race Rig for the last 4 seasons. It runs the track consistantly between 4500-7000 rpm, and has surpassed 9000 on mis shifts.
As for the China pistons, my response is let someone else be the test pilot. Time will tell, and as others stated go in once and ride in peace of mind.
For cams if the stock one is good I would stick with it. When you get into alternate cams, there is a myriad of other problems. Valve to piston clearance, rockers misaligned, springs, even the lifters can be wrung the wrong way and drop their feet (Derek Wilson mentioned it elsewhere). Easy to check a cam shaft for use, just a set of vee blocks and a dial gauge. Just need to confirm lift is within factory specs, takes very little time and effort.
Lastly Hepolite pistons are still available although not necessarily in the bore size you need. The .010" to my knowledge have been gone for over 10 years. They would be my primary choice, as they are proven and of good quality.
More confused?
Hope this helps,
Cheers,
Steve Jowett

debby · Sep 5, 2005

I think we have a concensus.

"economy" pistons: No!

stock cam: Yes!

So Hepos or GPMs it shall be. And I guess I'll just reuse the stock cam instead of going for the hi-po aftermarket one. I can live without all those fitment issues.

Thanks guys!

Now - anyone know where I can get my stripped-out oil pump mounts welded and remachined? :?

Debby

Derek Wilson · Sep 6, 2005

Debby,

Your oil pump mount, is it so bad that it can't be helicoiled? That would be my first choice in repair.

It doesn't have to be 5/16"-26. 5/16"-24 will work just fine. Just change out the studs/nuts.

Cheers,

Derek

debby · Sep 6, 2005

It's already been helicoiled but they botched the job and the helicoils aren't holding. Also, the case is cracked at the lower stud mount. So the old helicoils have to be removed, the crack has to be welded, and the threads have to be repaired somehow (welding and retapping?)...

Debby

Derek Wilson · Sep 6, 2005

Well, if you feel like shipping it to Canada, there is a guy that Bruce Chessell uses to do his aluminum repair work named Kevin Watson. He would be my first choice.

If you're interested, contact Bruce about it: www.tritonmaching.com

Cheers,

Derek

Ron Hulton · Sep 6, 2005

Deb
This job needs to be done by someone who knows what they are doing. Locating the holes back in the same spot will take a bit of careful work or else you will be certain to have a problem with the oil pump drive gear and its alignment.

Again !!! second best means $$$$$$$$$$$$$$$$

Good Luck

Scooter62 · Sep 7, 2005

Debby
Hate to say it but as Ron pointed out the work you need done is more than a little difficult. If I were you I would seriously try to find a good set of used cases. These should sell for say $500 or less (new cases are around $1000 I think). The welding and machining cost could easily approach the cost of a set of used cases, if you can find someone that knows what they're doing. If you do opt for new cases they are the newer reinforced type.
My 2 cents,
Scooter

Jason Curtiss · Sep 7, 2005

Deb,

Welding Norton cases is tricky, owing partly to the oil trapped in the aluminum pores. However, a person skilled at tungsten inert gas (TIG) welding should be able to make a solid repair, but it will be costly. And after welding, the oil pump mounting holes will need to be drilled and tapped and the mounting face milled perfectly flat and parallel to the original surface - more $$$.

Also, machining the oil pump flange face to clean up the welding around the bolt holes means the pump will sit deeper into the block (unless the complete face is welded and then machined to original specifications). There are two potential problems with moving the pump deeper into the block: a) less preload on the sealing washer because the pump has moved away from the timing cover and b) the position and engagement of the oil pump gear relative to the crankshaft gear will have changed. Obviously, the more material that must be removed, the more serious these issues become.

I believe your cases can be repaired but I’m afraid it will be expensive and there are several opportunities for mistakes. Perhaps used or new cases are in order.

Jason

L.A.B. · Sep 7, 2005

Consider using TAPPEX ENSAT self tapping thread inserts to repair the pump stud holes:
broken link removed
These things WORK!
All the old helicoil would need to be removed from the hole to fit them but they are stronger and more secure than a helicoil, will probably work even with a cracked casing.
It may be necessary to make a couple of new studs if the correct insert internal thread form isn't available to match the studs?

The stud holes on late Commandos were helicoiled originally by the factory.
The torque settings given for the later oil pump mounting stud nuts is apparently incorrect and should only be 10lb/ft.

nortonfan · Sep 11, 2005

Debby,
Have you heard of "Devcon" ?
It is a compound mixture that sets as hard as steel.

If your oil pump stud holes were good enough to hold the oil pump in the correct position before your teardown, I would bet that you could do the job with devcon & it may last for many years if you clean the material up with acetone beforehand.

Just another idea to throw at you. I can tell you that "devcon" does a very good job. Just clean the stud holes & studs, then mix it up & pplace some around the studs & screw em in. Assuming the stud holes are still very reasonable, this should work for many years.

If you do not "flog" your norton, the cheaper psitons will make no difference except for saving more $$$$$.

kommando · Sep 11, 2005

25 years ago I stripped a thread on a BSA unit single gear cam spring pivot, I put the stud back in with epoxy glue and on strip down this year it was still firmly in place. The pivot takes more side pressure than an oil pump stud so I am sure a bigger size insert or a epoxy type repair, an oil pressure gauge will be enough insurance.

debby · Sep 12, 2005

nortonfan said:
Debby,
Have you heard of "Devcon" ?
It is a compound mixture that sets as hard as steel.

I've never heard of this stuff before but a quick web search found their website. It sounds interesting. Apparently they sell a variety of products, for industrial applications.

Reg, which of their compounds are you thinking of? The "Plasic Steel" perhaps? Here in the USA McMaster-Carr has it, in sizes ranging from a 2 oz tube to a 25 lb "bucket" (could fix a lot of stripped studs with that!)

For the short term I think I'm going to buy a rebuilt Combat motor from a friend in the club and install that. He did the work and knows what he's doing so I trust it. Then I can rebuild my motor as a spare. I was going to part it on ebay but having some spares on hand seems like a better idea.

Debby

kommando · Sep 12, 2005

If the current engine number matches the frame keep the crankcases as what you sell them for will be reduced by the loss of matching numbers affecting the bikes value.

debby · Sep 12, 2005

original motor got blown up at some point in the past. This will be the bike's third (at least) motor.

Debby

pistons and cams

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Nithburg

WMW

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Ron Hulton

Jason Curtiss

Steve Jowett

debby

Derek Wilson

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Derek Wilson

Ron Hulton

Scooter62

Jason Curtiss

L.A.B.

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