chrisf1 said:
Hi again everyone I will say what I would like to do on my rebuild and am looking for criticisms, advice, and why, I am building another pre unit bottom end to swap out with the existing one in my bike which is dynamo cases with the dynamo hole blanked off and running an alternator it is also running the old school distributor which I dislike so I first wish to get the bike running again with this engine which before I pulled the primary side and gearbox off was running quite well, first problem, I would like to run without a battery (difficulty mounting with intended alloy oil tank ?), I intend to go with electronic ignition a new alternator (which one ??) as the one on it is suspect the red ignition light stays on when the engine is running ??? Next problem I am running an AMC Norton gearbox/clutch and wish to go for a dry primary belt drive should I go for a Triumph box for ease of final assembly or will the existing box not be a problem it does drip oil by the way what oil should it run on, well thats the start but it will be time lengthened by funds so suggestions of the best places for buying all of this would be a great help, I am in to deep to stop but unfortunately the pocket will restrict me so if anyone has any of the stuff I am looking for in good nick please contact me I already have 6T alternator crankcases and a big bearing crank and con rods (unit), rev counter timing chest, I am also considering a Morgo rotary oil pump ???? I will need camshafts E3134, timing gears. and possibly another (650 or 750) 9 stud top end, all advice, criticisms, and offers greatly appreciated, many thanks Chris
Chris, on a 360 degree twin a mag is perfect. A well reconditioned mag works very well on a Triumph. Remember adding a fancy mag to a unit Triumph engine is considered an upgrade... So why not stick to a mag on your pre unit engine, good performance, good looks, battery free and very reliable.
Ref top end, IMHO there is no reason whatsoever to stick to 650 if your having to buy parts. The extra 100cc adds a lot of oomph and if balanced properly, adds no vibration. A lot of weight can be removed from stock pistons with care. You MUST get the whole crank, rod, piston assembly dynamically balanced. In the UK, Basset Down know more about this that anyone else.
Ref cams, it all depends on how you want to ride it. I actually like the spitfire profile cams, they produce really good power between 4,000 and 7,000. E3134s produce more low end and less top end. A good compromise, and considered the best all round fast road cams by many, are Norman Hyde's half race cams, they're kinda like E3134s but higher lift. Remember to carefully check valve to piston clearances when using none standard cams plus you may have to relieve the inside of the cases a little to allow room for the bigger lobes.
Getting compression ratio up on a Triumph can be a challenge with a stock head and stock pistons. A few US sellers offer nice forged pistons in various CR choices. Triples Rule offer very nice alloy barrels and forged pistons if yer wallet is fat enough.
You may also consider that with a little machining work, a Norton crank and rods fits into Triumph cases, if used with a T140 top end even the piston deck height lines up perfectly. Depending on the overbore size used this can give up to 840cc.
But thats perhaps a little hard core! If you over tune a pre unit, the cases will split through the drive side main bearing. This is easy to strengthen though and to add an oil seal to allow use of a dry belt. But with this strengthened, the timing side case will break through the cam bush holes!
My advice would be a well balanced 750, Hyde cams, good magneto, 32mm concentrics if you want a period look, 34mm mk11 carbs if you want better oomph, Mikuni carbs if you wanna be flash.
Here's one I built and raced for 3-4 years in BHR racing before replacing it with a Noursh powered racer and putting it on the road, 840cc and 74BHP at the rear wheel, not slow...
Lightweight Dresda made Manx lookalike frame but built around a unit motor proportions:
Carbs were 34mm smoothbores which added a little power and mid range. Morgo barrels with special sleeves to allow +60 T140 pistons + squished head (by Dresda) = nearly 11:1CR that ran fine on pump petrol:
Timing side shot of motor:
Theatrical front brake!
