Rebuilding "Baby"

It was around four years ago that I bought a rolling chassis which constituted the remains of a TT2 replica built in the early eighties. It was in a sorry state, being kept in a barn for the last 25 years or so. I never took a photo of the bike as it I bought it , -- far too upsetting on the eye !
It came to me from Paul Evans in Wales who originally built it. He campaigned it in the UK BOTT championship, also the IOM TT throughout the decade. The engine came out for it's annual rebuild one year and somehow went missing from the workshop !
Moving along some 25 years, Pauls financial commitments to his new venture (A fantastic diesel engine museum http://www.internalfire.com so have a look ! ) meant it finally had to go. I made a promise to him that it would be going to a good home and it WOULD see the track again. He was in tears as I drove it away in the back of the van. It was his "Baby" and that had always the bike's name.

The frame is a TT2 copy. One of a number made by Nigel Hill of Saxon Racing. Traditional bronze welded 531 using a gap on the top tubes to cater for belt covers if desired, and cross braces between the engine mounts. The swing arm is a Harris item which affords a wider rear tyre than standard if desired. After fitting it to my frame jig, it appears to have a one degree shallower head angle than the original Verlicchi but otherwise quite true to form. Also from an engineering viewpoint, I have to say, much better made.
Forks are 38mm originally for a Moto Guzzi. These particular ones afford P08 caliper fitment on 300mm Brembo discs. Yippee !!
Dymag 18" wheels, alloy tank and a Maxton Koni shock propping up the rear wheel. The idea is to use as much of the original chassis as is useable and practical.


Now for the promise I made to Paul.

Here in New Zealand, the Post classic rules dictate such that a 600cc twin slots very comfortably into the pre 82 Junior class. The competition being something called a TZ250 Yamaha and ZXR 400 Kawasaki's. I am told these are some form of motorcycle other than a Ducati, Is that possible !! Has anybody out there ever heard of them ?

I started on the the engine last week using some 750 cases as a starting point. Traditional 583cc bore/stroke. 41/35 valves using P grind cams.
The combustion shape is now machined to the later tri-spherical shape on the cnc lathe. My fixture bolts to the chuck on the cnc and lines up on the valve stem as a datum, so I machine the larger seat pockets at the same time as the corresponding radius in the head. Then switch to the other valve, and then bolt up another fixture to hold the head face out and skim the recess for the barrel together with the squish band, and the mid radius between the valves. I previously welded up the 14mm plug holes and now re-position them for 12mm to emerge a little further away from the valve seats. New seats are aluminium bronze, as are the guides. We all have a favourite and I have used this material for many years without a single issue. If it aint broke, don't fix it. Then spend a day at the bench porting them both out to match up to some 40mm Dellorto's. I guess that's the hard bit done.
Std rod's are drilled for a positive small end oil feed, then shot peened.

As our events are more of a six lap dash than a proper race, I have elected to miss out on the flywheel, generator, starter, sprag clutch etc and use a lightweight ni-cad battery and constant loss ignition.
I recently came across a Pazon ignition system packed away in a drawer so will try it on this engine. If it doesn't perform sufficiently then an Ignitech TCIP4 kit is on standby as an alternative.
The motor is fitted with my dry clutch kit driving a traditional 5 speed cluster, using a traditional chain thingy linked suprisingly to the traditional 18" rear wheel.

The build is taking place with what I have available at this moment. In view of this, I could certainly use some 80mm high comp forged pistons to suit the later shaped heads if anyone has some unallocated.

Hello, congratulations on your bike is much attention to detail, I have not figured out if you've done the dry clutch is your project using a crankcase original side?

I saw that you have the fusion of the spider wire tightener clutch.

Excuse my English, I use a tradhuttore simultaneously.

Carlo from Italy.

Hi Glyn,
nice work I see.
Is that your handy work on the clutch assembly? Or is that as it was?
How is life down in NZed? Nice, quiet & peaceful? You have some nice roads up north.
Take care and hope you visit Aus soon. bring a big suitcase with you with some of your goodies!
Cheers,
Steve

Hello Glyn.

It will be fun to watch this one rise from the ashes. Your clutch cover kit looks better on an engine than in parts (the photos on your site). I'll bet is will be tough to find 80mm pistons with tops to match your chambers. Every one I've seen is designed for the old round hemi chambers. Red Fox (Jan) may have something that will work; see photo. MikeV

The dry clutch is using an outer casing of my own design. The pattern was formed by sawing a pantah cover up for the front bit and a 916 cover for the back bit. Then some welding, filing, polishing and a bit of good fortune. This was then used by the pattern makers to pour a mould of it from resin. Next cut the resin into six bits, and glue them together again a little further apart. This allows for the shrinkage in the casting process so it fits the crankcase rather than being finished fractionally below size. An awful lot of work and something that always passes without notice. The few pattern makers who are left are the unsung heroes, skilled artists from a fast disappearing era.

I also make the rest of it (even the black anodised oil window as I hate the old milky plastic ones). The plates are the latest oem Ducati alloy thingy's.

Hi Mike, The piston's look as if they are for the later head but the smaller valves. I have some 620 std road pistons in at the moment. They have a bump on the top and The compression checks out at 10.7/1, but am nervous about the combination of prolonged revs and cast pistons. I would be very happy with something for the older heads and plenty of material to machine so I can alter them.

The heads are now in place and the cam timing done. Squish is 0.9mm. Valve to piston clearance is now 2.5mm after machining a further 1.2 mm from the piston pockets. Valve timing is set for peak inlet at 106 deg atdc. The exhaust timing is simply a consequence of the inlet timing which I feel is way more important. SOHC, you can't have it all !!
It's all just a good guess at this stage but having the inlet advanced to 106 degrees should offer more top end power which the P grind cam profile also appears to support.

A couple more pics of the finished engine posted. Now for the rest of it. Can't wait !!

I like that ignition pickup.
Bill

I thought about stock modern 620 pistons as a possible quick solution (NOT stock modern 600), but aren't they for the 61.5mm crank (61.5 x 80mm = 618cc) Glyn? So, wouldn't they end up about 1.75mm too low once installed on a 58mm crank (61.5 - 58mm / 2) ? MikeV

Well spotted Mike, The 620 pistons do indeed sit low in the barrels when hung on the end of a 600 crank. The great god of plasticine told me to remove 1.2mm from the base of the barrels to achieve the 0.9mm squish without using a base gasket.

Has any one else raced with the stock 620 pistons ? Are they safe to use beyond 10,000rpm or am I heading for a big bang engine ?

It seems I may have helped stir something over here. A few others are dragging stuff out from their sheds and building Pantah's and tt2's to compete in the same pre82 junior class. Maybe with enough interest we can create a smaller race within a race ?

Due to there being 24 hours in each day, things have since moved on quite a bit.
Baby now looks 90% finished so only another 50% to go.

That 10h30 or 22h30 Glyn ?

and are your cases vapour-blasted ?



......nice Dymags by the way


salut;

Dick