[Bulli]

...we have built a perfectly running engine to be used in a regular PreUnit RE Bullet frame. There is nothing to see from outside. But inside you will find WOW It has a stroke of 120mm and a bore of 88/89mm giving 730 - 755cc cylinder capacity. See it running: https://www.youtube.com/watch?v=dVjR6yUKEUA
We had been running it for about 15 minutes, checked the oilsystem und everything else... untill it had been getting really hot. It ran absolutly perfect. So the first running-in had been done now. After cooling down, we thigtend the cylinderhead nuts again with the recommend torque.
I will now put this oneandonly750cc-Bullet-Engine in my garage or livingroom..... because i dont`t have a bullet with a broken engine to test the engine furthermore.... this engine is perfect to be used in a sidecar-bullet anyway, because it is not good for rpm over 3.500/3.750 after completely runnig in ...... but has very much power from low rpms on. And i don't like sidecars...

[cyrusb]

Wow,
 Thats an awful amount of time and treasure to just let it sit in the garage.
  Why are there 2 bore dimensions, creating 2 displacements? Typos?
  How do you adjust the cylinder height which now needs to be 30mm taller? Spacers? Custom cylinder?
  Also, a cheap box fan goes a long way when cooling a running engine in the shop .

[Adrian II]

With the extra low-down power that engine ought to produce, you could probably raise the gearing enough to compensate for use in a solo motorcycle and still keep the engine speed within your 3750 RPM limit.

A.

[cyrusb]

Actually the cylinder has to be 15mm taller. But even that is quite a distance  .596". My mistake.
 Still would like more details, everything looks so stock.

[Karl Childers]

I can give it a good temporary home until you find a bike to put it in.

[AzCal Retred]

Send it to Karl - I have a spare 700 Twin frame, fork & wheels and a partial 4 speed transmission for such a project I can get over to him. Karl has a nice shop & looks to be robust enough to kickstart such a beast! The Boyer Mk4 ignition from my ES350 will slap right on and prevent backfires from pulverizing your leg/knee.
I propose the 4 speed with the Hitchcock's Trials gearing mod, as it gives a very wide spread between 1st & 4th. The first 3 gears are unaffected and so make low speed operation easier as the power pulses are closer together. A 750cc could easily handle the "jump" from 3rd to 4th.
Box it up, sounds fun - ACR -

[AzCal Retred]

This mod provides a wider overall ratio than even the fabulous 5 speed. A 750cc engine could pull the big 3rd to 4th jump. Let's get that engine a home!
I assume a roller big end, so the high volume pumps could be employed to good advantage. At 15mm taller, the frame backbone may need "adjustment". The iron barrel may be adequate for testing, but an alloy unit seems a better fit for significant real world use. Let's find out, shall we?

WIDE RATIO GEAR SET - TRIALS GEARS, (2 gears) 4 SPEED
PART No. 90024  £93.50
<< Suitable for all Indian made 4-speed 350cc and 500cc Bullets. This pair of gears lowers the 1st, 2nd and 3rd ratios, keeping 4th gear the same.
This is ideal for green lane use, giving the benefit of low gearing, yet keeping a high top gear for the road.
Standard ratios:
1st = 2.78:1
2nd = 1.84:1
3rd = 1.36:1
4th = 1.00:1
To:
New ratios:
1st = 3.19:1
2nd = 1.97:1
3rd = 1.46:1
4th = 1.00:1

[cyrusb]

By my count (and I may be wrong) the cylinder seems to be the stock height by fin count, and I don't see any stroker plates.
 Or, we may have something as rare as the infamous Webly-Vickers 50-80 mill.

[Adrian II]

Quite, has Bulli actually mentioned that the engine is taller? Yes, it has a long stroke custom crankshaft, but that doesn't look like a stock con-rod to me. In fact it looks like the steel con-rod from an Electra-X has been used, these are shorter than the original iron barrel alloy rod and might allow for the barrel height to be kept stock.

A precedent - Hitchcock's long stroke crank for the 535 CGT uses a shorter rod so that you don't have to fart around with barrel spacers and over-length push rods and cylinder studs.

A.

[cyrusb]

Quite, has Bulli actually mentioned that the engine is taller? Yes, it has a long stroke custom crankshaft, but that doesn't look like a stock con-rod to me. In fact it looks like the steel con-rod from an Electra-X has been used, these are shorter than the original iron barrel alloy rod and might allow for the barrel height to be kept stock.

A precedent - Hitchcock's long stroke crank for the 535 CGT uses a shorter rod so that you don't have to fart around with barrel spacers and over-length push rods and cylinder studs.

A.

Well of course, but that is only a 35cc gain.
 Bulli is claiming a 250cc gain. The math doesn't add up with a short rod.
 Ooops forgot to mention, that gain varies from 730cc to 755cc's.

[AzCal Retred]

Cyrus declared it was taller, I just assumed. The UCE piston looks about 1 centimeter or 1/2" shorter than the normal Pre-Unit slug. A "short rod" & UCE slipper piston may have done the trick of making a 120mm stroke fit in a stock cylinder. At a 120mm stroke, that's 17mm longer than the Hitchcock's 103mm unit, or about 8.5 mm more "lift" than the H's unit.  A final CR of 6:1 would still be good enough for a near 750cc tractor engine. I'd certainly like to see it in a running machine, it'd give a Panther a run for its money, eh?.

[cyrusb]

Its hard to increase the displacement without actually increasing the displacement.
 Lets wait and hear from the poster about his methods...

[Pierric]

Isn't the 500cc -more or less - a 350cc fitted with a big bore kit ? I read that it was the reason for it to be more vibration prone and less balanced that the almost immortal 350 engine which has endured so much in rough indian conditions for 50 years.

Would a 750cc kit be actually usable (apart some short suicide run on a fast track just for the heck of it) ?

[Adrian II]

Apart from the 500 crankcase mouth being bored out for the larger diameter cylinder liner and the different cylinder stud spacing, the 500 cases have strengthening webs for better main bearing housing support, I'm not sure about what the 350s have, though.

However, giving the crankcases too much stress can have consequences. I had to return a set of used 500 crankcases I bought Hitchcocks' when I discovered this - it turns out these had been used in one of their MX bikes.



You can beef things up on the timing side with a NU2205 bearing instead of the NU205, the bore for the bearing needs to go 3mm deeper as the bearing has 3mm longer rollers for better crankshaft support, though the inside and outside diameter of the bearing is the same as the NU205.



You will have noticed that with the mod the bearing outer will now block off the oilway from just below the end of the cylinder liner, a little dremel work is needed.



Bulli might already have uprated the bearings, hopefully he will give us some more information about those too.

A.

 

[AzCal Retred]

Bulli says the stroke is 120mm, bore is about 88mm, so a approximately a 133% increase in displacement from the 90mm x 87mm 535.

120/90 = 4/3 = 1.333

535 x 1.333 = 713ish, and an 88-89mm bore I'm sure gets you in the neighborhood of 735. That's just math. An 89mm piston is just slightly larger (2%)  than the 87mm of the 535. Sounds doable if you aren't spinning up the motor.

Bulli clearly says this is a low speed motor, 3,500 RPM or so, not an MX machine. It is more analogous to the old Panther sidehack rigs, a big torque generator. You can get away with a lot at low RPM, inertial loading at 3000 RPM is very low compared to the same engine turning 6000 RPM.

If it's relatively smooth at 2500 or so, it would be a good fit for a easy riding Bullet. With a wide ratio gearbox bolted on, it would be even better. Ace says repeatedly that the 103mm Hitchcocks crank would make a great sidehack rig. Bulli's 700+ cc torque monster would be even more suitable. A test rig will tell you how it survives in the real world.