Author Topic: 750cc Bullet engine RUNNING (Read 2967 times)

Bulli · **on:** October 10, 2021, 12:35:08 pm

...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 · **Reply #1 on:** October 10, 2021, 02:19:48 pm

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 · **Reply #2 on:** October 10, 2021, 03:05:08 pm

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 · **Reply #3 on:** October 10, 2021, 04:03:16 pm

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 · **Reply #4 on:** October 10, 2021, 04:26:38 pm

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

AzCal Retred · **Reply #5 on:** October 10, 2021, 04:41:20 pm

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 · **Reply #6 on:** October 10, 2021, 05:54:01 pm

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 · **Reply #7 on:** October 10, 2021, 06:55:52 pm

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 · **Reply #8 on:** October 10, 2021, 07:00:06 pm

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 · **Reply #9 on:** October 10, 2021, 07:04:52 pm

Quote from: Adrian II on October 10, 2021, 07:00:06 pm

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 · **Reply #10 on:** October 10, 2021, 07:38:19 pm

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 · **Reply #11 on:** October 10, 2021, 07:43:41 pm

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

Pierric · **Reply #12 on:** October 10, 2021, 08:35:13 pm

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 · **Reply #13 on:** October 10, 2021, 10:35:27 pm

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 · **Reply #14 on:** October 11, 2021, 01:04:15 am

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.

cyrusb · **Reply #15 on:** October 11, 2021, 01:18:07 pm

V=Ah. In inches that cylinder 3.515 bore 4.74 stroke has a volume of 45.97 cubic inches. Allegedly.
Stock Bullet 3.318"bore 3.55" stroke has 30 cubic inches.
That is a 16 cubic inch difference..All done with stock castings? You can only go so far fiddling with rod lengths and wrist pin heights.
The details should be eye opening.

AzCal Retred · **Reply #16 on:** October 11, 2021, 05:28:41 pm

From the pictures of Bulli's motor you can clearly see that the distance from the conrod bearing to the crank centerline is approximately the same as the diameter of the piston. You have said it's a 500 motor, not a 350, so piston diameter is at least 84mm. You can also see that the rod wristpin can't be too far above the bottom of the cylinder skirt, as the piston casting is flaring out there.

It's clear that Bulli has done some real whittling here. Whether or not it's a good thing that the wristpin is getting mighty close to the cases and the rod angularity has increased has to be determined in practice. If the engine holds up within its recommended parameters, it's a winner.

Here's a picture of the H's 500 stroker. You can clearly see the crankpin is closer to the crank centerline. H's built that piece as a racing part, intended to spin up to make real HP. I'm not understanding the thick layer of skepticism evinced here. It's a great effort, it doesn't affect your paycheck, and Harry Ricardo had probably tried all this anyway back in 1910. Kudo's to Bulli for the effort. Now it's time to slap this engine in a chassis and do some road testing.

https://en.wikipedia.org/wiki/Harry_Ricardo

Nitrowing · **Reply #17 on:** October 11, 2021, 07:01:47 pm

Quote from: AzCal Retred on October 11, 2021, 05:28:41 pm

I'm not understanding the thick layer of skepticism evinced here. It's a great effort,

Same here. The guy is claiming the motor os going to pull 100mph, will fart gold sparkles and run on rainbow juice. He isn't offering to build these or convert yours.
Just enjoy what he's achieved and hope he deigns to give you more details.

nonfiction · **Reply #18 on:** October 12, 2021, 03:06:15 am

I say a big Thanks to the OP Bulli for posting this here. What a thing! I'd love to learn more about how this came to be, and how one of our newest forumfriends came to be the person who made it.

Please may we hear some more?

Bulli · **Reply #19 on:** October 21, 2021, 09:40:30 am

OK, folks.....
> there is NO distance plate under the cylinder.
> the engine looks like a normal 500cc engine from outside..!!!!
> the cylinder liner has a usual lenght, but has notches for the conrod going free
> the engine case had been modified to have the conrod going free
> the piston from Japan is giving a compression ratio about 6.5:1, what is plenty enough for a engine with that stroke.....

> the liner thickness is 2.7mm (at 88mm bore) which gives 736cc. If you go to the maximum you may bore + you can easily get a piston you will have 753cc, the liner thickness will be 2,2mm... still enough...!
In this case we also have put in thicker spindles for the cams and idler pinions.