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By Bulli
#98512
The last Week we had finally ended our vision of a 750cc engine for the usual RE 500 PreUnit. After spending a lot of time in thinking and getting special parts.... we now finished the project.
The engine should look like a normal PreUnit Bullet from the outside, but should have 750cc inside. As far as we know, nobody did that before having success....
Kolben_UT.jpg
Piston in down position
Kolben_UT.jpg (319.92 KiB) Viewed 3872 times
Kurbelwelle.jpg
Crankshaft
Kurbelwelle.jpg (1.27 MiB) Viewed 3872 times
And since yesterday in the evening:
RUNNING: https://www.youtube.com/watch?v=dVjR6yUKEUA
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By Adrian
#98518
The largest oversize Bullet engine I have heard of until now was the Tollgate Classics 720 engine. What size bore and stroke is this engine?

It will be interesting to know what the vibration is like, or how well the standard size main bearings cope - unless you have uprated these.

A.
User avatar
By Rushour
#98565
This looks very much like the Hitchcocks long stroke crank which will take the capacity to 570 cc - and even with the 87 mm piston this will only be 612 cc - I cannot see the room to go much bigger on the sleeve and crankcase mouth - please tell us all how you got this to 750 cc - love to know ...
By Daiwiskers
#98567
Nice job but the liner looks very thin

Just watched video ???
I was thinking that has gone way over the Sweet spot for a single now I know it has
Sorry not for me
User avatar
By Bulli
#98640
.... this engine has a stroke of 121mm.
Abstand_Welle_Hubzapfen.jpg
Abstand_Welle_Hubzapfen.jpg (1.52 MiB) Viewed 3467 times
KW_Wellendurchmesser.jpg
diameter crank
KW_Wellendurchmesser.jpg (796.33 KiB) Viewed 3467 times
and we realized a bore of 88mm
Zylinderdurchmesser.jpg
Zylinderdurchmesser.jpg (405.84 KiB) Viewed 3467 times

which makes exactly 736cc ...... we thought, we can call it 750 already..... 8-)

The thickness of the liner is now 2.7mm. But since you may go down to a liner thickness of at least 2mm and there are pistons with 88.5 an and least 89mm easy available, you may have a real maximum of 753 cc.
As you may see on the video, the vibs of the engine are not heavier (even less) as they are an on a standard engine. We had the engine running for about 15 minutes and smooth run it hot to check the complete oilsystem is working properly. Plus we wanted to retighten the crankhead nuts after the first run. The engine had a smooth idle gas and a good throttle responsiveness. Even better than we expected .... :)
:arrow: Since i don't have a Bullet with a broken engine.... and i don`t have time to just change a engine for testing purpose... or i don't want to build up a Bullet with sidecar (where such an engine would be useful) for myself..... this engine will stay good visible in my garage just to proof that it is possible to bulid a running Bullet engine with 750cc....! :mrgreen:

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