02GF74
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| posted on 23/8/07 at 03:48 PM |
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thinking aloud - DIY v8 bike engine
Here is the idea - is it DIY dioable?
1. Take two 4 cylinder bike angines, let's say 750 cc to get lower car tax.
2. remove the lower part of the casing and using metal plates, somehow stick them side by side.
3. get a couple of gears e.g. old car geabox and stick same size gear onto each shaft. One engine is rotating in other direction so the gears will
turn right way.
4. attach another gear to one engine so that is truns another gear in ration 2:1 (gives car gearing.
5. fit a car fly wheel to the dear and mate to car gear box.
6. Make sump and sort out oil system.
So how feasible is this for a DIYer with a drill press, welder and hammers of verious sizes?
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worX
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| posted on 23/8/07 at 03:51 PM |
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It all depends on the Hammers of various sizes in my opinion!!! 
Steve
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novacaine
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| posted on 23/8/07 at 03:53 PM |
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you make it sound so easy, i might have a go at making one this afternoon and ill test it tomorrow 
flat would be easier but in either case would require custom crankshaft and possibly custom con rods, but after that i suppose your ok, i seem to
remeber a story of a V8 hayabusa lurking somewhere in the depths of the internet
And you run and you run to catch up with the sun but its sinking, Racing around to come up behind you again, the sun is the same in a relative way but
your older, shorter of breath and one day closer to death
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Neil P
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| posted on 23/8/07 at 03:54 PM |
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It's a complex job, you'll probably need to invest in a file too!
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02GF74
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| posted on 23/8/07 at 04:04 PM |
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this is rather interesting.
I bet he had a saw too 
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MikeR
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| posted on 23/8/07 at 04:12 PM |
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you'll need gaffa tape, if you can't fix it with gaffa tape - you've not used enough.
with your idea you wouldn't need custom crank etcetera as they'd be side by side.
You'd probably be better using a plate thats shaped like /-\ with the engines mounted on the / and \. That way you will hopefully find the
inlet / outlet easier / not fouling.
The other problem is making something for the crank to run in and then something for the 'final' drive to run in.
Would it not be easier to take two bike engines, solidly mount them together then instead of a two flywheels do what you suggested. Same idea, just
perhaps a little less work.
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02GF74
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| posted on 23/8/07 at 04:17 PM |
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^^^ - yep -that is the idea - each bike is running using its original crank but the cranks are extended to fit on gears that run in opposite
directions.
The tricky bit is then getting the final drive, nothing a bit of sikalex can't fix.
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pewe
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| posted on 23/8/07 at 04:19 PM |
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Laverda tried a V6 in the late 70's/early 80's by strapping two 3 cyl. engines together.
Some pics on Youtube
Can't remember why but it never was that reliable.
Cheers, Pewe 
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arrybradbury
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| posted on 23/8/07 at 04:30 PM |
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Something like this....
http://www.springsspeedway.com/default,837.sm
Looks like a good final year project, i wonder if they'd let me do something like that
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matt_claydon
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| posted on 23/8/07 at 04:59 PM |
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Would be easier if you mount them inline and make a straight-8, guess you'd have problems fitting it into a seven though.
Whilst slightly more bizarre that your idea, this engine has three separate crankshafts joined with gears:
http://en.wikipedia.org/wiki/Delta_engine
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Peteff
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| posted on 23/8/07 at 05:00 PM |
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each bike is running using its original crank but the cranks are extended to fit on gears
If the cranks are both still used it will be a very wide engine and if the cylinders are inclined so the inlets don't foul it will put the
exhausts in the middle where you can't get at them. The gears that connect the cranks would be large as well unless you have a lot of small ones
or use chains to connect them. Use two Honda V4 750 engines joined together then half the work is already done for you
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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wheezy
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| posted on 23/8/07 at 05:10 PM |
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Radical have done something similar with there V8. Only they use a single crank case with 2 Hayabusa cylinder heads. The only thing you need to do is
design and build your own crankcase
Radical SR8
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ned
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| posted on 23/8/07 at 05:15 PM |
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If you're running the two engines with their existing cranks and just putting on what is effectively a transfer box it sounds as if all
you'd be doing a creating a twin engined car like tiger did years ago!!
Ned.
beware, I've got yellow skin
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MikeR
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| posted on 23/8/07 at 05:52 PM |
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just thought of something - if you run two engines side by side and transfer the motion to a middle third gear - isn't that gear going to be
turning the 'wrong' way.
You're going to need to either source a honda gearbox / rear diff or use engines that run the 'wrong' way for a
'standard' gearbox.
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mark chandler
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| posted on 23/8/07 at 06:26 PM |
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Arial square 4's used two cranks I believe.
What you are proposing does dilute some of the bec'ness as the multiplate clutch and keeps weight close to the centre, also I,m not sure if you
lose the clutch you may lose the balance of the crank.... as in it will self destruct.
Better idea which is proven is two complete bike engines and have two gearlevers.
If in line you can get away with a central shaft which both connect to, if opposing I suspose you could have a chain on one and cogs on the other.
Tools are not so much of an issue, more on what you are capable of.
I know cart racers that used to use say Yamaha cylinders and heads on honda blocks but these were always 2 stroke.
Regards Mark
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Dangle_kt
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| posted on 23/8/07 at 06:40 PM |
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two engines, a zip tie - DONE!
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smart51
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| posted on 23/8/07 at 07:03 PM |
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At the end of each crank on a bike engine is the primary reduction gear. The two cranks could mesh together using these, except that the exhaust from
one would point at the inlet of the other. One of them would be at the wrong angle too, so oiling would be tricky. and leaks, and extending the crank
for a car clutch might be difficult.
do 750s rev as high as 600s? I want an engine that sounds like an F1 V10. a 1.2 bike engined V8 would rev to 16,000 which is almost like an F1
engine.
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britishtrident
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| posted on 23/8/07 at 07:15 PM |
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Read up on the history of the 1966 H16 BRM engine guys --- if Tony Rudd couldn't make it work.
The other option of making the cylinder blocks share a crank dosen't work either 8 cylinder crankshafts are much bigger diameters than 4
cylinder cranks.
Same goes for the straight 8 option.
Where 4 and 8 (& 6) cylinder engines are built as families sharing common components the 8 cylinder is designed first.
The Lous Espirit V8 is the exception but but the Lotus 907 4 cylinder was based on a horrible rough running cast iron Vauxhall engine that was
designed to be half a V8.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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indykid
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| posted on 23/8/07 at 07:58 PM |
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quote:
Originally posted by Dangle_kt
two engines, a zip tie - DONE!
only if you use one of those really big ones like they use on planning notices
tom
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JoelP
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| posted on 23/8/07 at 08:35 PM |
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id be tempted to use just one standard crank for both engines, and cut each rod to half thickness so you could get two into the space of one. Then
'just' strengthen it to prevent them breaking.
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higgsti
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| posted on 23/8/07 at 09:12 PM |
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http://www.motorcyclistonline.com/features/v12_custom_kawasaki_2300cc/photo_04.html
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ironside
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| posted on 23/8/07 at 11:18 PM |
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There were 2.0 and 2.4 litre RST-V8 engines which were based on two bike engines and a shared crank.
Not very Locost I know but it sounded cool - 15k rpm, 74kg, 40 valve, quad cam and 340bhp.
The websites appear to have vanished, they were at http://www.rst-v8.com/ and http://www.rst-v8.co.uk/ but there is an archive copy from 2005
available here:
http://web.archive.org/web/20050104082101/http://www.rst-v8.co.uk/
It did happen, they put one in a Caterham SV (I know someone who drove it) and maybe an Elise too - I don't know what happened though -
I'm surprised the websites have gone.
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Angel Acevedo
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| posted on 23/8/07 at 11:59 PM |
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Deja Vue
Apparently all the topic was written today, but I clearly remember reading it before.....
Beware of what you wish.. for it may come true....
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akumabito
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| posted on 25/8/07 at 03:28 PM |
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...would it be an option to make a hybrid engine of sorts? Using a car V8 block, and filling it with bike pistons and rods? (using the original crank)
that way you could still have a high-reviing engine..
Mixing and matching parts would be a nightmare though..
Let's have a quick look...
Cheap(ish) V8 engines:
The RV8 = 88.90 x 71.12
BMW 3.0 = 84 x 67.6
BMW 4.0 = 89 x 80
Getting bike bits to match... Here's a list of some engine specs..
There are not many engines that have a bore in the 80's. At least not many listed on that list..
Let's see... a bore between 84 and 90...
Suzuki DRZ400
Buell Lightening
Buell Ulysses
Well, even though that list is far from complete, it doesn't ist many options anyways..
The Suk is right out, it's a single cilinder.. you'd need 8 of 'm...
The Buell's are better, but there aren't that many of those around.. besides, it's a useless V-twin.
Hmm... what else's out there (having a tediously slow connection doesn't help the search either!)
Honda Goldwing? Nope.. besides it not revving very high, it also got a measly 70s-something bore.
Ya know what.. I believe this is a bad idea. 
You'd still have the problems of mating the rods to the car crank, fixing the compression ratio, and if you thought of using the RV8,
you'd also need to figure out what to do with the ciylinder heads to flow enough air in...
Also; it would probably be fairly heavy, AND you'd lose the sequetial transmission.
*slams head against wall for even bringing up this idea*
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