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Thanks for the support and advice guys! Bent thanks especially for relating your practical experience.

Connection to the rear engine with regards to the strength of the joint on the crank snout is something I've been considering abd researching.

I have read about different methods to strengthen the connection, and most likely what I'm going to do is cut a second key slot 180 from the stock (and cut the stock slot to full length if its only a woodruff key).

one of the advantages of the driveshaft coupler method, is that the rubber would damp the power pulses from the front engine into the rear engine crank snout, and I think that would help minimize the risk of damaging the rear crank snout. leaving the engine power output stock is another method of mitigating damage to the rear engine crank.

RX, the weak point is the joint between the two engines, specifically the joint to the rear engine crank snout, since it was never designed for this application. that joint sees the power pulse of each of the front engine's cylinders cyclically, and needs to be able to absorb the that power without damage. the guibo rubber would spread the jolt of each of those power pulses out over time, (making the power pulse more of a sine wave, than square, understand how?) thus attenuating the shock to the joint on the rear crank snout.

the more we talk this out, the better I'm liking the driveshaft coupler idea.

Bent, your suggestion about using a builck straight 8 block is ice, but far beyond what I could fabricate on my own (which is definitely a key component of this project) and would definitely be cost prohibitive (welding the aluminum heads, custom made straight-8 camshafts, etc).

I understand that this idea is a huge experiement, no matter that its been done before, and there's no guarantee that I'll have initial success.

I think I may try to talk directly to Yannick Sire...

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.

i personally believe the weak link is the front damper on the rear engine, one woodruff key is just not enough to handle the torque, if the rear engine looses fire, the front engine will probably shear the key or explode the damper, this may also happen under torque reversal, this can be helped by drilling two more holes down the joint between the crank and pulley then installing tool steel round bar in the holes, press fit of course.

fireing order, back in the day i experimented with twin engined triumphs, if you ran the two engines timed the same, very dificult, then the coupling would last longer than if you moved the timing apart.

if you moved the timing apart, then they appeared to make more power, faster e.t.

as far as the greek coupler, i have used these on dragsters, they can be run with a little offset, they can also be made using transmission parts

to align the engines, drop the cranks out of both engines and get a pipe turned down to fit in the main bearings, mount both engines on the pipe and then build your mounts to suit, if you are not solid mounting the engines, then see if you can, in addition to the pipe in mains, use a thick steel plate bolted to both pan rails on both blocks.

what about two blower pulleys, with a small diameter belt the same diameter as the pulleys but twice as wide to join them together, nose to tail.

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Emerson Fittipaldi did this early in his motorsports career. He and brothers built a 3200 cc Beetle. I remember seeing it in a picture going down a straight so fast the doors was sucked open several inches at the top and bottom. They welded the cranks together and it only survived a short while…

I remember a straight eight in a Pontiac or Buick "Service Wagon" my grandparents had. It ran so smooth, the valve cover was a reasonable place to put a cup of coffee while I looked at it.

You do get extra credit if you can make this out of air cooled VW engine halfs. Especially the other halfs from Justin's project.

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No. As long as it's 8 individual firings the torque peaks won't change.

I have been trying to post a picture for a few days, not sure if it's the site or my system but at work now anyway. As the rear crank's nose probably won't allow this (thin, hollow and a weakening thread cut up it) I would strongly consider running a jackshaft up the side ..

But if you are going to use a rubber coupling then I suggest you look at Alfa Romeo Alfetta parts, this is the front flywheel coupling, note it uses a floating spigot in a bush to centralise/stabilise the unit, you should be very interested in that (note there is more than one type) ..



...the spigot sits inside a bush that's a part of the flywheel and the 3 empty bolt holes are the drive studs from the flywheel, also a part of the flywheel but there's no reason you couldn't make your own drive unit based on that.

John, RE:keyed coupling, in my previous reply, I mentioend cutting the woodruff slot to full length and adding another 180 out, although, that method you mention - drilling down the intersection of the crank snout and front pulley collar and then driving in rod - I had read about in one of the many threads I found talking about coupling dragster engines. that method has the advantage of being something I could absolutely fabricate in my graj shop. also, having rounded profiles for the key grooves along the crank snout eliminates the stress risers - and possible source of cracks - that would exist in the sharp-ish corners of a square profile key groove.

I plan to time the engines in the configuration called "four-four" (ever read a copy of Audels Automobile Guidebook? I recently aquired a 1939 edition - fascinating!) which simply means the two groups of four cylinders are timed 90 degrees from each other. So, I'll set the two engines 90 deg apart.

I like your method of aligning the blocks by registering on the main bearing journals. about the very fiorst ting I'll do, (after disassembling the two engines) is build the common mount for the engines that will serve as both the test stand and the engine mount subframe in Bloody Hell.

I would have to say that right now, the engines will be joined via the driveshaft coupler method, and the rear crank snout drilled for 3 press fit rods as keying.

Cheap, I like the view of the alfetta parts. they might be a little hard to source outside of Ebay. most likely it''ll wind up with a BMW piece scrounged from Henry's Used Auto Parts, though I'll replace the rubber with new - you can even get these neat repklacements that have an alloy center "disc" with urethane inserts



as far as a jackshaft along the sies of the engines, this introduces a couple orders of magnitude more complexity, which = $$ and time. the simplest route is coupling the engines inline, and overbuilding the coupler joint somewhat.

EDIT: here's a video showing the construction of the modified driveshaft coupler used to join the two SBCs in the Sire Customs Priapism v-16 hot rod/custom.

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The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.

Alfa parts are very common, more so than you think but it's a community thing more than a public one. Join a forum or community and you will have excellent access.


But anyway, no jackshafts really are easy.

Keyways don't need much area but they do need to be an interference fit, once/if they get loose you key will last 2 minutes before it shears, so interference and appropriate locktite. If there's room then ultimately a taper and keyway is best hands down.

Cheapracer I know nothing about Alfettas, but is that a torque tube for a rear tranny?

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I can explain it to you,
but I can't understand it for you.

engineering wise, Cheaps jack shaft idea is probably the best.

the rubber dohnut will be fine if you can get the two motors in line, this system is used on many cars from ford to mecedes for drive shaft couplings.

look at some formula cars and lotus elans at the rear axle, this type of rubber coupling will happily run out of line all day and is deigned to flex as the axles go up and down.

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this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

No, they don't have a torque tube.

The tailshaft is permanent fixture to the engine's flywheel (via a spider), has a centre donut, spider and spigot assembly and a third spider, spigot and donut at the front of the clutch housing attached to the front of the rear transaxle (2 tailshafts). I know it well as I had an Alfetta for 7 years.

By the way, the 2 entire tailshafts, all the joints and 2 flywheels (engine and inside clutch housing) spin at all times in unison with engine.

mm, maybe. there's a whole truckload of engineering challenges to solve to make it work. how and where do you mount the shaft, sourcing the shaft itself, length of the chains, sprocket sizes, tensioning the chains, maintaining chain alignment, lubricating the chains (I've ridden motorcycles for 39 years, trust me, I've paid my dues on that pain in the ass chore. not inclined to design it in), where and how to you mount the clutch, get power to/from it, actuating the clutch, I'm leaving some stuff off the list, but all of it will need custom fabrication...

I won't say that the longitudinal jackshaft idea hasn't seemed viable when considering a different application (because I've actually thought it might be the way to go for coupling four HF Predator 212 small gas engines in a scaled up Cyclekart) , but for this application in intriduces more complexity than is necessary.



yeah, they are certainly a proven technology. I don't think aligning the engines will be all that hard, as long as I do my due dilligence on the initial mounting and then provide some adjustability to finalize the alignment. I'm not saying it'll be cake, but shouldn't be too hard. I can already see the way forward.

_________________
The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.

Hi had you thought of using a standard axel cv joint, from some fwd front hub assembly, you could have a spine cut onto the outside of the nose of the rear crank and if its a hollow nose have a piece of bar pressed in to the crank to fill the hollow,then slip the cv onto that, the same way it attaches to an axel, and on the other side on the rear of the front engine have a female spline either in a flange, or machined into the centre of the flywheel to slip the cv spline male end into, the male spline on the cv could be shortened to save space and alignment will never be a problem as the cv will even work with a misalignment of some 3-4 degrees. and a cv will transfer a lot of power no problem.
Another way of doing it is to reverse the above, and have a spline cut inside the hollow nose on the second crank, and push the male spline of the cv into it, and then mount a flange with a short piece of old axel with spline on the flywheel of the first engine to insert into the rear of the cv, or just cut a female spline in the centre of the flywheel or rear of the front crank, and use an old axel spline to join from the flywheel/crank to the back of the cv.
I have been thinking of building a project with either twin v8 or twin bmw m70 v12's and this is what I came up with for joining them together, I would be interested in every ones thoughts good or bad.

Countach,

mis alignment is still your problem, the cv joint will account for an angular misalignment but an axial alignment problem will require two cv and as a consiquence will space the motors too far apart.

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this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

Robb,

the problem with aligning the engines in a street application is the flex in rubber motor mounts as you can't guarantee that they will flex in unison and by the same amount, i would suggest the newer hydraulic type of mounts positioning them at the "roll center" of the engines and as far out as possible as the constant amount of "lift/squash" in a mount will mean that the engine will move less the further away from the crank the mount in located

as far as the difference in timing the pair, with a six bolt coupling, you have six choices, if you choose a different pattern for the fixing to the rear engine crank then you may be able to divide this into 30 degree increments by having four bolt fixing, in reality, there are only two choices, parallel or 90 degrees out of phase, i would suggest that you facillitate both positions.

on a slightly different note, have you ever looked at boat motors and how they are coupled to the out drive, they use either a rubber coupling that bolts to the flywheel with the crank bolts (mercruiser) or they are a triangular plate that bolts to the flywheel (volvo penta) with splines inside both units.

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

John I agree about the engine alignment issue, and that's why I had thought to hard-mount the two engines on a separate frame, making it easier to maintain alignment, and the mouting that engine subassembly in the car frame on isolators of some sort.

I had not looked at the marine splined couplers, didn't even know such things existed, thanks for the info.

turns out though, after an evening of pictorial research, the VW ABA engine may not be suitable for this application, and here's why.

on the VW ABA engine, about .5 crank snout protrudes from the front oil seal.

on the picture shown, that rusty-looking are at the very end of the crank snout is what sticks out of the ABA oil seal flange. behind that red area, the thin dulled line is the mark made by the front oil seal.



in place, with the oil seal flange assembled, it looks like this:

(AEG engine shown, ABA is fundamantally the same)



It so happens, that given the short length of crankshaft engagement, sometimes the timing sprocket can experience a failure and damage the the short key slot. The fix is to drill the crank end for insertion of a dowel pin (sometimes two) thru the sprocket and into the crank snout.



while, by all reports I found, this is an acceptable method of securing the timing sprocket to the crank, its not nearly enough engagement (even if I drill for 3 pins) to make me confident coupling to the ABA crank snout.

So, Plan B... which actually was Plan A when this straight-8 idea started forming in my head.

While I am something of a Volkswagen Man (having owned more Vdubs than any other car make) , I am also a Suzuki Man, having owned more suzuki motorcycles than any other make... it's just the way it has turned out, not any special kind of brand loyalty...

...anyway, as part of another idea - resurrecting my old SuZuki GT750 water buffalo by replacing the worn-out 2-stroke triple with a Suzi 3-banger G10 four stroke - I became familiar with the Suzuki G-series engines and thought the G16 (1598cc four) would make a reasonable candidate, and, again with some pictorial research, so does it seem.



Shown above is the G16 crank snout, which has a nice full length key slot, and engages the timing pulley for much more deeply than the VW ABA or AEG. Further...

...the G16 timing pulley (which is what my coupler will be attaching to - and would have attached to on the ABA) is tapped and threaded for 5 bolts (the VW ABA has only 4)



as can also be seen, the G16 has room around the snout and timing gear for other key slotting, including the press-fit-dowel interface talked about upthread.

the G16 has another advantage over the ABA in that its an all-aluminum engine (the ABA has a cast iron block and ally head). Like the ABA, its well represented in the boneyards so its fairly easy to find good examples of the SOHC 16-valve version. I know I'm losing some displacement and a bit of power, but ultimate power isn't the focus.

swapping to the G16 also solves the issue of connecting to the transmission (I'd thoguht of connecting the ABA to a porsche 944 or 924 transaxle, that would be kinda kewl) but by the simple expedient of using the 5 speed out of a a samurai or Geo tracker, and even including the rear axle from one of those donors, my driveline is pretty much solved - at quite possibly the least expense - with factory parts.

_________________
The B-3 build log: http://www.locostusa.com/forums/viewtopic.php?f=36&t=13941 unfortunately, all the pictures were lost in the massive server crash

The beginnings of the Jag Special,
https://www.locostusa.com/forums/viewtopic.php?f=36&t=19012
Again, all pictures were lost.