twin engine crank behaviour. 9

[ivanheow]

hello to the collective ,

i am constructing a twin engined 1940's type racer . the 2 engines are straight 6 jaguar lumps, aluminium block 4 litre 245 bhp engines . i am tentatively designing them thus ..

gearbox/clutch/flywheel unit(remote).........10" prop........uj mounted to crank end .....engine.........crank snout to 400 lb/ft jurid donut.............crank end......engine.....snout with stock crank pulley harmonic balancer .


so , i have gone from a trq converter on the end of each crank ,to a prop to a flywheel on one ,and a jurid donut on the other .and from a damper on each to a damper on one .
these engines tend to run very smoothly ,and have good balance as stock .

in the past i have converted a c4 auto to clutch ,created 2 gearboxes back to back ,and the fastest turbo minis use my bespoke clutch design .so have a little transmission experience , but not much on harmonics and acrrued vibration re no flywheel.


thoughts?

regards
robert

http://www.youtube.com/user/legrandphromage

 

[ivymike]

I would suggest that you either
1) copy (precisely) a known-successful design
2) have a torsional vibration analysis done

 

[BigClive]

Where did you get aluminium block Jag sixes?

 

[MikeHalloran]

The typical crank snout connection is good for ~75 HP.
After you break a few, you will need a special crank on the 'rear' engine, with two drive ends, modified timing cover, etc.
... and that will affect your torsional analysis, too.

It would be easier and cheaper to just snag a Jaguar v12 from a wrecking yard...



Mike Halloran
Pembroke Pines, FL, USA

 

[ivanheow]

ivymike, there are no designs of this engine combination ...im a pioneer .;-)

bigclive ,from the scrap yard .

mike ,do you have any pictures of the ones you have snapped?


thanks chaps
robert

http://www.youtube.com/user/legrandphromage

 

[ivymike]

it's not something to be undertaken lightly... a simpler configuration to execute without extensive study might be to drive one set of wheels from one engine and the other set from another, via separate transmissions?

it's not impossible to connect engines nose-to-tail for increased power, see the Caterpillar 3524 here:

http://www.tetralab.ru/pages/viewpage.action?pageId=59473924

it's a pair of 3512 engines (each a V12) connected nose-to-tail.

 

[ivanheow]

hi mike , thank you for that picture .
the concept has been used many times in the 60's for drag racing ,and other one offs , there is a well known rod with 2 500 bhp small block chevies connected tail to snout .

http://www.hotrod.com/featuredvehicles/hrdp_0909_custom_speed_buggy/viewall.html

so im not worried about the connection , only about the vibration creating and handling situation .and wonddred if anyone on here would have any real world practical experience of doupbling up engines , or running 6 cylinder cranks with no damper or flywheel.

regards
robert

http://www.youtube.com/user/legrandphromage

 

[ivymike]

running an engine without a flywheel is probably in many cases better for the crank (meaning lower stress) than running with a flywheel...but that doesn't mean much w/r/t running a pair of cranks in series with a flywheel at the very end.

I certainly wouldn't go about it without either analysis and/or measurements...and I wouldn't stand too close during measurements if that route is taken alone.

 

[tbuelna]

The 4.0L AJ6 engine was a "stroker", and thus had an under-square bore/stroke ratio. Most I6 cranks also have 6 rod journals and 7 mains, which gives them a very long length. The combination of these two factors means the AJ6 cranks likely have low torsional stiffness. I can imagine all sorts of shaft dynamic issues popping up from coupling two of these cranks in series. For example, consider that when the no.1 cylinder of the forward engine fires, the applied torsional moment is transferred through 11 rod journals and 13 main journals on its way to the engine PTO.

MikeHalloran's proposal to make a dedicated crank for the aft engine with a stronger snout seems like a good start. You can have a custom billet crank made for a few thousand dollars, and it would be cheaper than replacing the rear crank on a regular basis. A torsional vibration study would also be a good idea, but it would be beyond the technical capabilities of most people.

Good luck with your project!
Terry

 

[GregLocock]

I'm gently wondering why the average crankshaft has a 6 bolt fastening to the flywheel on a 4" (WAG) PCD if they could get away with a little key and a single bolt. ie what Mike said. I have worked on a project to siamese two engines, to resolve the TV issue we ran them back to back and took the drive off the middle.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[MikeHalloran]

Thank you for the link to Yannick Sire's Speed Buggy.
It must be great fun to hoon around in.

Of course, a flyweight car like that with street tires couldn't develop enough tractive effort to actually require 900 HP, so the cranks and the coupler are in no great danger. ... and the cranks are modern SBC parts.

I'd like to amend my position. A custom rear crank with a sturdy nose is a waste of your money, because if it's anything like the stock Jag crank, and even if it's not, it will still break in short order. ... not necessarily from transmitting the power from the front engine, but from all the torsion waves traveling and interacting within it.

Crank dynamics are one major reason that nobody builds a straight-8 anymore. You're proposing to build a straight-12; it's a complete waste of your time, no matter where you put how many dampers, even if you learn enough about cranks to actually do a torsional analysis and select the exact right damper(s).



Mike Halloran
Pembroke Pines, FL, USA

 

[ivymike]

nobody builds a straight-8 anymore

at least not one that would fit in a car.

 

[MikeHalloran]

Ivymike is correct.
ISTR there are ship engines with ~13 cylinders in a row.
... but they redline at ~90 rpm.



Mike Halloran
Pembroke Pines, FL, USA

 

[pontiacjack]

This sort of thing happens every year on the first of April...

 

[BigClive]

Ivan - sorry - I was assuming that you were going to use the older XK variety of Jag 6. If you are building a '40s fantasy racer type of car the XK engine is far "prettier" and more in keeping with the '40s theme than the AJ Jag engine. The XK engine with polished cam covers, polished triple 2 inch SU's and manifolds etc. looks quite magnificent. Two XK engines in a row would be quite spectacular with six 2 inch SU's etc.
But I think your idea would have to be restricted to being just a "show" car - a car with a seven-foot long "engine" doesn't sound very practical.

 

[ivanheow]

your right clive ,

those early engines do look better .

these will run on throttle bodies with 12 bellmouths and tubular exhausts , the car will be called medusa(obviously) ... its combined engine length wil be 60 inches plus coupling .


regards
robert

http://www.youtube.com/user/legrandphromage

 

[ivanheow]

thans for all the comments chaps.

some other factors to be considered are , a top mounted roots type blower driven off the crank can use a considerable amount of power ,this ot only stresses the crank snout ,it also pulls it sideways , the pully is usully connected with 1 exta keyway . i plan on a 220 lbs/ft input ,and use several keys .

re crank vibration ... if i use a damper on the front engine ,and a damper on the rear of the back engine ,and the 2 cranks are connected by a vibration absorbing flexible rubber donut ,and neither crank has a directly mounted flywheel ....who knows , it may survive .max rpm is 5500. bearing in mind the engines cost 40 quid ,a lost crank is not a major disaster.

rethe multi bolt fastening of the flywheel , maybe to do with the size and weight of the flywheel itself? if you look at the shaft into an automatic gearbox , like the one i joined to the 1st motion shaft on a manual box to create a 350 lbs/ft clutched automatic , they are only around 15mm in diameter .

another factor is that the tyres on the vehicle will be narrow 7.50 x 16 ,so will not put a huge load on the engine ,and the vehicle itself will weigh around a ton .

http://www.youtube.com/user/legrandphromage

 

[ivymike]

a lost crank is not a major disaster.

As long as nobody catches the shrapnel, I suppose

 

[GregLocock]

So without being rude, you've come here, asked our advice, and decided to ignore it. Thanks for that.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[pontiacjack]

More advice to ignore: "... several keys..." doesn't leave much crank in-between the keys.