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twin engine crank behaviour.

twin engine crank behaviour.

(OP)
ponderhello 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

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

Where did you get aluminium block Jag sixes?

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

(OP)


ivymike, there are no designs of this engine combination ...im a pioneer .winky smile

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

RE: twin engine crank behaviour.

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


RE: twin engine crank behaviour.

(OP)
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_c...


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

RE: twin engine crank behaviour.

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.

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

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: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

nobody builds a straight-8 anymore

at least not one that would fit in a car.

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

2
This sort of thing happens every year on the first of April...

RE: twin engine crank behaviour.

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.

RE: twin engine crank behaviour.

(OP)
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 smile.


regards
robert

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

RE: twin engine crank behaviour.

(OP)

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

RE: twin engine crank behaviour.

a lost crank is not a major disaster.

As long as nobody catches the shrapnel, I suppose

RE: twin engine crank behaviour.

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

RE: twin engine crank behaviour.

(OP)
thanks chaps ,

re the shrapnel , there will be substantial guardage around all exposed rotating bodies ,being impaled is never fun .

re ignoring advice , oh greg ,my little button , how wrong you are , i am taking it all on board ,and as you may have not noticed ,have added another crank damper ,solely due to this forums freindly warm ecourageing and adventurous input.


re the the keyways and the meat left betwen the root of the keyway slot ,and the threaded hole ,if you study the top fuel and other high 'supercharger bhp draw' engines out in the ionosphere,you csan see they seem to get away with it ,without launching snoutage .


it appears to be a case of , if its not bult , no one will know if it can work ,like so many of my projects , and edisons light bulb.
(the only difference of course is edison knew what he was doing )


regards
robert

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

RE: twin engine crank behaviour.

If you're referring to the stars, you'll notice they're next to posts by Pontiacjack{{/b] & [b]MikeHalloran. The stars are anonymously given by other members; and pertain particularly to the specific post where they appear, not to the thread in general...

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: twin engine crank behaviour.

re: top fuel cranks.
No Jaguar crank snout has dimensions as robust as a fueler's billet crank snout. "Normal" cranks must find a compromise between number of keyways and integrity of the resulting configuration.

RE: twin engine crank behaviour.

ivanheow-

The crank snout on most engines is not designed to transfer much torque. The damper/pulley commonly use an interference fit, and it's the friction from this interference fit that provides the primary torque transfer capability. The keyway is just there to provide indexing. At the crank/flywheel connection a similar situation exists. The clamping force of the bolts must be sufficient to transfer all of the crank torsional moments by friction, without any slippage at the joint face. At either joint, if there is even the slightest amount of relative motion at the contact faces there will be fretting damage, and surface fretting damage will create fracture initiation points.

Another important thing to consider is the design of the coupling. Even if the two engine blocks are rigidly connected, the crank coupling should allow for some angular misalignment/compliance during operation. If the coupling does not have sufficient compliance in bending it can easily produce enough deflection in the cranks to cause edge loading of the rear main bearing of the forward engine and the front main bearing of the rear engine.

Good luck.
Terry

RE: twin engine crank behaviour.

(OP)
2thumbsuphi terry ,

thank you for the input ,

it mirrors my thinking ,the usage or a drivelive gurid coupling is to take into account exactly what you refer too .

re the pulley , i think that i will make the new pulley an interferance fit ,and also, after a bit more research i am going to add one more 1/4'' keyway , this in addition to the 3/16th keyway ,matches the design used by engines using a large rootes blower and substantial bhp to drive it . in fact , i must get on with a full engine design computer model to see just what sort of bhp the large blowers consume . .

regards
robert

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

RE: twin engine crank behaviour.

I think the chain-wrapped-around-two-sprockets type of coupling would allow a bit of misalignment or movement.

RE: twin engine crank behaviour.

Chain couplings are available from several sources, capable of dealing with reasonable imperfections, etc.

They have one more virtue that may be of interest.
With the chain removed, there is room to sneak a poly-V belt through the resulting gap, so you don't have to remove the front engine to change the rear engine's accessory drive belt.

Mike Halloran
Pembroke Pines, FL, USA

RE: twin engine crank behaviour.

"The damper/pulley commonly use an interference fit, and it's the friction from this interference fit that provides the primary torque transfer capability."

Can't speak for modern V8s, but 60s and 70s Olds and Buick, unlike Chevy used slip fit dampers and big bolt torque to provide end clamping for the friction.
REd block Volvo 4 cylinders thru '95, early Miata, and 1996 Integra non-V-tec are also slip fit, high bolt torque.

RE: twin engine crank behaviour.

It seems to me that one way to engineer a high torque connection to the crank snout of the rear engine would be to go with splines. Obviously there would be some stress & materials analysis needed to determine an appropriate spline pattern, given the crank parent material & OD. No guarantees from yours truly that there is an adequate solution; I'm just speculating. I'm thinking of perhaps a companion flange splined onto the crank snout. Ideally an off-the-shelf companion flange, e.g. from a 3rd member would be selected as the mating component. Precision machining would be needed to modify the crank snout accordingly. Completely separate means for handling axial and angular misalignment would still be needed, as discussed above.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: twin engine crank behaviour.

I'm not picking on SireCustoms' interestingly engineered vehicle. I like it a lot.

At 0:11 it looks like the rear hub attaches to the rear engine using 3 bolts into the damper hub, and a lone bolt clamping the center of the damper, so he's likely back to the OEM attachment of the damper hub to the crank.

The centering stud that engages the "other" hub is common for those style couplings in driveshaft service, since radial stiffness and positioning is required. For reasonable radial misalignment tolerance between the engines I'd lose the stud, although that may be the least of his problems.

This entertaining video of excercising the vehicle a bit is supposedly from 2009.
http://www.youtube.com/watch?feature=fvwp&v=xq...

So it might be interesting to ask how the coupling, crank snout attachment, and shared stressedmember headers have been holding up.

RE: twin engine crank behaviour.

Quote (hemi)

It seems to me that one way to engineer a high torque connection to the crank snout of the rear engine would be to go with splines.

hemi- Good thought. I imagine it would be possible with most cranks to re-machine the snout with an external spline. The external spline would provide lots of options for attaching couplings. It would also be more economical to rework an existing crank than it would be to have a custom crank made. A spline joint at the snout would greatly benefit in terms of durability/wear from oil lubrication.

You would want to check the modified snout for adequate fatigue life. It would take a bit of work to determine the net torque profile produced at the front flywheel, but determining the rest of the inputs for the analysis should be fairly straightforward. Of course, unless you have fatigue properties for the crank material you would also have to make some assumptions about acceptable stress limits.

Regards,
Terry

RE: twin engine crank behaviour.

(OP)
hello tmoose ,

i have been in discussion with yannick sire ,on just that topic ,i asked did he use the locating pin ,and he sent me a link to that video .i am thinking along the same lines as you , with two engines in line and securely located , is that pin a help or an unnecssary encumberance,and a litle radial flex would work better?

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

RE: twin engine crank behaviour.

tbuelna, thanks for the feedback. My thinking is, if there is enough meat on the crank snout to allow for a spline pattern from a passenger vehicle sized transmission output or 3rd member input, you're into a pretty high torque capacity ballpark, considering first gear multiplication of engine torque, i.e. for a given spline design in its originally intended application behind the transmission. This would provide encouragement to go forward with the stress & fatigue analysis as you outlined. The big unknowns, other than the material properties, of course would be the dynamics resulting from the coupling of the two engines.

I see you must be considering a free floating joint, as on a slip yoke. That may well be a common off the shelf companion flange application. I suppose the companion flange could also be rigidly fixed to the crank snout, e.g. with a central bolt & corresponding features that constrain the axial location of the companion flange with respect to the crank. One other configuration that comes to mind is a tapered spline, assuming such a companion flange could be sourced. This would result in a press fit onto the crank, again retained by a fixing bolt. I have seen tapered splines applied to steering Pitman shafts; this may be commonplace but I don't know as I haven't examined very many steering boxes that closely.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: twin engine crank behaviour.

Quote (MikeHalloran)

A shrink disk could be fitted without machining the crank.
True, but I wonder about the torque capacityponder

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

RE: twin engine crank behaviour.

My instinct would be to get a slow taper machined (pref ground) on the rear engine crank nose with a custom corresponding internally tapered flange with lugs to take the donut coupling out of a hide grade steel in one. Sweat the flange onto the crank, you may need to make up a thin split steel ring shim to keep the crank seal away from the hot flange 'til it cools. If you can machine the seal housing to take a bigger id seal as large as the timing cover casting allows, by any means, so that the tapered flange part of the coupler is as large an od as is practible. Getting it all apart for servicing etc will be the problem. At worst it shouldn't shatter, just fret, if it doesn't hold. Put an alignment mark on the coupling/timing case referenced to a known engine timing position (tdc) etc so it can be monitored.

Something like the Hirth oil type coupling or similar, as used as on the Cov Climax flat 16, if still made, may work as your 'flexible coupling', should reduce the torque spikes that made it unsuitable for that particular application.

The coresponding front engine hub speaks for itself, but again high grade billet not welded. That welded stuff doesn't do it IMO.

I also agree with not bothering with the alignment snout/bush, just getting the engines into acceptable alignment.

Normal caveats about 'distance internet info apply.

"It's not always a case of learning more, but often of forgetting less"

RE: twin engine crank behaviour.

(OP)
thank you johnny,
after doing a little more research into taper locking hubs , and thier trq handling capabilites i have knocked up a hub and taper as a sacrificial item to do further research with ..



i used an old mini primary gear for the taper collet ,1.5 degrees angle .














working back from the taper lock hubs available ,and thier tech specs , this length and diameter of mating face would be good for around 1000 lbs/ft..... the taper used is not specified ,but i looked into this ,and decided to use similar to a morse taper ,which i think will be a fair bit stronger than the hubs available due to its being of a shallower angle , of course this will therefore require a very substantial puller to remove .

i'm still a little bit on the fence about whether to use a central locating spiggot or not .for and against comments greatfully recieved .
on the one hand , not having it would allow the engines to move a little bit more and not fight with each other .....on the other hand having a pin in the middle would keep the coupling from going into an orbital motion and them causing a big vibration , i know on my chassis dyno ,the coupling does not have a pin , but it is a lot bigger ,and also the two faces are bolted to pillow blocks and canonot really move , i am contemplating solid mounting the ends of the engine blocks nearest the coupling , leaving out the pin ,and very firm rubber mounting the furthur ends of the blocks ...that way the chassis flex will only affect the 10'' between coupling and hopefully be fairly minimal.

fun fun fun !

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

RE: twin engine crank behaviour.

Any word how SireCustom's coupling and crank snout attachment have been holding up, and how many miles and holeshots have accumulated?

RE: twin engine crank behaviour.

ivanheow-

If you can afford something semi-custom, take a look at some of the in-line engine couplings made for tractor pulling. These tractor pull components obviously are overkill for your application, but you can adapt the basic design for your engine coupling. And as I noted in a previous post, I would also highly recommend adding seals at each end of the spline joint so the teeth can be grease lubricated. This will greatly increase the spline life and reliability.





Good luck to you.
Terry

RE: twin engine crank behaviour.

(OP)
tmoose , he has 5000 miles of abuse on his link so far .i sm guessing he has simply added another keyway .
terry ,thank you for the pictures they are very interesting .

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

RE: twin engine crank behaviour.

Here is a Google search on gear couplings.
https://www.google.com/search?q=gear+coupling&...

I've used these in industrial settings many times. They are extremely compact for their torque capacity. You are allowed several degress of 3d movement so in your case chassis deflection is not a problem. I think you could modify one of these relatively easy for you app.

A spin off of these has been used in the Fuel drag racing for over almost 50 years. It is a standard for coupling the transmission or final drive in the case of only having a reverse unit to the rear end. They very rarely fail. However they are special made from high strength materials.

Even though alignment is not too critical, when we build drag cars we use a line up bar to align the crankshaft with the pinion in the rear end so it is 0-0 and end play is limited by special shaft collars.

A passing comment on crank loads mentioned above. We use a very critical front cover on these motors that has a large roller bearing that is carefully fitted to run true with the crank centerline. The blower on the top fuel cars can take up to 800 hp to drive at the speeds they turn. The crankshafts are very special forging, I think 4340 alloy heat treated. They use a splined crankshaft with a mating hub that rides on the ID of the front cover bearing. The crank snout is about twice the diameter of a small block chev.....so it is very large.

My own streetrod has a 3" 8mm belt driving a 6-71 blower. I only use 8 pounds of boost so the load on the crank is not high. The front bearing is like new even after 20k miles. I actually don't use boost very often....the car is very fast even at 1-2 psi boost. I also only use a single stock key and a press fit hub with no balancer. (do not need it with the blower.)

RE: twin engine crank behaviour.

Wow I thought I did daft things.

@Greg, was one not spinning the wrong way?

Brian,

RE: twin engine crank behaviour.

We never got close to a running engine - it was yet another failed supercar program. Yes one would have had to run backwards, or if you prefer, we'd have had a V12 with a split crank. Mercedes did that pre war with their I8 Grand Prix engines.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: twin engine crank behaviour.

Greg, saw a brm v16 up close and dirty 2 weeks ago - now that was crazy.
Making one engine of a matching set turn the other way hurts my head - mainly trying to convince yourself the cams just wont do no matter what. As with your case, went through all this before Christmas incl re doing oil drilling exit profiles on crank journals and the plug was pulled. Grrrrrr.

Brian,

ps, off topic, but a v8 maker that uses bike heads has a patent whereby he uses oem cams in both heads but turns one head. The left gets its chain drive from the bottom pulley as normal, but the right head is turned and picks up its drive from the flywheel end. He has an idler gear driven off crank which the chain drive is in turn taken off. This reverses the direction of rotation on the right head and its honky dory.
Using the oem head castings + cams/valve train keeps the cost down of finished engine to only' 35k and still allows users to buy cams from the aftermarket bike tuners that will fit right in.

RE: twin engine crank behaviour.

There's more to running an engine backwards, reliably, than the camshaft. It's not a show stopper but there is more than one gotcha, one I came up against was the direction of lapping on a bearing, if you lap the wrong way it wears out very quickly.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: twin engine crank behaviour.

Yeah, first time I saw directional polishing was in an old AE or Vandervell catalog maybe in the 70s. It was described as a possible cause of inserts worn into the copper/bronze.
It's everywhere now.
http://www.stealth316.com/misc/clevite-crank-grind...

I was thinking other directionally significant details might be cam chain tensioners, machined seal labyrinths or even spiraled lips, and the location of single feed oil holes in rod journals.

RE: twin engine crank behaviour.

The lapping is a good one - thanks. 'At least' thats one that you could just tell the engine re guys to ''run it the other way lads''
Finding space to put the timing belt tensioner because the tight run is now on the opposite side where the engine mount lies is something said guys dont want to hear about.
In hindsight, thank god it never saw the light of day - they wanted to keep the oil pump in its original buried location too

Brian,

RE: twin engine crank behaviour.

The group I worked with at one of the Northrupp Grumman marine divisions had never heard of, nor was concerned with directional polishing. So it surprised me when they ignored direction when they did spend what I considered an inordinate amount of time improving the surface profile of journals >> 2 foot diameter by polishing with abrasive paper using a fitted back up block. They called it "superfinishing" , but in my mind superfinishing is, and will always be what Chrysler "invented" back in the 1930s.
http://i.ebayimg.com/t/1939-Chrysler-Superfinish-D...

http://www.ebay.com/itm/1944-OLD-WWII-MAGAZINE-PRI...

http://books.google.com/books?id=NicDAAAAMBAJ&...

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