Ever seen conrods like this?

[ivymike]

Hey folks, someone pointed this website out to me recently, and I've been scratching my head about it for some time now. I was wondering if anyone cared to comment on the conrod design pictured?

http://www.mid-usa.com/PHOUSE/engine.htm

Have you ever seen conrods like that before? Don't you think that the offset of the conrod big end relative to the cylinder axis could cause some problems? How do you suppose that they get away with it?

 

[franzh]

Only problem I see is that the centerline of the cylinder is not in line with the centerline of the con-rod. Looks like about 1/2" offset. This might cause some piston cocking in the bore and possibly some side loading on the rod big end.

If the rod cross section is stiff enough (looks like an "H" beam rod, but the beam is in the wrong plane for proper stiffness) it shouldnt cause any problems, but who knows, it might be ok. Even though, it looks strong enough.

Franz

 

[cycle]

Mike, This is an extremely strong setup. While it may not appear in the picture, one cylinder is slightly offset. This is a vast improvement over the older male/female arrangement. That setup had a female rod , with the big end "forked" if you will. the outer edges of each side of the fork rides on roller bearings. The male rode has a solid big end and is inserted into the female rod on a common crankpin.The male rod is also on rollers.The problem was/is the inherent weakness in the female rod. These were easily broken when pushed to hard. The male /female arrangement is still used by Harley Davidson.The side by side setup came about from the Harley Top Fuel bikes. This is the only setup that will withstand the 500 H.P. Nitro Fuelers of today.And now used on street H.D."s.. Craig

 

[ivymike]

I'm familiar with the fork-and-blade setup. It's also used in some aircraft engines, and in some bikes besides Harleys.

I thought that the mid-usa website specifically said that the cylinders were not offset?

 

[cycle]

Mike , My mistake. A typical Import Vtwin does in fact have offset cylinders when using side by side rods. I looked at Mid-USA"s sight . I did not realize the cylinders were kept in line!! Craig

 

[ivymike]

that's what brought my question up - they've got (sort of) S-shaped conrods, where the small ends are offset from the big ends, by about 1/2 big end width. Seems to me like a recipe for trouble, but apparently they're getting away with it. I was wondering what keeps the thing from gobbling the bearings or jamming the piston sideways in the bore?

 

[cycle]

Went to there site again. Read more about there odd piston design. It does state that there pistons have a special wrist pin bore. It also states that in place of a round (cam shaped) skirt,it uses a "triangular" skirt. This in turn causes, " the piston to follow the rod" !! Strange! Check it out again, And I believe the S shaped rods is an illusion , the shafts look that way to in the picture. Poor photography..... Craig

 

[evelrod]

It intrigued me enough that I asked my son in law, the Harley freak, about it . He says they run well and he has not heard of any big problems. One Harley, sans fairing, went 204 mph one day and 207 mph the next at El Miarage Dry Lake last year???? You'll have to look that one up, SCTA site I would guess.
I don't know anything about Harleys (I rode bikes from 1949 untill 1988 and still keep my license current, just NOT Harleys), but I do know about offset rods. My current project, the 1275 Cooper has the big end offset on all 4 rods! I have had bearing problems with these engines, years past, but not because of the offset.


Rod

 

[ivymike]

evelrod,

Is the middle of the big end offset relative to the cylinder bore? Would you mind giving me some more info about those conrods? I'm really getting curious about them. Diagrams, pics, manufacturer, etc., whatever you can provide would be appreciated.

thanks in advance

 

[evelrod]

Mike, the big end center line is along one side of the beam of the rod. Numbers one and two face each other and numbers three and four face each other, all on seperate crank pins with three main bearings, thrust taken by the center. It's a bore spacing problem. This basic engine started life as an 850cc and has progressed to as much as 1500cc. The 1500 verson uses an 86mm crank, quite a long arm for this little engine. The factory version of mine was 1275cc.( I've built as big as 1458cc before, 73mm X 86mm).
"Tuning the Mini" by David Vizard gives TOTAL info on these engines, used in a viriety of british sport cars, Austin-Heally Sprite/MG Midget, MG 1100, Austin America (US), all the versions of the Austin/Morris Mini, etc. Should still be available in print at speed merchants or

http://www.minimania.com

or

http://www.minispares.com

in the UK and brad@bishopsdev.demon.co.uk

If you just need general info. or demensions, let me know which and I will post them here.



Rod

 

[ivymike]

Rod,

if you happen to have a pic or drawing showing the profile view of one of these conrods, I'd love to see it (ivymike1031@yahoo.com).

What's the offset between the small end centerline and big end centerline (not the conrod "centers" length)? What are the SE and BE bearing widths (lengths)?

Thanks

 

[ivymike]

Rod,

Thanks for the pics. An interesting difference between the Mini design and the Mid-USA design is that in the Mini design, the cylinder axis intersects the big end bearing (eyeballing it, I'd say 1/3 of the way from one side of the bearing to the other), while the Mid-USA big end bearing is offset far enough that the cyl axis does not intersect it at all. It seems like both designs would induce some degree of conrod tilt (or require a moment reaction at the piston), but that the Mid-USA design would be far worse. Any comment?

Isaac

 

[evelrod]

Isaac, the big end of the late model rods is quite substantial for such a small production engine. These engines , in their larger displacement forms, are well undersquare with VERY long rods (reduces piston thrust to a minimum). The photo was of a 73mm by 86mm stroke 1458cc version (which I have reduced to 1380cc) but the graphics are from an 850cc or so early Austin-Healy. In the '60's we turned them 7500rpm and periodically lost MAIN bearings, but the rods did all right. The guys still racing these little wonders (one wonders why they are still running) are turning 9500rpm!!!!!!!! The rods, as spindley as they look, don't seem to give any problems.
I can't address the Harley stuff, all I have seen is the web site. But I can say that in racing, if it lives past the finish line it worked ok. One of the new members posted somewhere.---Speed costs, how fast can you afford to go? From the look of the web site, those boys are deep into 'Reganomics 101'---(You can fix anything if you throw enough money at it!!!)


Rod

 

[ivymike]

Yes, I noticed that the BE's looked a bit large. I was surprised to find that the offsets of the BE bearings were towards the flying webs. I had imagined that they would be away from the flying webs, to allow for larger webs. Seems like the crank is shorter than it wants to be.

 

[evelrod]

Isaac, have you seen a crank out of a Mini? Talk about short, the clutch is even on the engine side of the flywheel and the transfer gear is inboard of that. Only thing outward of the flywheel is the release ring for the pressure plate. Marvelous bit of engineering.


Rod

 

[ivymike]

Not yet. I've been thinking seriously about getting one of the new Minis when they finally become available. The only thing standing in my way is the Honda Insight, which ranks much higher in both fuel economy and "gadget factor." I'll probably end up getting the Insight, and wishing I had a Mini. Maybe a few years down the road I'll get a used Mini and beef it up a bit... mmmmmm... I'm starting to shake just thinking about it. Boy, my Honda Civic enthusiast pals would sure be disappointed in me if they knew the "dirty" thoughts I've been having about that Mini.

 

[GregLocock]

Save your dosh, mike. Get a real Mini, the new one is nothing to do with the old one. When you've bought, and driven, a 1960s era Mini, you will be left scratching your head - why can't (modern) FWDs handle?

Issigonis was the bee's knees, no-one since then has really had the guts to sort packaging out.

Cheers

Greg Locock

 

[WGJ]

Well pointed out Greg.
Yes the 'new Mini' only trades on the name of the original and is nothing more than BMW's entry into the SuperMini market. I had a good look at one and (other than the shape and the 'retro' instrumentation layout) couldn't see why it could be distinguished from any other European SuperMini. The model in question was about 14,500 pounds sterling - also nothing to do with the original Mini, which was spec'd and prices to make it affordable.
In my youth, many friends had Minis of varying types, from vans to a road-registered racer, and if you didn't mind the weak gearbox and the poor oil consumption that many developed, they're a real good laugh. I distinctly remember being driven in a Mini van into a corner that I drove my own car through at no more than 35mph at about 50 and wondering what the local hospital food was like, only to emerge unscathed and enthusiastic about Minis.
Like loads of stuff in life, the real thing is better than many imitations.

 

[GregLocock]

Oh, you want war stories.

OK, when I worked for a very excellent car company in foggy Norfolk I used to drive to work through the country lanes.

My Min, Kermit, was bog-standard, and an auto (so it wasn't very bog-standard). One day we were rattling along to work, foot to the floor, as I went down a downhill righthand corner, into a reasonably tight lefthand uphill turn. Unfortunately the people who lived on this corner had decided to move house, and parked a great big removal van at the entry to the lefthander. I braked and swung into the right hand lane.

To be confronted by an oncoming hoss and rider.

There was a gap, between horse and van, and I went for it, and we snuck through.

I admit, I was driving far faster than I should have been, and nearly hurt somebody else. But I am also convinced that the Min's linear steering saved at least one, and probably two people's lives that day. Cheers

Greg Locock

 

[WGJ]

Greg - sorry about the war story. However, as in a lot of the threads in Eng-Tips, the old adage of 'If you want to have a new idea, read an old book' certainly rings true. A lot of the suggestions that people make are based on personal experiences and old(er) techniques.
The original question about conrods is a good example, and your note on steering/handling is another. With the exception of Austin-Morris and Citroen (and certain low volume special designs), I don't think there have been many inovative package designs post WWII.
I also had a Wolseley '6' (2200cc straight six auto with typical Leyland FWD layout) and a 1700 Maxi for some years. Both of these cars drew hoots of derision from co-workers (Ford design people) until they had a ride in them and realised how much space there was inside and how flat, quiet and smooth the ride was in the Wolseley.
Its a pity Leyland went belly up due to Unions and Government. A modern engine and transmission in a hydrolastic platform could offer a really good package.