Some of the worse designed engines? 2

[enginesrus]

Just a fun thread. Lets talk about some of the worse designed engines not going back past the 40's, and all types, sizes and applications.
Why do they get the vote as one of the worse designed. I decided to do this not so much as to talk bad about a particular manufacture, but to hopefully help them and others improve the design.
In many cases such manufactures have other engines that are just fine or have improved what was a not so good design. Maybe we can do this without mentioning any particular brand if that is frowned on in here.
If this is not so good an idea, then the moderators can just delete this.

 

[Lou Scannon]

The Deltec being a two-stroke, I don't see an inherent reason that any of the cranks has to rotate in a particular direction. The rotational direction of each crank would be an outcome of the detail design. There could be some nuance to the piston phasing so if that drives the need for one crank to rotate opposite the other two I would like to learn the reasoning behind it.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[BrianPetersen]

It has to be that way. In that animation, pay attention to the firing pattern. The combustion events are 60 degrees apart and then there's half a revolution with nothing. To make that work, the phasing of the two pistons on one crank has to be the other way around.

 

[RodRico]

Probably more than you ever wanted to know about the Napier Deltic:

https://oldmachinepress.com/2019/09/05/napier-deltic-opposed-piston-diesel-engine/

 

[RodRico]

It looks like Fairbanks-Morse outdid the Napier Deltic with the Diamond opposed-piston two-stroke with four cranks.
It was commissioned by the US Navy in 1940 and the prototype was completed in 1942.
Detailed description and history:

https://oldmachinepress.com/2019/08/20/fairbanks-morse-diamond-opposed-piston-marine-engine/

 

[RodRico]

I think that engines of this era suffered from poor detail design, compared with modern finite element methods etc.

I believe all these opposed piston two-strokes are traceable back to the Junkers Jumo 205 (see

http://www.enginehistory.org/Piston/Diesels/CH4.pdf

). There have been many attempts to commercialize the opposed-piston two-stroke diesel (including my own). The leader of the modern effort is Achates Power who is using contemporary simulation tools to address the design's shortcomings. You can see some of their simulation work at

https://achatespower.com/cool-idea-for-engine-design/

. If you look at their news page, you'll see a lot of activity including funding from several government agencies as well as collaborative efforts with both Cummins and Ricardo:

https://achatespower.com/news-blog/

To the best of my knowledge, the primary drawback of the opposed-piston two-stroke is its tendency to lose oil from the cylinder walls out the exhaust ports. Large marine versions of the opposed-piston two-stroke from Wärtsilä and Mann use high precision metering of oil onto the cylinder walls to mitigate the problem. Per an SAE article (

https://www.sae.org/publications/technical-papers/content/2019-01-0068/)

Achates "directly addresses these concerns by utilizing intake and exhaust manifolds, a closed crankcase system, and oil control rings which operate outboard of the ports. Previous work has shown the importance of careful consideration of cylinder liner, piston, and ring design in minimizing oil consumption of the OP2S architecture. This work evaluates further refinements in cylinder form, hone texture and oil retention, port sealing ring design, and oil control ring design." My design, a rotating cylinder radial opposed-piston two-stroke, mitigates the problem in two ways: 1) it employs a simple low precision oil metering system and 2) it exploits centrifugal force combined with port features to recover oil exiting the ports.

 

[NickJ67]

Been a number of deeply suspect engineering decisions in the engine departments of VAG and BMW in the last 15 years or so.

Insufficient piston ring tension margins giving huge oil consumptions at low mileages. (Also Toyota though)

Ridiculously complex timing-chain arrangements with inadequate tensioning arrangements - sometimes located at the wrong end of the engine, just to make fixing them even worse.

Timing chains in the middle of the engine necessitating the drive sprocket being formed as part of the crank.... what could possibly go wrong?

Oil pump drives tacked on the end of largely unnecessary balancer shafts.

Over-complexity as a general theme.

Recently worked on a friends 2005 Audi A4 V6 2.5 TDI (actually not one of their worst), where the cam lobes had come loose from the hydro-formed shaft and caused general mayhem in the valve-train. A quick count up of the components in just one head got me thinking.... Nearly as many as the whole of my previous gen I5 2.5TDI - which is definitely one of their better efforts.

As for the Olds diesel effort, a different friend though it would be "interesting" to buy a Range Rover which had been converted with one of these engines. I have no idea why he thought that was a good idea, or indeed why the original owner thought it a good idea to convert in the first place. WE learnt pretty quick that it was a big mistake. The only thing that engine if good for is to stop your boat drifting away - and it could hold a pretty big boat.... damn it was heavy!

Nick

 

[Lou Scannon]

It has to be that way. In that animation, pay attention to the firing pattern. The combustion events are 60 degrees apart and then there's half a revolution with nothing. To make that work, the phasing of the two pistons on one crank has to be the other way around.

Thanks for that. Of course, a triangular arrangement doesn't fit elegantly to a two-stroke cycle; they might have considered a "quadric" instead for a more elegant layout, but then again why bother, what's wrong with a two-crank concept if you're determined to have an opposed layout?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[turbomotor]

I am surprised that no one mentioned the OPOC engine. Or perhaps it doesn't count, as I don't think it ever saw production.

 

[TugboatEng]

One of the advantages of uniflow 2-stokes whether poppet valves or uniflow is asymmetric port timing. In opposed piston engines the exhaust crank lags behind the primary crank.

 

[RobWard]

I believe Thiokol came up with an 8 piston cross shaped engine with four pairs of parallel pistons (sort of # shaped) but I'm unable to find much about it.
I'd love to know a bit more about it.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[RodRico]

I believe Thiokol came up with an 8 piston cross shaped engine

The only reference I could find relating to a piston engine from Thiokol is the "Dyna-Star." You'd have to pay $33 to learn more.

 

[kjoiner]

Hello,

Regarding the Deltic engine, I remember seeing an article about Clen Tomlinson who was working on a scale model. He machined all of the parts. His work was stellar. Here are some links:

https://www.craftsmanshipmuseum.com/Tomlinson.htm

http://www.enginehistory.org/Convention/2005/napier_model_engines.shtml

Kyle

 

[gruntguru]

Dedication!
The first link states the model as 1/8 scale, the second link 1/4 scale (unlikely).

je suis charlie

 

[PJGD]

So far, I am failing to see why the name Napier would appear in any thread supposedly about engines of the worst design. Impressive, certainly, but never worst.

As for the Dynastar, these photos are not from the web, but there is plenty of information out there about it, but again the thread seems to have diverged from worst to "interesting" engines.

As an engine that might rank among the worst, consider the 8.2L Leyland 500 fixed head bus engine from 1968. It was designed by the best brains at Leyland at the time and had many good features including timing gears at the rear "nodal" point, and the fixed head was intended to obviate head gasket failures. Most of the time the engine worked quite well, but because the parent bore cylinders were anchored to the cylinder block at the crankcase interface, and necessarily at the top end of the engine also, the problem was that on cold mornings if you drove off immediately after starting up the cylinder would heat up and expand axially faster than the external walls of the block and shear the inlet and exhaust ports hence flooding the cylinders with coolant. So much for no head gasket failure modes.

PJGD

 

[TugboatEng]

Any cross-flow 2-stroke is the worst engine design. They ran, sure. But that's about it.

 

[michaelwoodcoc]

GregLocock (Automotive)90 degree V6s. Horrible balance issues.

First gen NSX used honda's race winning V8 block design (90*) with two cylinders lopped off then they offset the crank bearing/pins/ whatever you'd like to call them 30*. All if I remember correctly. Not sure what else.

The worst design I ever saw was a two stroke scooter with the oil pump driven off the transmission / rear wheel. It was a chinese mantis scooter. I got it for free, barely running, worked on it periodically and it only got worse until I figured that oil pump situation out. It was such that it only pumped oil when you were actually moving. Made absolutely no sense with a CVT as there was no direct relation between oil flow and engine RPM.

Engineering student. Electrical or mechanical, I can't decide!
Minoring in psychology

 

[RodRico]

it only pumped oil when you were actually moving

WTH were the engineers thinking? Perhaps I presume too much thinking there were engineers involved.

 

[3DDave]

It's a scooter not a stayer.

 

[RodRico]

It's a scooter not a stayer

LOL! No stoplights allowed, only roundabouts! What's the benefit of only pumping oil when moving?

 

[3DDave]

No wasting fuel idling at lights.