Quote from DragonCommando :

A variable compression system will never make an engine more reliable, the more parts you add to something, the more there is to break.

Disagree. If the more complex engine had better engineering and better quality parts then it can be more reliable than an engine with lower quality parts and worse engineering.

Quote from DragonCommando :

The valve train in a 4-stroke is about as much as you'd want to add. Any more mechanical parts, like variable cam or intake, is just pointless parts that reduce reliability in the long run. If you take a non-Vtec honda engine and compare it to a Vtec engine of comparable size/power. The Vtec system is garanteed to be less reliable. Honda's engines are pretty good as far as reliability goes, but I would still take the simpler design over the Vtec version.

Not according to the Lotus engineers. I think they know more about what they're doing than you do.

Quote from DragonCommando :

A variable compression system will never make an engine more reliable, the more parts you add to something, the more there is to break.

The valve train in a 4-stroke is about as much as you'd want to add. Any more mechanical parts, like variable cam or intake, is just pointless parts that reduce reliability in the long run. If you take a non-Vtec honda engine and compare it to a Vtec engine of comparable size/power. The Vtec system is garanteed to be less reliable. Honda's engines are pretty good as far as reliability goes, but I would still take the simpler design over the Vtec version.

Every two stroke I've ever used short of chainsaws and small engine power tools has had problems, not so much reliability wise, but overheating is a big problem with 2-strokes. Aircooled 4-strokes have a few cycles to oil cool before the next ignition cycle. 2-strokes fire every up stroke, so they generate alot more heat.

I did have one 2-stroke blow the crank seals, and another fragged on a friend, but the fragging was because he didn't know how to shift.

My XL125s can run twice as long, and twice as hard as my friend's yamaha 2-stroke.(can't remember model) Both bikes are from around the same era, aside from his mono-shock, everything looks very similar even.

The yamaha just seems to overheat on the trails, it starts backfiring and missing and we know its time to let it cool down. My 125 has only done that once, after running it slow in low gears to get through a swamp.

It's just a concept engine, and yes it's a bit more complicated than the stone age 2 stroke engines you find it little dirtbikes, but I think the similarities would pretty much stop at them both being 2 stroke.

I know, everyone knows, that 2 strokes notoriously are more prone to seizing, and that adding parts means there is more to go wrong, but you know I reckon there's a chance Lotus engineers might know that too.

So many times I hear that "they are engineers, they know what they are doing" line.

These kinds of "advances" in engine technology only make it harder for mechanics to repair the engine when it fails, and add useless complication. Most of the time it takes these things several generations before they become even decently reliable, if they do at all.

Like I said, if you take a honda engine without Vtec, and a honda engine with Vtec, the non vtec engine will always be more reliable, less parts to break means lower chances of failure.

Thats why someone has a model T ford that still runs and has never had a rebuild. It's so simple it just doesn't have a big chance of failure. Where newer engines have become so complicated that they have way more parts than they need.

My 1981 XL125s still runs, it's just never failed, but my friend's 2008 baja 125 is falling apart after 1 year.

It's just my opinion as a mechanic that these things just add more problems than it's worth.

Quote from DragonCommando :

So many times I hear that "they are engineers, they know what they are doing" line.

These kinds of "advances" in engine technology only make it harder for mechanics to repair the engine when it fails, and add useless complication. Most of the time it takes these things several generations before they become even decently reliable, if they do at all.

Like I said, if you take a honda engine without Vtec, and a honda engine with Vtec, the non vtec engine will always be more reliable, less parts to break means lower chances of failure.

Thats why someone has a model T ford that still runs and has never had a rebuild. It's so simple it just doesn't have a big chance of failure. Where newer engines have become so complicated that they have way more parts than they need.

My 1981 XL125s still runs, it's just never failed, but my friend's 2008 baja 125 is falling apart after 1 year.

It's just my opinion as a mechanic that these things just add more problems than it's worth.

If we all had that attitude, we'd still be living in caves.

Quote from DragonCommando :

It's just my opinion as a mechanic that these things just add more problems than it's worth.

Ah right, seen a lot of variable compression ratio alcohol burning direct fuel injected 2 stroke concept engines have you? Maybe your friend's bike has one?

I'm glad you put that's it your opinion, so I won't argue the point any further. It's not like every other 2 stroke engine, and if you as a mechanic want to conclude that "it'll never work" from one crappy little animation then that's your choice.

Quote from 5haz :

If we all had that attitude, we'd still be living in caves.

+1

Also, in my experience with mechanics most of them would be happy to have less reliable engines because then they could shaft you even more on the bill. Saying engineers shouldn't try to introduce technology to improve fuel economy, performance, emissions etc is an indefensible position.

Wow you people baffle me again and again how you take things way out of context. New technologies are always going to be developed, but its how they go about it that is important. Simpler is the most important fundamental of design, the less moving parts, the more reliable it will be.

That design has a weakness right at the top of the engine, if something up there fails it will blow the top off. Engineers don't think the same way mechanics do, they design things to function on a computer, but often times the design isn't practical, its just too complicated.


I have already, within a day, figured out how to make that engine more reliable and less complex. I could even draw it up and make an animated representation exactly the same as they have. I'm lucky enough to see it from both perspectives, as an engineer, and a mechanic.

Instead of running so many extra parts on top of the engine, just make the very bottom of the cylinder barrels telescopic, so the head can stay one single bolted together unit, but the whole thing can move up and down to change the compression. Then run a variable geometry expansion chamber and have flexible hoses run fuel and cooling.

Since it is a two stroke, the crank case transferes air and fuel to the cylinder, so you only need very simple seals on the telescopic part, and they would be easy to change as well. Additionaly, the telescopic system could run off simple rods with hydraulics. The whole thing would be easy to take apart, easy to repair, and be much more reliable.


I'm never against new ideas or technologies, I just hate it when I see engineers get alot of money to do horrible design jobs that could be much simpler and more reliable.

Quote from DragonCommando :

Instead of running so many extra parts on top of the engine, just make the very bottom of the cylinder barrels telescopic, so the head can stay one single bolted together unit, but the whole thing can move up and down to change the compression. Then run a variable geometry expansion chamber and have flexible hoses run fuel and cooling.

Since it is a two stroke, the crank case transferes air and fuel to the cylinder, so you only need very simple seals on the telescopic part, and they would be easy to change as well. Additionaly, the telescopic system could run off simple rods with hydraulics. The whole thing would be easy to take apart, easy to repair, and be much more reliable.

So you'd basically be lifting (or extending) the cylinder, relative to the crankshaft, to reduce the compression ratio?

Nice idea, but wouldn't the intake port and exhaust port move up and down also? You'd then need some kind of variable piston stroke for it to run properly. Unless you had ports that slide up and down the cylinder walls and remain the same distance from the crankshaft so that the piston always clears them by the correct distance, no matter what the compression ratio.

The variable geometry expansion chamber could be used to compensate for that a bit, and even then the change in port position wouldn't be very large.

Lotus seem to have a system for changing port size, and it appears to do it in a way that could be adapted and simplified to change port possition instead if you realy needed it to. But I don't think it would be critical as long as the cylinders don't lift alot.