Is The Rotax 990 An Interference Engine?

[BLUEKNIGHT911]

I do not have to elaborate, as my title of this post says it all.

" interference engine " .... I'm beside myself with curiosity about the answer to this .....Mike

[larryd]

I think they are??? I think I remember years ago reading about someone with bent valves??? It may have been on that turbo charged 998 that was very active on the forum??? NOT 100% sure...larryd

[chipveres]

" interference engine " .... I'm beside myself with curiosity about the answer to this .....Mike

I think he means "If the timing chain breaks, do the pistons run into the valves?"

[BajaRon]

I think he means "If the timing chain breaks, do the pistons run into the valves?"

Actually, it's 'Can the pistons run into the valves'. It's important to note that just because an engine is of the interference design. It does not necessarily mean that stopping the valve train (i.e., timing chain breaks) will result in bent valves, broken pistons, or worse. It's Russian Roulette. It all depends on where the valves stop. The valves spend most of their lives in the closed position. So, it is very possible to break a cam or timing chain (same thing with different names) with no damage to the above mentioned parts.

However, breaking a belt will usually create no damage of it's own. Whereas breaking a timing chain can, and usually does, create a great deal of damage where it lives.

Cam chains, like the one used in the Rotax engines, rarely break. They usually last the life of the engine if proper maintenance is provided. But they can wear to an extent where the gears and chain, followers, etc., need to be replaced in very high mileage vehicles.

Belts, on the other hand, are going to break if you don't replace them at the appointed intervals. Highly recommended. At the very least leaving you stranded where it occurs.

[hypurone]

Actually, it's 'Can the pistons run into the valves'. It's important to note that just because an engine is of the interference design. It does not necessarily mean that stopping the valve train (i.e., timing chain breaks) will result in bent valves, broken pistons, or worse.

Sorry, but if the engine is an interference type, your chances of NOT having engine damage is higher than winning the lottery!! That is why they are designated as interference in the first place. The inertia of the bottom end is going to assure there is damage since there will always be valves that are open far enough to make contact...

In my 22yrs as an automotive tech I have never seen an interference engine NOT make contact, even when they seized!!

That said, with only 2 cylinders, a SEIZED engine may not make contact if everything lines up just right at the moment of seizure... But this is a moot point since you already seized the F'er and valve damage is the least of your worries!!