Is The Rotax 990 An Interference Engine?

[DaniBoy]

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

[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?"

[Little Blue]

Check out this on Google. Lots of good stuff.
As for the 990 Rotax engine being a 'interference engine' I don't know for sure but I think it probably could be.
Waiting for someone to come out and let us know. ....

[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.

[pegasus1300]

..... need to be replaced in very high mileage vehicles.....

Do we know yet what that mileage threshold might be yet with regards to the 998 V-Twin?

[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!!

[BajaRon]

Do we know yet what that mileage threshold might be yet with regards to the 998 V-Twin?

With a decently maintained Rotax engine. I don't think you'll ever need to change the timing chain. I don't know that anyone has ever worn out a 998

I have met a few Ryker owners who plan to run their CVT belt until it breaks as that is a bit of an expense every 10k. Not a good idea. When that belt breaks it can take a lot of expensive components with it. I don't mind cheating the maintenance manual on some things. But changing drive belts at appropriate intervals is the best way to go.

[Peter Aawen]

..... need to be replaced in very high mileage vehicles.....

Do we know yet what that mileage threshold might be yet with regards to the 998 V-Twin?

With a decently maintained Rotax engine. I don't think you'll ever need to change the timing chain. I don't know that anyone has ever worn out a 998 .....

There's more than 'just a couple' of early Spyders running around Oz with over 250,000 kms (approx 155,000 miles) on the odo without needed any timing gear replacement yet, and a couple that I know of that've done more than those miles that've had their dash units replaced cos they jagged in, & the new units can't be set to account for the previously accrued mileage, so they show less kms but have actually done somewhat more kms than that!! And IIRC, there's even a few similarly high mileage machines running around over in your part of the world without having had any major issues.

Basically, if you keep the maintenance up to spec; keep the oil level up (especially on the V-Twins ) change it regularly; and ride with juust a little mechanical sympathy, these Rotax engine things (especially the V-Twins ) just seem to keep on keeping on!

So all you V-Twin die-hards (like me! ), it looks very much like you can just Ryde More, Worry Less!

[bikerbillone]

So what is the recommended belt replacement mileage, say on a 2020 RTL?

[BajaRon]

So what is the recommended belt replacement mileage, say on a 2020 RTL?

As far as I know, there is no recommended belt replacement. Only periodic inspection. I'm talking about the drive belt here as the engine has a chain. No replacement recommendation on that either.

I did have a customer call me yesterday saying he snapped his drive belt. And it was only 2 years old! (A replacement for the rock damaged original belt). This is the first time I've heard of a snapped belt other than for a failed belt dampener taking it out. He didn't have any details so no telling what the cause was.

[bikerbillone]

Yes, talking belt, thanks Ron. I'm thinking, if ya don't abuse the belt, it's gonna last, but inspection is a good idea as is regular maintenance.

[BajaRon]

Yes, talking belt, thanks Ron. I'm thinking, if ya don't abuse the belt, it's gonna last, but inspection is a good idea as is regular maintenance.

The drive belt on the Spyder is way over-kill. It should last the life of the bike, in most cases. Subject to damage and dry-rot if not garaged. But other than this, a very reliable piece of equipment.