View Full Version : Dead engine

profqwerty - n/a
18-Jan-08, 04:52 PM
Well. I did the exhaust, sorry no pics now as it's dark. I eventually welded two small bits of angle onto the muffler and put a rubber mount between them and the fibreglass seems to be fine.

I was going round a flooded field and the thrust engine just came to a stop! I'm suspecting overheating as initially it wouldn't turn over, but did once cooled slightly.

However I've now lost compression in the magneto cylinder, as if the spark plug has been removed.

I took the heads off and everything seems to be intact, no nasty noises etc. There is a slight whiteish appearance on the MAG cylinder wall just above the exhaust port. It didn't seem to be scored or anything though.

Can anyone point to the problem?!?!?

This is a tad annoying as I had it going for only about 20 mins!!



Jamie Lewendon - n/a
18-Jan-08, 05:45 PM
Unfortunatly the whiteish stuff could well be the side of the piston.

Whip the barrel off and have a look at the side of the piston.


jon_curtis - n/a
18-Jan-08, 05:57 PM
did it run dry of fuel? have you checked the cooling belt fan tension? and the state of the pulley?

do you not have any gauges on the engine? EGT's are worht the investment as they can warn before damage occurs!

profqwerty - n/a
18-Jan-08, 06:06 PM
NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_cry.gif


Yes the white stuff is the side of the piston, and the rings all mushed together.

Hmpf. Can you just replace the one cylinder, or do both have to be done at the same time?

Does anyone have a spare cylinder + piston + rings they can part with?

Is it better value to change engine?

profqwerty - n/a
18-Jan-08, 06:18 PM
I have been advised that it could be a jetting problem, as the piston is on the exhaust port. I'm running a standard 447 SCSI, through standard Rotax exhaust. K&N filter.

Could the huge amounts of spray have cooled and shrunk the cylinder onto the piston at all?

What jet settings are other people using?

Jamie Lewendon - n/a
18-Jan-08, 06:51 PM

the barrel will repair, or at worst rebore. You can get it bored for about 25 squid. Piston is going to cost you though. However I would recommend you think carefully what you want to do with the craft, if you want to race it in F1X, you are going to want a 503 in there. Now may be the time to bite the bullet. If you are planning to just play in it, rebuild the 447.


p.s. can you resize the picture please.

profqwerty - n/a
18-Jan-08, 07:10 PM
I'm sliperily sliding down the 503 route at the moment.

Does anyone know if Kev T's 503 is still around? In an ideal world I'd be on the train to Devon on sunday to pick it up http://hovercraft.org.uk/images/icons/smiley_icons/icon_surprised.gif

tonybroad - n/a
18-Jan-08, 10:16 PM
if you can get hold of some dilute hydrochloric acid or a strong alkali it will dissolve a lot of the aluminium picked up on the bore - if the bore isn't scored underneath you shouldn't have to rebore

double check your jetting and two-stroke oil mix, adding too much 2 stroke oil leans things off as well

good luck and welcome to the world of hovercrafting, most of us have been where you are at some stage


jon_curtis - n/a
19-Jan-08, 09:19 AM
did your 447 have a rotax gearbox on it originally?

profqwerty - n/a
19-Jan-08, 11:39 AM
It used to have an A type with the high gear ratio. However it went to Bill Sherlock to use as spares.

I have been offered a 503 for 600. These are the specs from the seller; how does this deal sound?

"The engine was originally fitted to a "Thruster" microlite but after 8 hours the owner traded it back to Skydrive in exchange for the more powerful 532. The engine had been stripped of all the components so new items were fitted when sold to me. I have only flown 5 hours on it but it has been started and run regularly. I have the original bill of sale from Skydrive. The engine has twin carbs. amd a pull starter plus a spare. It is complete with exhaust and Mikoni pump and I also have an electric pump. I have the original throttle cable twinning adaptor but the engine is equipped with an improved version of my own design.

basic engine complete ~600"

I should be seeing it run tomorrow if the weather is ok.

nickyd - n/a
19-Jan-08, 01:38 PM

Sounds pretty good to me. Twin carb so it's the more powerful type.

Skydrive have serviced it so thats a good thing.

Retail at 2000 new so as long as it runs well and ain't too shabby go for it, stick it in and get racing F1X!!!

Might be worth checking compression whilst your there.


Jamie Lewendon - n/a
19-Jan-08, 10:00 PM
Sounds like a good deal to me too.


hoverchaps - n/a
20-Jan-08, 06:37 PM
fit a 4 stroke no more probs Mr Wilds has one 4 sale

Jamie Lewendon - n/a
20-Jan-08, 08:28 PM
Unfortunatly Duncs, fitting a 4 stroke doesn't always solve all the problems.

The craft has been set up for a 447, so will be easy to convert to 503 with relatively few mods, fitting a 4 stroke, would need a completely different ratio, so new pullies and belt, and possibly opposite fan direction, and unless he is really lucky, the crank height will be in completely in the wrong place, so a new fan frame will be needed.

He would also need to find space for another fuel tank to run the lift engine from.

All in all, fitting a 4 stroke in this case probably won't be the cheap option. However if he had started with a 4 stroke, that would be a different entirely


profqwerty - n/a
20-Jan-08, 08:42 PM
Jamie, that is exactly my reasoning.