Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Incredibly violent banging under hard acceleratio?

Hi all,

(New here but loving this forum)

Driving my new M3W today on its first drive (with the exception of taking it home last week) and at one point I put the pedal hard down. I immediately felt a violent and very loud BANG-BANG-BANG. It sounded very destructive and I was sure the driveshaft had come loose or something. It does it in lower gears, the lower the gear the more violent it is. It sounds and feels like someone is hitting the underside of the car with the sledge hammer. Feels like it’s coming from the tunnel area. Anything up to about 75% throttle the car is fine though.

I can’t for the life of me work out what could cause this (I’ve built cars from scratch but the M3W certainly has some bits I’m not familiar with!). I’ve not found anything searching. Has anyone seen this issue before?

Thanks,

Greg

Probably the drive belt is needing tightening. They do need to run quite tight and once adjusted the rear wheel spindle needs done up pretty damn tight to keep the wheel where it should be and to keep the belt tight.
And welcome to the strange world of there daft little cars!

Ah you see! Never dealt with belts or bevel boxes! So are you saying the belt may be slipping and sending a shock to the bevel box making it buck into the chassis? That would be a wonderfully simple and easy to fix issue then. Comforting!

🤞🏻

Thanks

The NVH kit the bevel box is mounted on can make the noise you describe under very hard acceleration, as it is mounted on metalastic bushes which allows it to move, with this arrangement the belt needs to be tighter than you might expect. An alternative solution is to replace the NVH kit with Phil Bleazey's bevel box mount which bolts the bevel box solidly to the chassis.

Calum has a good suggestion and would be my first place to look. The NVH also does move, particularly once they get broken in or with age and as it moves it seems to change belt tightness under torque.

Thanks all!

I’ve been doing tons of research over the last few months and have become familiar with Phil’s modifications. I did also see that of all the technical improvements done to the M3W over the years the rubber NVH bevel mounts were the only thing that people considered a downgrade. I’ll have the belt tightened for now under warranty/service but I see Phil’s kit in my future!

I saw on the other thread there was talk of a rev limiter - you're not hitting that are you?

If it is a brand new M3W and you have just started driving it I hope you are following the break-in procedures, otherwise you could be doing more damage!!!!

It's quite a soft rev limiter if/when you hit it and is very unlikely to casue the violent banging.

99.9% the bevel box moving so, as above, first tighten the belt and then maybe consider Phil's upgraded mounting.

As a quick check - you should only be able to twist the lower run of the drive belt about 45 degrees or slightly over.

That's good, some of the 'bike' ones just cut the ignition when you hit it, leading to an almighty racket!