Prop angle

[RichardHyde]

Morning all,

What’s the correct angle for the prop ? Max has fabricated a gearbox mount which I can adjust to raise or lower the back of the gearbox.

I’m using the Sprint prop with a Nissan gearbox and Sprint centre bearing.

Hoping that some modifiers here know the answer !

Thanks, Richard

[cliftyhanger]

min 1, max 3 degrees max is the general advice. Ideally the flanges each end want to be parallel, but if a little out it doesn't seem to be an issue. At least that is my experience with my modified spitfire, and spitfires are very sensitive to propshaft balance etc. Dolomites seem to be far more forgiving.

[RichardHyde]

Does your Spitfire prop have a centre bearing ? Is it 2 piece ?

I’m hoping that it’s not that critical with the centre bearing. The centre bearing to prop angle is standard as I’m using the original parts…

[cliftyhanger]

single piece, and rather short.
Plenty of info out there, google is your friend!

[SprintV8]

What angle is your engine at?.

[RichardHyde]

Hmm…my garage floor isn’t level in any direction. That’s probably not much use of an answer, but I’ll find out what it should be…

[Carledo]

If your gearbox to prop joint is a sliding joint and a UJ, then Clive is right, no less than 1 degree, not more than 3. IMO you could stretch it to 5 at a pinch. I know the angle must not be zero as this leads to unpleasant driveline harmonics.

The Carledo has a rotoflex type coupling at this front joint and my Prop man says the angle for this type of joint should ideally be zero but in any case, no more than 1 degree. Since i'd already mounted the gearbox when he told me this, I just slapped the prop on and hoped for the best!

All I can say is I must be a lucky sod and accidentally got it just right by eyeball, cos 12 years 30k+ miles and countless hard starts later, that original, used, rotoflex from a 140k mile scrapyard Omega is still going strong!

HTH Steve

[RichardHyde]

I’ve got the standard Nissan sliding spline and UJ welded by PropTec (your prop man I think Steve) to the Sprint prop ahead of the centre bearing joint. They basically replaced the Sprint UJ with a sliding joint AND a UJ. There’s lots of moving parts so I HOPE the angle isn’t critical…
It’s a sliding joint / UJ, Sprint central bearing / sliding joint and the Sprint UJ.

[Carledo]

I’ve got the standard Nissan sliding spline and UJ welded by PropTec (your prop man I think Steve) to the Sprint prop ahead of the centre bearing joint. They basically replaced the Sprint UJ with a sliding joint AND a UJ. There’s lots of moving parts so I HOPE the angle isn’t critical…
It’s a sliding joint / UJ, Sprint central bearing / sliding joint and the Sprint UJ.

Yes it should be fine. So long as you have a slight angle beween the gearbox and the prop to avoid that dreaded harmonic, the rest should be no bother as it's just stock Sprint stuff. The central CV (rather than a UJ) will help too.

The only thing that bothers me slightly, is that you have 2 sliding joints, 1 in the gearbox and the other in the middle of the prop at the CV joint. You SHOULD get away with it if the length overall has been correctly judged. But just for safety's sake, when the prop is completely fitted and with the axle hanging at full drop, pull the front section of the prop backwards as hard as you can and make sure there's still enough prop inside the gearbox to maintain drive and keep the oil in!

Steve

[RichardHyde]

At that point, I’d also lose all drive !!

If I get any harmonics, I could space the gearbox mount up at bit. At least I’ve now got a starting point.

[Carledo]

At that point, I’d also lose all drive !!

If I get any harmonics, I could space the gearbox mount up at bit. At least I’ve now got a starting point.

Loss of drive is an inconvenience, having the prop turn into an impromptu pole vaulters pole at 60mph is another story and NOT one with a happy ending!

This happened to me once, many years ago when the front UJ failed on an old MKIII Zephyr. I was only going slow, nursing it home, as the vibration pre total failure was pretty fierce. Even so, at circa 15mph it had at least 1 and possibly both back wheels off the ground. A bit of a brown trouser moment! Mind, the Zephyr had a LONG single piece prop, it had a lot more leverage to work with!

Steve