NH 350 engine rattle

[MarkPhillips]

Hi my names Mark
Bought a 1959 Ariel Red Hunter last Autumn complete and in fairly good cosmetic order, been standing for about 3 years.
Basically unrideable due to knackered gearbox carb and brakes.
Spent a lovely winter sorting out a hundred n one bodges and getting things to work as they should including rewire, gearbox rebuild new carb and Thorspark ignition plus lots more.
Pleased to say she starts Ist prod ticks over lovely is smooth n nice to ride if not a little gutless, I would guess 12hp 55mph top end but I’m cool with that love the character.
I am however concerned with top end engine rattle, rises n falls with revs, hot or cold makes no difference is very noticeable.
Can’t find anything obvious.
Valve clearance 6 thou inlet 8 thou exhaust, spark plug colour good, no smoke and compression feels strong to me need decompresser to kick her over.
Engine was supposed to have been rebuilt 1000 miles 6 years ago have some receipts.
Loathe to tear it down when it runs so nicely.
Been told late ally head NH Red Hunters are noisy, am I worrying about nothing.
Any advice would be welcome
Cheers Mark.

[will_curry]

How are you setting the tappet clearances?

According to the User Guide the inlet is set with the exhaust valve just starting
to open and the exhaust is set with the inlet just closed bot being set with the
engine turned in the 'Driving' direction.

[pete.collings]

When setting the exhaust valve clearance, disconnect the valve lifter (by removing the cable from the lifter arm) and rotate the arm to be well clear of any engagement with the rocker arm. I once helped an experienced single owner remove an annoying clatter by doin this!

[nevhunter]

It should be Over 17 Hp Maybe 23 at best, but the Bike is not Light. The alloy head is NOISY. Every rattle comes out through the fins, amplified. If the Motor has done Say 40 K miles it would deserve a strip. Often sitting motors get corrosion in Ball and roller bearings. Big ends fail by pitting and Peeling of the Hardened surfaces Timing gears develop backlash that is Noisy Remove the Oil tank and clean it out THOROUGHLY. Also the Plate and gauze filter at the bottom of the Motor and the Centrifugal hollow bolt in the flywheel and scratch out all hard sludge. Don't round off the Hex head. Use a tight fitting socket and Tap the Head first a few times with a brass bar Propelled by an engineers Hammer A couple of sharp cracks will do wonders. IF it all seems OK put the Minimum amount of Oil in and go for a local test ride, Use a decent oil with a bit of guts in it. Keep your ears open for any Noise Increases of the Mechanical kind. Nev

[MarkPhillips]

Thank you all for your prompt replies.
I cleaned the oil tank out spotlessly when I took the entire back end of the bike off, to paint the frame mud guard chain case and rewire the electrics.
Also cleaned the sump and removed the centrifugal filter in the crank which was spotless.
When I rebuilt the bike I used Golden film W40 in the engine and W30 in the gearbox and primary chain case.
I dropped the sump last week after 400 miles and ran a magnet through the small amount of oil that came out, nothing to report at least not wet sumping.
I also checked the valve clearances back in the winter, but I will confess probably not to the procedure you laid out
Used to just setting valves at TDC.
Any way set them the recommended way with the decompressor disconnected.
Made a difference straight away, engine still very mechanically noisy but not as rattly as before if that makes sense.
It also rounded up3or4 of those missing ponies.
Went over to Buckfastleigh to the south Devon railway yesterday, lovely spot for a couple of hours ride.
Engine more responsive and a lot better up hills of which there are many down here, a really pleasurable ride.
Once again thank you for your help Mark.

[Julian Murphy]

Just my opinion of course, but I think the oils you are using are on the 'thin' side.

I'm using SAE 50 in the engine, gearbox and primary chaincase.

[nevhunter]

After about 1976 Engine oils were not permitted to use the additives that Gearboxes use as they Kill the Catalytic Converters
There's also not a lot of Aircooled Motors out there on the road these days so most of the Oils suit the other types where Fuel economy is often a Major consideration. Keep the thin oils out of these old bikes and they will run a lot quieter. As to the gearbox and cushion drive, something better than engine oil be used, I would advise. Like an AGRI Multi use Hydraulic/gear oil 75-90 (equal to SAE 60) Non foaming and anti rust and suitable for the Forks also. Been using it for years. Nev

[MarkPhillips]

Once again for the replies it’s great to get advice on this forum. Geoff Brown AOMCC was a great help with parts and advice when doing my gearbox great bloke now’s his stuff.
When I rebuilt the box I used hypoid 80/90 gearbox transmission oil used it all my life never had an issue.
But then I read on this very forum not to use it as it could possibly corrode brass/bronze bushs.
So I dropped that and went to engine oil, not as good.
I’ve now got Castrol classic 90W gearbox oil in there, a lot better.
I’ve also got some 50W classic engine oil from Smith n Allen very good price and delivered promptly on eBay.
I’ll give this a go at the next oil change in 350 miles see if she quiets down a bit, won’t be long can’t keep of this bike love it.
Once again thanks
Cheers Mark.