Pre ignition pre detonation

[RogerSB]

My 1960 A10 GF combo got very hot this week after getting stuck in bumper to bumper traffic on Plymouth Hoe where there are dozens of speed bumps very close together along the length of the sea front (put there to stop boy racers using it as a race track). This necessitated being in first gear all the time with lots of stopping and starting and half the time pulling up hill. Also to make things worse there were cars parking at the meters on the side of the road. When I got clear of the traffic and speed bumps I noticed some lumpy knocking with a lack of acceleration when opening the throttle but only when my bike was labouring a little up hills. This disappeared when throttling down and on the normal fairly flat(ish) roads and normal use of the throttle, but I could get it to happen again immediately afterwards when labouring it up a hill (briefly) to test it.

Carrying on out of the city and on to Dartmoor, on the open road the bike went well again and at 55mph (pulling sidecar) I didn’t detect anything unusual and acceleration was fine.

I’m thinking it was probably pinking / pre-ignition / pre-detonation through being hot so today I thought I’d fit cooler plugs. I’ve been using Champion L82C, so changed to NGK BP7HS but I’ve not had a chance to test them yet. I’m also wondering about the timing and whether I need to reset it in case it’s now too advanced for today’s petrol.

Is there a consensus of opinion regarding the best ball park figure to use today for a Golden Flash’s timing advance (swing arm / iron head) measured through the spark plug hole? The books say 13/32” but with todays version of petrol I’m sure it won’t be that any more.

Also may be time for a de coke this winter  but don't relish taking the sidecar off and refitting again (took me months to get it set up right).

Rog.

[Colsbeeza]

Hi Rog,
Lumpy vs. pinking? 13/32" does seem too advanced, but suitable for high-compression pistons. That is about 37 Deg BTDC or 10.3mm BTDC, so may be a large contributor to the cause. I have set mine at 32 BTDC (that's 5/16"), runs nicely with L82C's but haven't flogged it hot yet. Mine is a bog-standard iron-head 1960 motor with 7.25:1 pistons. Orabanda's post on dynamometer testing suggests about 30-30.5 BTDC for optimum pulling power for an iron head, presumably under heavy load.
               https://www.a7a10.net/forum/index.php?topic=3747.msg25975#msg25975
That equates to about 9/32". That is miles less advance than yours.
It seems that modern fuels without lead need less advance. I understand that Lead slows down the combustion rate, so needed to be more advanced back then to deliver best power.
I am using Unleaded 95 here in Oz, still managing to avoid E10 ethanol. What fuel are you using?
I have attached Beezageeks spreadsheet with the rod length at 6.469", and my own which adds linear inches and millimetres.
Col

[trevinoz]

Roger, 13/32 was the figure for the late Rockets and was always problematic in regards to pinging.
Flashes were 11/32 and if you go way back to Orabanda's dyno tests you will find that is too much advance.
I like 5/16 which is what I have on my Flash with 7.25:1 pistons.

[Jules]

Ignition timing vs CR is always contentious but when you throw todays unleaded fuels into the equation for old engines, its all down to trial and error to get the best outcome...
Orabanda has done some really good ground work and come up with a good solution....only question then, is what fuel did Orabanda use to achieve that result (91/95/98 octane?) and did he check sensitivity to those fuels ie if the 5/16 setting was for 91 can you increase the advance for 95 or 98 octane and gain a bit more efficiency?

[BagONails]

Roger, Your pinking was most likely due to something glowing, a piece of carbon maybe as you say.

Bearing in mind I have not yet had the pleasure of setting the timing on one of these so this may be impracticable but otherwise maybe as a rough test with your new plugs fitted you could set up to your preferred timing figure given you've not had a history of pre-ignition. Fuel up with some fresh 95 or 98 octane and find a nice test gradient somewhere you won't annoy too many people. Get the rig fully warmed up then advance your timing and test and repeat, just to the point of pre-ignition occurring and then back it off a little. Make a note of what the new timing setting  is compared to your usual setting and make a decision on where to stay based on that if it is much more advanced than your starting point then maybe go somewhere in between, if it is close then this becomes your new figure and if retarded maybe it could stand coming up a little and test again. Make a note for future reference and you wouldn't be too far off the mark I would think.

[Black Sheep]

When my wife's Flash still had its sidecar for hauling the kids around, it too could get hot and bothered. I paid careful attention to fuelling and ignition timing but also fitted an alloy head for better cooling. Removing the sidecar was the ultimate fix.

[groily]

then advance your timing and test and repeat, just to the point of pre-ignition occurring and then back it off a little. Make a note

Encouragement to make the mag flange holes arcuate, to provide a few degrees of play-space? A massive time saving on bikes on which you can access all three fasteners without taking the timing cover off.
I also ran my iron 7.25 motor  at 5/16 btdc after reading Orabanda's test data from way back.

[Swarfcut]

 Ian's solution is the one to go for, advancing until it starts to pink/ping and backing it off a tad. In practice it's not that easy with an auto maggy.

 Bearing in mind the changes to fuel blends and the lack of lead ant-knock additives these days, the factory settings can only be considered a starting point and a suck it and see scenario as to what's best for you is the way to go.  Easiest is a dash of octane booster added to the highest octane fuel available locally.

 Mr G's adjustable magneto is another winner, even thinning down the mounting studs to give a bit more  movement rather than big cuts to the alloy flange.

 Those folks running a manual advance manual magneto don't have this problem.......


 Swarfy.

[Triton Thrasher]

I’ll chime in with “Don’t labour it up hills!”

Also try a richer needle height, if you haven’t already.

[RogerSB]

Thanks to all for the excellent advice. I’ll need time to take in everything that has been said, but I thought my next and the easiest thing to do is move the throttle needle up a groove (as I see TT has just suggested).

Col, thanks for those two useful attachments and also to Orabanda for constructing his chart in the first place.

Since 2017, to give my GF every chance, I’ve been using BP Ultimate 97 octane and I add Redex Lead Replacement, Fuel System Cleaner and Sta-Bil 360 Marine Ethanol Treatment. As mentioned here before I just add this to a 20 ltr can, fill the can up at petrol station and top up my bike from it at home. The 13/32” BTDC figure is what I’ve read is correct for a 1960 - 62 Golden Flash in my books (but that was in the day).  No idea what mine is at the mo.  When I bought this GF early in 2017 the p.o. had only done 17 miles and that was to take it for its MOT. He had only owned it for a year after buying it from a fellow BSAOC friend who was a HGV mechanic and who rebuilt the engine. So engine wise it was already in good shape when I bought it. I’ve improved it in other ways, such as new 4 spring clutch, new sprockets, chains, wheel bearings, wiring, DVR2, remote oil filter, etc., but for the engine I’ve only ever needed to carry out normal engine related maintenance to keep it running smoothly, i.e. tappets, changing and adjusting points. plugs, ht leads, mag pick ups, etc., that’s why the actual engine internals and the timing, at least for now, remains unknown to me.

I've not had this problem before and I think it was a combination of the circumstances at the time that highlighted it for a 62 year old veteran (GF that is). So at least now I know and will try to do something about it.

Rog.

[Triton Thrasher]

You’ll soon know if raising the needle is not the right thing to do.  It’ll be obviously too rich.

I have no faith in fuel additives and I see you’re using three different ones!

[RogerSB]

I have no faith in fuel additives and I see you’re using three different ones!

For landlubbers the Sta-bil 360 Marine is widely used in boats to help prevent the effects of moisture in Ethanol petrol. Only needs 16 ml for 20 ltrs, so a small 236 ml bottle does for 15 x 20 ltr cans of petrol.

Edit: Needle is on the book recommended No 3 for 389/45 carb. Ground electrodes on both my L82Cs were black but - but not sooty.

Just returned from a test ride with the NGK BP7HS fitted, gapped to 0.18". Bike started first kick and ran really well, so I feel a lot happier.  In fact I think it actually felt a bit smoother, maybe wishful thinking  - or did my episode burn off some carbon

Rog.

[Triton Thrasher]

For landlubbers the Sta-bil 360 Marine is widely used in boats to help prevent the effects of moisture in Ethanol petrol. Only needs 16 ml for 20 ltrs, so a small 236 ml bottle does for 15 x 20 ltr cans of petrol.

No explanation needed old boy.  It’s fine with me if you put forty different additives in your petrol and complain on forums that your bike runs funny.  Best of luck.

[BagONails]

 Mr G's adjustable magneto is another winner, even thinning down the mounting studs to give a bit more  movement rather than big cuts to the alloy flange.

 Those folks running a manual advance manual magneto don't have this problem.......


 Swarfy.

Swarfy, I'm not sure if this is a possible modification, have not had the chance to look in any detail yet but it would be nice to have both options wouldn't it.  Manual lever for baseline static setting and auto advance when running maybe?

[trevinoz]

The A10 engines pinged badly from new. I should say the high compression engines.
A good friend of mine bought a Super Rocket in 1962.
It always pinged and the cylinder head looked like it had been blasted by a shotgun.
My experiences from the late 60s was the same, pinging under load. And that wasn't excessive load. Admittedly I had high compression pistons and knowing almost nothing about anything, my solution was to use the highest octane fuel available at 150% of the pump price and not readily available. This problem solved itself when the barrel broke at the base. I had to do it twice to be convinced though.
Another friend had a Rocket Gold Star which went like a bullet, not Enfield, and he always set his advance at 5/16" as recommended by Eddie Dow.
I don't think that 13/32" advance was ever the setting for any Golden Flash.
Prove me wrong and I will humbly apologise.