SteveBorland
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- Joined
- Nov 15, 2010
- Messages
- 776
Sorry for the very long post (and rather late, considering that Spa was the first weekend in July), but some may find it interesting, and of course I’m open to other suggestions as to what went wrong and how to avoid it..
Spa this year was held in near perfect weather, if a touch on the warm side, but all did not go as planned and the weekend ended up a bit more expensive than originally planned.
Due to work interfering in my private life, I had done very little to the bike prior to leaving, the main items being a Maney belt drive (mostly s a good way of raising the gearing) and the new Falcon shocks. I only managed to get the bike up out of the workshop a few days before we left, and the total running time was the 20 min or so required to ride up to a friend where we could put it into a van for the trip south.
I had some strange experiences when doing the first starts though. Immediately after dragging the bike up onto the street, it fired up on the first or second kick. I did a quick check for oil return then shut off to finish doing stuff such as bolting the tank and seat on, that sort of thing. Tried to start again to check that the new belt was running true on the pulley, no joy whatsoever. Just the occasional PUFT!! and a slight tendency to kick back.
Hmm, what to do? I ended up pulling the rotor on the Paton ignition and retiming it. This eventually resulted in the beast roaring to life again, but I still do not understand what could have happened between the first easy start and the next. Gremlins at work I suspect...
However, it was getting dark, no time for pointless speculation (sorry for the bad pun!!) so I rode home, with the bike feeling good, as much as you can test at 10pm in a crowded city that is.
Next day, off to drop the bike off at a friend's garage from where it would be picked up in the van, Again, no problems at all.
All was looking good, and the first track session confirmed my idea that new rear shocks (I chose Falcons) were a great step towards a stable bike in the fast sweeping corners that abound at Spa. Since the bike had not had much use on it since 2018, I took it fairly easy round the track, but all seemed well indeed. I had a look at the plugs after the first session, and they seemed fine. The rest of Friday was spent in playing with the suspension and Iso settings, but I ended up very much where I started from. Th rather worrying tendency to do a long slow roll or wallow in the fast corners from last year was gone, I went able to push the bike more.
First session on Saturday, again, not going flat out on the main straight (it's very long and uphill, a real engine killer if you get too enthusiastic, at least on an old classic. Towards the end of the straight, I felt the engine stumble slightly, then pick up again. I eased off the throttle, then mid way through the right -left set of bends at the end of the straight, it just died, rather as if it was an electrical fault.
Back in the paddock, I found that the left carb manifold had lost one bolt, and the other had backed off enough to let the carb swing down, creating a massive air leak.
I pulled the plugs, and the left plug had a fine coating of aluminium, the right side looked normal (to me at least).
What to do? I did a rough compression check with my thumb, yes there’s compression. Replaced the missing bolt, new plugs and a quick blast down the access road showed the bike was still willing, so I did the next session as well. Took it easy on the straights, but gave it some stick in the bendy bits. Bike was pulling strongly, handling was good, looks promising.
Back in the paddock though, the left plug still has some traces of alloy on it, and a check with a borrowed compression tester showed a large loss of compression on the left side - something like 80 psi vs 160 on the right side, so I parked the ike an become a spectator.
Los of interesting bikes to be seen and oogled at, probably the most impressive was our neighbour, last year he had a very quick Seeley Norton, this year he brought a very rare factory MV750 racer with chain drive, one of only 3 made. A problem with the carbs however meant that it only did part of one session, more’s the pity. at Spa was the very first time he had stated the bike, having just finished a complete strip down to check the internals. It had been sitting in museum for 25 years before he bought it, no idea how much it's worth, but it's lots. He mentioned that Dave Kay, who does lots of reproduction stuff for MV's in the UK offered him a new set of 4 carbs at over £6000 - the original unobtanioum race MV carbs are worth something like twice that. Serious money, so more praise to him for wanting to use the bike rather than just show it.
Back home, various other stuff meant that I did not have time to look at the Norton until last week. Pulling the head revealed 2 rather damaged pistons, bugger!
I’ve had a good correspondence with my piston pusher, Jim Schmidt, who has been every helpful. The conclusion is that while the timing may have been a bit advanced (Jim recommend 28 degrees) and the plugs one grade too hot (BP7 instead of BP8), the sudden leaning off of the mixture was sufficient to cause failure and loss of a lump of the left hand piston around the inlet valve, while the balance tube seems to have leaned out the right side for failure to start (distortion and cracking in the same place, but no loss of bits of the piston).
You may remember that I was asking how people secured the carb manifold bolts, this is why.
An interesting (if if rather expensive) offering to the Gods of Speed, but I’ve learnt the following:
The most failure-prone of the piston (at least on Norton high compression ones) is not around the exhaust valve as I had thought, but around the inlet because there is less material here. Jim has said that my next set of pistons will have the rings 0.5mm lower to help this)
It’s a good idea to recheck the ignition timing before going out on the track for the first time after doing some work on the motor
It’s a really good idea to do frequent checks for air leaks
You cannot really use the spark plug colour as an indication of the actual conditions in the engine once you have motored back to the paddock, since that period of idling changes the plug colour. Actually, unless you really know what you are doing. Belgian 100 octane burns with a different colour to the 98 octane I use up here, so everybody peering intently at plug colours are really only confusing themselves. Probably best ro find a local 2 stroke racer and ask them (apart from the fact that 2 smokes colour their plugs with the oil they burn, so that’s probably not a good idea either
And lastly, its a Really Good Idea to do a bit more testing at home before flogging the bike down (up?) the main straight….
Sorry for the very long post, but some may find it interesting, and of course I’m open to other suggestions as t what went wrong.
Spa this year was held in near perfect weather, if a touch on the warm side, but all did not go as planned and the weekend ended up a bit more expensive than originally planned.
Due to work interfering in my private life, I had done very little to the bike prior to leaving, the main items being a Maney belt drive (mostly s a good way of raising the gearing) and the new Falcon shocks. I only managed to get the bike up out of the workshop a few days before we left, and the total running time was the 20 min or so required to ride up to a friend where we could put it into a van for the trip south.
I had some strange experiences when doing the first starts though. Immediately after dragging the bike up onto the street, it fired up on the first or second kick. I did a quick check for oil return then shut off to finish doing stuff such as bolting the tank and seat on, that sort of thing. Tried to start again to check that the new belt was running true on the pulley, no joy whatsoever. Just the occasional PUFT!! and a slight tendency to kick back.
Hmm, what to do? I ended up pulling the rotor on the Paton ignition and retiming it. This eventually resulted in the beast roaring to life again, but I still do not understand what could have happened between the first easy start and the next. Gremlins at work I suspect...
However, it was getting dark, no time for pointless speculation (sorry for the bad pun!!) so I rode home, with the bike feeling good, as much as you can test at 10pm in a crowded city that is.
Next day, off to drop the bike off at a friend's garage from where it would be picked up in the van, Again, no problems at all.
All was looking good, and the first track session confirmed my idea that new rear shocks (I chose Falcons) were a great step towards a stable bike in the fast sweeping corners that abound at Spa. Since the bike had not had much use on it since 2018, I took it fairly easy round the track, but all seemed well indeed. I had a look at the plugs after the first session, and they seemed fine. The rest of Friday was spent in playing with the suspension and Iso settings, but I ended up very much where I started from. Th rather worrying tendency to do a long slow roll or wallow in the fast corners from last year was gone, I went able to push the bike more.
First session on Saturday, again, not going flat out on the main straight (it's very long and uphill, a real engine killer if you get too enthusiastic, at least on an old classic. Towards the end of the straight, I felt the engine stumble slightly, then pick up again. I eased off the throttle, then mid way through the right -left set of bends at the end of the straight, it just died, rather as if it was an electrical fault.
Back in the paddock, I found that the left carb manifold had lost one bolt, and the other had backed off enough to let the carb swing down, creating a massive air leak.
I pulled the plugs, and the left plug had a fine coating of aluminium, the right side looked normal (to me at least).
What to do? I did a rough compression check with my thumb, yes there’s compression. Replaced the missing bolt, new plugs and a quick blast down the access road showed the bike was still willing, so I did the next session as well. Took it easy on the straights, but gave it some stick in the bendy bits. Bike was pulling strongly, handling was good, looks promising.
Back in the paddock though, the left plug still has some traces of alloy on it, and a check with a borrowed compression tester showed a large loss of compression on the left side - something like 80 psi vs 160 on the right side, so I parked the ike an become a spectator.
Los of interesting bikes to be seen and oogled at, probably the most impressive was our neighbour, last year he had a very quick Seeley Norton, this year he brought a very rare factory MV750 racer with chain drive, one of only 3 made. A problem with the carbs however meant that it only did part of one session, more’s the pity. at Spa was the very first time he had stated the bike, having just finished a complete strip down to check the internals. It had been sitting in museum for 25 years before he bought it, no idea how much it's worth, but it's lots. He mentioned that Dave Kay, who does lots of reproduction stuff for MV's in the UK offered him a new set of 4 carbs at over £6000 - the original unobtanioum race MV carbs are worth something like twice that. Serious money, so more praise to him for wanting to use the bike rather than just show it.
Back home, various other stuff meant that I did not have time to look at the Norton until last week. Pulling the head revealed 2 rather damaged pistons, bugger!
I’ve had a good correspondence with my piston pusher, Jim Schmidt, who has been every helpful. The conclusion is that while the timing may have been a bit advanced (Jim recommend 28 degrees) and the plugs one grade too hot (BP7 instead of BP8), the sudden leaning off of the mixture was sufficient to cause failure and loss of a lump of the left hand piston around the inlet valve, while the balance tube seems to have leaned out the right side for failure to start (distortion and cracking in the same place, but no loss of bits of the piston).
You may remember that I was asking how people secured the carb manifold bolts, this is why.
An interesting (if if rather expensive) offering to the Gods of Speed, but I’ve learnt the following:
The most failure-prone of the piston (at least on Norton high compression ones) is not around the exhaust valve as I had thought, but around the inlet because there is less material here. Jim has said that my next set of pistons will have the rings 0.5mm lower to help this)
It’s a good idea to recheck the ignition timing before going out on the track for the first time after doing some work on the motor
It’s a really good idea to do frequent checks for air leaks
You cannot really use the spark plug colour as an indication of the actual conditions in the engine once you have motored back to the paddock, since that period of idling changes the plug colour. Actually, unless you really know what you are doing. Belgian 100 octane burns with a different colour to the 98 octane I use up here, so everybody peering intently at plug colours are really only confusing themselves. Probably best ro find a local 2 stroke racer and ask them (apart from the fact that 2 smokes colour their plugs with the oil they burn, so that’s probably not a good idea either
And lastly, its a Really Good Idea to do a bit more testing at home before flogging the bike down (up?) the main straight….
Sorry for the very long post, but some may find it interesting, and of course I’m open to other suggestions as t what went wrong.
