850 Shakedown Run

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Aug 11, 2006
Hi Folks-
Finished cleaning, greasing and checking the iso's on the '73 850 this morning and got the wild hair to ride it to town (about 20 miles) for a checkover run. Glad to say it made it with all the parts it left home with and ran surprisingly well! Bit fat in the midrange and it does have a little blow-by, but in this case the smell of burning Castrol in the morning smells like VICTORY!
This is a machine that sat neglected for some years and has had a new wiring harness, rear axles, bearings and brake drum, rubbers throughout, Boyer ignition, coils, and all the odd bits that are needed to bring a derelict back to fighting trim. Can't think of a better way to spend a couple of weekends! Now for the paint to bring it back to shiny glory. Still leaning toward Fireflake Blue or that non-stock metallic Maroon.
Nothing better than that first successful ride (You know, the one you don't finish up pushing the machine!) YIPPEE!

Kansas, America
'73 850 Roadster, et al............
sounds good.. I just finished a 4 hour push home, I think there is something wrong with my boyer or sparkplugs. I am a young guy, and just pushing the bike home up hills tired me out. Time for some water.
Oh, man! I feel your pain! My last push was 5 miles with a 441 Shooting Star. At night. YUK. Heck, I was a lot younger then, and it wore me out. Good luck with your gremlins.

Kansas, America
'73 850 Roadster ..............
I love to own the bike, and I could never get rid of it, but I let off a lot of swear words towards it today. After looking over the whole bike and troubleshooting it, I found out that one of the petrol taps had clogged up... good luck with your 850.
Hey Mike,

Glad to here u had a successful mission. I have a 74 850 project that is so near to the finish line, but yet so hard to motivate myself to finish.
Thanx for you post it has given me more impetus to complete the beast.

The fireflake blue sounds good, especially with silver decals. My 74 is in a Tangerine Orange substitute with black decals.

Cheers Richard

Sydney Australia
NateC said:
I found out that one of the petrol taps had clogged up...

Short question...was this a brand new petrol tap? Or just that you had not cleaned the tank out for a while?
Anyone had problems with new petrol taps? I have and I am curious if anyone else has. If someone responds with a "Yes"...which will give me the feeling I'm not suffering from some flashback... :cry: and I will get up the nerve to explain in more detail..... :wink:
It seems to be a old one, very old. I am pretty sure it was a replacement at one point, but am not sure of when, perhaps back in the 80's. I haven't cleaned the tank in a while, so that's what I am going to do today. There is no fuel getting to the carb, nothing in the lines.
I just come in from my first run tonight,
not as brave as you, only went 10 miles
but made it back.

Its been a long time since i rode it and
then only a total of 200 miles before
the complete pull apart.

I found the ride quite bumpy at the
rear which has Hagons. is yours the same?

74 850.

Got off work, fired up the 850 and headed West only to have a horrid cutting out and generally ugly-running machine. Turned tail and hi-kneed back to the office where I cleaned the float bowls (again) and jet stacks out. Cleared up the immediate symptoms but something is definately amiss. During the 20 mile ride back to the farm, I got a moderately wet right leg (OIL!!), some cutting out and generally running poorly. Seems to run well when cool or when the engine is cold, but heat her up and it's real horror-show. Waited a couple of hours after getting home and kicked it over- it ran well, so no catastrophic internal mayhem, I think. Keep in mind I've resurrected a garage-corner derelict, with all the usual new fluids, adjustments, clutch cleaning, etc.. The oil on the leg I believe was simply awful oil feed lines, but the "some blow-by" is a bit more than that, I'm afraid. nothing that can't be overcome with a top-end job at the most, and God knows it's due anyway. As far as ride, the forks are ok, new seals and no appreciable slop, the rear shocks are the originals, rides well in my opinion. Removed all the external ancillaries last night in preparation of popping the head off for some exploratory surgery. I'll know a lot more when I get to peek under her skirt, so to speak.
To hewhoistoolazytologin: Yes, i also have had faulty fuel taps. I ordered two brand new petcocks a few weeks back, they arrived, completely sealed and everything. I was anxious to put them on. I figured what the hell, might as well double check to see if they work, thank god i did. the reserve tap was good, the regular one however, I could not see light through it when i opened the valve, I was a bit shocked to say the least. It looked as if a rubber seal was blocking the passage, i tried 120 PSI of compressed air, and it did not budge. So, i finally stuck a dental pick into the rubber seal, and it broke through the seal, and i could see light. They went on great, and work great, still curious as to what that blockage was, though.
Thanks for all the good wishes out there. I don't see major torment getting this one sorted. One thing at a time........
Jim, if you'd face the thought of possibly pushing a motorbike 10 miles through Glasgow you are indeed a brave man! :lol: Seriously, Glasgow isn't as bad as it's reputation. Worst thing i saw there were a couple of VERY "happy" Celtic fans singing their rendition of what all the Rangers and their fans should go do with themselves(!) Best chip shops in Britain, too--Just ask a Glaswegian!

Hi, reference kanlimey's problem

"Seems to run well when cool or when the engine is cold, but heat her up and it's real horror-show"

I cured a similar problem last weekend, turned out to be the fuel filler cap vent hole was blocked, causing fuel starvation after about 20 miles of riding due to the vacuum build-up in the tank. A quick re-drill of the hole cured the mis-firing beast a treat!. Might be worth a look.

Hi Folks-
Found what I believe is the root of the problem. Got out my trusty modified Craftsman wrench (Farm Tech Tip--For the head nuts on the underside of the head, if you aren't fond enough of your Snap-On man to pay him $30.00 for a wrench or you don't want to wait to order one-take a worn-out 1/2 inch wrench and file across the box end -ring spanner- flats with a small triangular file until it fits a head bolt--they're the same size, and grind a little off of the outer ring. A 13mm might work as well if you're short on US size tools.) and had the head off last night. Immediately obvious problem--blown head gasket. The long nut on the underside of the right side was AWOL completely, and the rest of the bolts/nuts weren't torqued to specs. I believe there is an oil feed through the head gasket on that side, and it looks like the oil was entering the cylinder and blowing out the side when warmed up good, fouling the spark plug, and generally spreading hate and discontent. Piston tops look good, valve heads mildly carboned. I imagine someone in the past had the head off for service and got fruatrated when the compression problem arose (Just a guess, my crystal ball broke). All in all, a happy moment when I found this, but I'll have to dig deeper and check the valves for sealing, look over the cylinder walls, etc.. On cursory inspection it looks straightforward, though, and it even has a copper head gasket (undamaged miraculously!) If everything checks out it could be running again this weekend (Knocking wood with my rabbit's foot crossed in my fingers) Now if only Biggles would show to help hold those pesky pushrods up...................

Thanks one and all for the kind replies!
Kansas, America
'73 850 Roadster (Gonna paint it white and dub it "Snowball"-ok, I'm kidding) and a dozen other 2-wheeled Brit masterpieces
to 72fastback....

Reference Petrol taps:
Received two new ones from a big supplier in England and installed both of them. After a couple of runs, from a cold start but with a warm up, the bike started to pop all the way down the hill, and it just didn't take gas well at departure. All symtoms disapeared after a couple of miles. Noticed that the tickling of the carbs at startup took up to a half minute, to get them to overflow...not normal at all with the old petrol taps. Symtoms started to bother me and something told me to look for fuel filter blockage.

Undid the gas line connection and drained the gas into a canister. Took one and a half hours to drain five litres of gas out of the tank...it just dribbled...really not normal. Removed taps. Found both were, as you described, blocked by the rubber seal inside the petrol tap. Pulled apart. put back together several times and watching from the bottom hole, as I turned the taps on and off; after a couple to times, each tap gradually had forced the rubber seal to deform and close off the exit hole. Got tired of this and pulled them apart again and determined that the spring washer that puts pressure on the rubber seal is way too strong and clipped both out with diagonal cutters, put the taps back together and naturally them turn a lot easier, but the seal doesn't get deformed and block the gas any more. Also...the brass center piece , with the hole in it, was not counter-sunk, so every time you turned the tap, the brass ripped up the rubber seal...I filed and dressed the holes so this wouldn't happen further.

End result, I have new taps that are so beautiful and shiney, but inside the rubber seals are cut up and will leak soon. They are designed so crappy, that they were nowhere worth the ten pounds they cost apiece, and will have to be replaced some time soon. But due to my rebuilding of them, they at least won't burn my valves, or leave me stranded with a full tank of gas. I telephoned and addressed the problem with the supplier, but he had little interest in such niceities as to whether they were well made or not. I didn't try to return them, as I had butchered them, but certainly won't buy such crap again, in six months, when they need to be replaced....

Anybody else got these things installed? Nice chrome, look original, nut on end thread, that allowed them to be installed straight...good looking things....watch for extra long tickling times, and gas-starvation/popping exhaust.

I use those "BAP" taps. Don't look quite original but last for years without leaking. (Late Bonnevilles had them, I think).


The drilling in the cylinder is just a drain but most oil should go down the pushrod tubes. It might be worth shining a lamp down to check that your cam followers are the right way round (chamfer to the front) as this helps drainage.
Hi Folks-
The plot thickens! Had the 850 back together Sunday and went for a short ride. BLISS! Ran super, pulled like a freight train, vibration minimal.........until I turned to come back home. Popped, spat and was generally unpleasant to be on. The wet leg is cured, annealed the head gasket well, torqued the head properly and worked like a champ. Still have some slobbery Amal blues and a bit of blow-by that I don't care for, went through the parts bin in the chicken house (yes, I keep parts in an old chicken house), found two more sets of 932's of the correct number and am waiting on an order of needles with a side of viton float needles and needle jets. I've picked the tightest set to overhaul and use with the new bits. Bores look fantastic so a new set of Hepolite rings are on the way. I'll pull it down again and slip the new parts to it. Should do the trick. (Famous Last Words!) When I drain the tank I'll certainly have a peek at those taps, they are suspiciously new and could be a part of the overall problem! Those cam followers will be looked at as well when I have the cylinder off for the re-ring.
And something completely different- been talking to the local go-faster car racers, and they came up with some braided stainless oil pressure gauge line that they plumb their cars with. Sounds like the ticket for the rocker feed line, huh? Watch this space. One thing at a time!
Thanks one and all for the kind words and advice!

Kansas, America
Nortons, Triumphs and one lonely BSA
Hi Folks-
After a Scout campout that turned into a washout because of a tornado watch (In September, of all things!!) I got out and tore into the '73 again for the re-ring. As an aside, wouldn't it have been grand if Norton had lasted long enough to try an 8-valve setup? How'd you like to try to hold up THAT many pushrods while removing the head??!?? Teardown went well, heck, all the threads were cleaned up last time. Got the cylinder off (Farm tech tip---make a long "U" shape out of 1X2 lumber and clean it well, slide it under the pistons to support them and keep them from banging off of the front lip of the crankcase) and removed the old rings, honed the cylinder and.... had to go get a sparkplug gapper to measure the old ring gaps! It was huge! How about 47 thousandths?!? The oil rings barely peeked out of the ring grooves. Odd thing, it showed 135-140 pounds compression, cold, off of the kickstarter. Must have been all the oil in the cylinders, huh? New rings showed 12 thousandths, high end of tolerance, but for this rider, it will be fine, I reckon. I'll bet I see a lot less oil consumption and more power as well. Head checked out fine last time, held gasoline in the combustion chamber for 30 minutes without seep into the ports, but I was considering new valve guide seals just for G.P. Any opinions? Is it worth the time taken to remove the intake rockers?

Kansas, America
73 850 Roadster with new Hepolite rings
Not a bad practice to replace the seals. If you have the rocker extraction tool and the valve compresser. When you have the intake rocker shafts out you can drill them out with a 1/8 drill. Then you can delete the crossover oil line.
Hi Folks-
Yep, I did go ahead and change the valve guide seals just as cheap insurance. Dug through the parts bin and re-discovered a full engine seal set that I've had for a decade or so and forgot(!) Worked out very well, didn't have to pull the rockers to change out the seals. "C" type valve spring compressor, pulled the center stud for the intake rocker cover for clearance, snapped the retainers out and pulled the springs and valves. No problem. I've read references to the drilling of the rocker shaft to eliminate the crossover but am ignorant of the exact process. Please elaborate, this sounds like a very sensible modification. Less fittings, less potential leaks! Thanks!

Kansas, America
73 850 Roadster with new seals
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