New Member -Weak Spark Troubleshooting-

Classic Norton Commando Motorcycles.

New Member -Weak Spark Troubleshooting-

Postby montana850 » Thu May 05, 2011 8:32 pm

New Member -Weak Spark Troubleshooting- First of Many Questions.

Hello my name is Mitch and I live in Missoula, MT USA.
The Background:
I was recently willed (6 years ago) a 850 Roadster that was half in the basket. The story goes my father was a Norton dealer in the 60's and 70's and turned a wrench on them until the mid 90's. He had this bike sitting around with a master plan in mind. I vaguely remember where he got the idea but I think it was an old CycleWorld. The plan was to fit the 850 with a 750 Combat cam in the interest of power and curiosity. He had instructions of what had to take place to make this work ( I don't know where this napkin went) like machining the pistons to handle the extra valve depth but aside from that I do not know. 6 years ago his health failed him and I ended up with a bike that was in various states of disrepair. Connecting rods sticking out of the crank with gearbox attached while the Cylinder, Head, Pistons (machined for valves) Valves, Carbs etc sitting on the bench. I lashed into the project like a sloth as time permitted and have finally after 6 years put it back together using a workshop manual. The only thing I've purchased was a TriSpark points replacement. The pile of extra parts is small and looks like it came off of a Ducati 350. Okay enough the the back ground.

I followed the TriSpark instructions and was getting great spark to both plugs and son of a gun after tickling both carbs the old beast sprang to life. Ran very rough but I didn't hear any metal on metal noises. I connected a stobe to set the timing and the light was very bright. After about 3 minutes of dinking around the strobe light started to get sporadic and eventually went out about the same time the engine quit running and would not fire again. I once again set the Trispark statically with no luck. The battery operating the stobe is good but I tried another just to rule it out. Same symptoms. Bike battery is fully charged. Head light is very bright. Spark is very weak on the left and non existent on the right. Not sure what happened. I should've paid more attention when the old man was showing how these things work. I have a few more issues to deal with but i figure I better get this worked out first.

Thanks in advance for any suggestions that might get this beast rolling.

Thanks,

Mitch
Last edited by montana850 on Tue May 10, 2011 8:59 pm, edited 1 time in total.

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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby Tim_S » Thu May 05, 2011 8:56 pm

Start from the beginning and check all your connections. If nothing changes spark wise, switch plug wires and see if the weak side moves to the other side. When using the strobe timing light use a separate battery from the bike. They tend to work better sometimes. Report back with your findings...........


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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby pete.v » Fri May 06, 2011 8:51 pm

Sounds like the coils went bad. Are they new, old, any spares on the shelf. Look into a 5 ohm Dyna coil if replaceing. You got that nice Trispark unit, old coils may be your weakest link.

You say th battery is full. 12.5 or better full? The timing light will stop, of course, cause there is nothing coming down the plug wire to conduct.

Did you put in that 2s cam? Machine the pistons? The other thing to do would be to shave the head. 2s's like higher compression which is not readily available in 850's, and may not give any power improvement with out it.

Jetting may be needed also, raising the needle a notch and poking the mains.
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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby rick in seattle » Fri May 06, 2011 9:00 pm

The symptom (weak spark at both plugs) points to a problem on the coil primary or, dare I say it, the TriSpark. The coil secondaries, plug lead, caps, and plugs would have to crater on both sides at the same time to cause what you report. Most EIs have a troubleshoot mode (usually disconnecting and reconnecting a wire) that induces sparks in both plugs. Insure that the plug ground electrodes are firmly grounded to the head for this test.
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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby ntst8 » Fri May 06, 2011 11:27 pm

Trispark have a trouble shooting guide on their website which may help, at least to discount the Trispark as being the issue.
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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby montana850 » Sat May 07, 2011 2:27 pm

Dang you guys are awesome! Thanks for the responses.

I swapped the plugs for new and am getting good blue spark what the hell. Not sure what would foul both plugs at the same time. A steady diet of too much gas? Waiting for a buddy to get over here to run the strobe for me before I attempt to fire. I went back though and verified connections as best as I could.

The coils are an unknown they were sitting on the bench next to the partially assembled bike. Is there a way for the average man to test them without fancy gadgetry? Battery was was reading a bit less that 12.5 more like 12.1. It has sense spent some time on the charger. I did not put that cam in. I did install the pistons and they had been machined with cutouts for the valves. I'm not sure if the head was shaved . How much does a guy dare whittle off? Any idea how much clearance would be required for the piston and the valve. I did a very primitive test with some silly putty (I'm not kidding). There seemed to be a bit less then an 1/8 of an inch clearance. I was sweating bullets when I first rolled it over half expecting an explosion. Will do on the needle and mains.

Once again thank you all for your time. I will give it a shot this afternoon and report results.

Mitch out

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Re: New Member -Weak Spark Troubleshooting- First of Many Qu

Postby montana850 » Tue May 10, 2011 6:10 am

Minor setback. Fired yesterday with new plugs and needles in middle slot. Ran okay at the 28 degree static setting. Was getting two marks with the strobe ranging from 25 to 30. Looked like oil was circulating into the oil reservoir. Roughly 3 minutes in lost right cylinder then the whole works. Compression is now pitiful at best. No loud bang or grind. Fearing catastrophic failure. Will start the disassembly tonight and report when I know more. Does anyone know of a good resource for a new cam? Thinking I might want to take the combat cam out of the equation.

Thanks,

Mitch

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Re: New Member -Compression issue

Postby montana850 » Tue May 10, 2011 8:58 pm

Figured I better get to the bottom of this compression issue.

Many apologies for wasting anyones time but it appears that I've never had fire in the right cylinder. Decent spark and a wet plug but no life. No wonder it sounded rough. I pulled the head/cylinder and the right side is clean as a whistle. So much for the hand over the pipes test. Not sure what to do at this point. Rings look good, cylinder wall looks good, piston looks good, valves appear fine (not visually bent or stuck), everything moves as I would expect when kickstarted is rolled over. I had compression at one point with one cylinder firing. Can valves or a timing chain lose their way through the course of operation? With the combat cam in the 850 is there anything else that should've been done besides cutting the notched in the piston? Is there a way to test if the valves are closing enough at the correct time to create compression?

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Re: New Member -Weak Spark Troubleshooting-

Postby hobot » Tue May 10, 2011 11:07 pm

Not good practice to use bike battery to power strobe light as alternator may not keep up with just ignition voltage needs while mostly in idle mode. When I did this bike got rough as hell when V dropped and light blinked out of synch, then quit. Put centerstand on thick carpet cushion to stifle the Cdo dance away.
Good as new fangled electronic ignitions are they can and do fail in half ass ways not completely as might be expected. So leave that in back of mind while diddling other things first like coils. 12V coil ohm should be ~3.6 and 6 v ~1.8 ohm. I don't think electronic ign. need the ballast resistor in line so check that and by pass it.
Before disturbing the head do compression tests and leak down tests for both a sense of Comp Ratio and sound of gas escape out carbs or headers if valve issue or breather if rings.

The 2S cam is a great cam profile most all the other cam just alter a bit from its base line. But 2S cam needs like 10 CR to feed well especially in idle and mid range. Combat heads shimmed .040". Risky to go more and must compensate the squish contact rim. Thinner gasket from Jim Schimdt might be next step but remember this alters the rocker contact on valve stem centering so may want to shave pushrods to match. Combats like 28' full advance but don't know in 850. Must diddle that to find out.

Can not trust factory cover degree dial so must go by feel, ie: adv just short of kick backfire and retard enough no detonation on octane and engine loads. Degree wheel necessary to place TDC marks and 30' mark on Alternator stator and paint the correct alternator rotor line. Buy plugs in V8 packs as can't trust them right out the box and can foul up to short while getting bad spark and mixture dialing in.

I'd suspect that the 850 with 2S cam should come on cam lower than 6800 rpm it does in my 2 Combats.

Oh yeah should idle best 1.5 pilot screws out, if not suspect float level base line off. Time it first though.
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Re: New Member -Weak Spark Troubleshooting-

Postby montana850 » Wed May 11, 2011 8:40 am

Roger that on the bike battery for strobing. I’ll verify Coils. Check with manufacturer on ballast resistor. Compression test. I can trouble someone to give me a dumbed down step by step of the leak down test? It back fired once then fired on one cylinder at 28 degrees (factory cover). Would rotating clockwise be advancing? Pilot screws are set to 1.5 out. What slot in the needle should I be trying? What are the chances the 2S cam will work without machining, shimming or shaving? I still don’t get how I could go from compression to no compression without some sort of visible damage to the valves, gaskets, rings, cylinder etc… Where is the breather located?

Report coming shortly.

Thank you all again for the time and knowledge. You guys are awesome!

Mitch

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Re: New Member -Weak Spark Troubleshooting-

Postby hobot » Wed May 11, 2011 8:07 pm

Compression test is just sticking a gauge in plug and kicking over good with throttle WOT till gauge no longer rises, done with and w/o some oil shot in for sense of ring blow by.

Compression test short video.
http://www.youtube.com/watch?v=ovvXnd7A ... re=related

Leak down is trickier and a bit dangerous putting 100 PSI on piston, as will spin crank connected to rear tire so w/o nailing brake down and/or wood stick shoved in spokes in 4th gear, might leap right past you and take a finger with it.

Here's a video on air cooled push rod and DIY gauge regulator. New costs over $100 but might ebay one or rent one or wait on me to send ya mine. Air compressor required.
http://www.youtube.com/watch?v=GvG22YMOzUI

Open up rockers and see if all valves move as expected. If none move, not likely but would imply cam not turning. Valves not seating, make sure the last in set enough. Combat 2S is .008" intake and .100" exht.

Not likely but possible head gasket blew out towards the push rod tunnels.
Air would leak into sump same as ring but more so.

Breathers vary -but all factory ones vent to oil tank then that vents to outside
or yuk into air box.
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Re: New Member -Weak Spark Troubleshooting-

Postby montana850 » Wed May 11, 2011 10:52 pm

If a picture is worth a thousand words a video must be worth a bazillion. I will try these troubleshooting steps as soon as I get it back together. In a fit of depression and madness I pulled the cylinder off to inspect the rings more closely. Everything looks fine rings, pistons, cylinder walls, gaskets and even the valves were moving but I have to ask. How do you know if the rings are the correct size? It was a long time ago but I seem to recall these rings were not new compared to the new piston. Could this be throwing a wrench in the works? They do not appear excessively sloppy however, I'm not exactly sure what is acceptable.

I'll wait for word on what makes a ring or three permissible and then get it back together then start with the compression test, then the leak test. Thanks for the warning on the finger removal potential. That is very much in my wheel house of injuries.

One more thing. Does it seem reasonable to have the clip in the middle slot on the needle as a beginning baseline?
I tried to find this in the shop manual but was unsuccessful. Evidently they were not planning on a gen x spoon feeding.

Thanks for the knowledge!!


Mitch out

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Re: New Member -Weak Spark Troubleshooting-

Postby montana850 » Thu May 12, 2011 6:15 pm

Bent valve appears to be the culprit, ah sugar. Spare motor going in.

Thanks for all of the input. I'm far from out of the woods so I'm sure I will be in touch.

Thanks again,

Mitch out

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Re: New Member -Weak Spark Troubleshooting-

Postby montana850 » Thu Oct 27, 2011 10:18 am

Sweet Victory... Had the head done by someone who knew what he was doing, new guides and valves new rings as well and away she went. Truly a thing of beauty. Just in time for the snow to fall. God Damn it. Thanks for all the input!!

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Re: New Member -Weak Spark Troubleshooting-

Postby dynodave » Thu Oct 27, 2011 2:35 pm

If they knew you were running a combat cam, as part of the new valve job...they might have removed the valve spring insulators on the intakes?

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