commando 850 sulking

My money's with Hobot on a disintegrating cam lobe. :|

bluemax said:

[/My money's with Hobot on a disintegrating cam lobe. :|quote]

If that was so then why do I have a humungus crankcase blow by, see last post, with shop air in the sparkplug hole I got a gale out of the oil tank crankcase breather on the left pot and very little on the right pot (both tested at TDC).
If lobes worn = no lift = valves closed.
But thanks for your thoughts.

Head comes off tomorrow and all will be revealed.

Cheers
Peter R

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Did you rotate the second cylinder to TDC (closed valves) as i assume you did with the first cylinder (closed valves) ??

Absolutely
Actually took the hear off this evening.
Put my palm over the bore and good compression on the right pot and quite a deal less on the left hand one.
Barrels off tomorrow.
Pistons are Standard and no lip on the bore and not much wear.
Could be original, there is a letter B stamped plus STD.
I'm a bit sus about a raised mark on the left piston, tomorrow will tell more.
What brand pistons are people using these days and what brand rings.
I think I saw some post on JCC pistons but using some other brand rings.

Cheers

I don't remember brand, but I got 'em from Old Britts. Standard size; imagine my surprise when I cleaned all the carbon off the piston tops and saw the little ".020" stamped there.

First start up after installation I was (this time pleasantly) surprised by how much more "pop" I could feel in the exhaust pulses by holding a hand up behind the mufflers.

As I said, no issue since.

So here is the next instalment in why the Norton sulked

One should always trust their gut and the bigger the gut the more trust.
3 broken rings 2 on the left pot and one on the right.

Thinking about reusing the pistons not sure what brand they are but it look like they might have something that looks like AE cast inside the piston skirt.
I will dress the small bump (probably ingested something in its life span) on the left piston
Can anyone tell me the ring grove specs so I can see if they are worn.

Considering the break in the compression rings there is not that much blow by.
I did the ring in the bore check and got about 5 tho diff top to bottom. Will mic the bore to see what it actually is, but before I dissembled the pistons did not have much movement just a nice amount and it never had any piston noise or use oil.

Cheers

bluemax said:

Thinking about reusing the pistons not sure what brand they are but it look like they might have something that looks like AE cast inside the piston skirt.

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"AE" = Hepolite.

Pistons look real good considering the breakup. But why did the ring breakup ? And what's with the piston crown boo boo blemish left lower ? I'd just fit new Hepolite rings with a honing and hope for the best. Oil flush and filter too. And check magnetic pickup swarf too if fitted. :| Others with bigger wallets will say spend.

Yeh don't know why they broke up, but I think the piston ring groove may have something to do with it.
There is a distinct lip on the groove and if you look carefully you can see the shiny lip on the top groove and you can feel the lip with your finger nail.

Suspect maybe out of spec and rings flogged around and broke.
Blemish is a don't know as well I will blame it on the previous owner.
Long answer short is I just don't know, but lending towards shouting it some new pistons and rings.
You can't take your money with you when you go, can you.

A trick I used was to stuff some rag into the crankcase and use a magnet out of magnetron from an old microwave to slip under the cylinders as the pistons came out to trap any broken bits before they disappeared into the crank, worked a treat.

Cheers

Well in that case go for the new pistons ,rings and rebore costs. Ya can't take it with ya .. If in your position I would think about those costs then apply them towards the JS system . But it always boils down to money and hopefully not consulting the wife re: that stuffage. P.S. i'd still just fit new rings n' hone cheap n' easy if it doesn't work out just go into debt. That upper ring land looks acceptable ? -nothing bent but a better photo nice for all of us and of course measurements if you have such tools. If the new rings don't seat and use oil then pull out the credit card and feel good. Others will insist you $pend now.

OK used the only intact compression ring and checked the ring groove side clearance as best I could with a feeler gauge.

Top compression ring groove clearance 16 thou
Bottom compression groove clearance 9 thou

These piston now belong on the shelf with all the other offering to the motorcycle gods.

Just need to decide on what size, so off to the experts next week.

cheers

I don't think I've ever seen any engine break rings like that! I'm glad you decided to go the rebore route. Too many times I've tried to scrimp when thinking things looked "usable", only to have to pull it back apart to do it proper.

Has anyone had anything to do with Arion pacific Industries Pistons or know if they are ok.
I can source some with Hastings rings at a reasonable price but not sure about the pistons, can't find much on the web about them.

Cheers

OK the commando is no longer sulking.
New pistons, rings and a rebore has put a smile on its dial.
Compression dry when first assembled was 145+ per side, so should get even better.

Thanks to a local forum member who had some hepolite/JCC pistons and USA rings plus jets to recalibrate my carby, he knows who he is.
Many thanks and now to do the heat cycle run-in and re torque sequence.

The only trap I fell for was changing from a 3.0 slide to a 2.5 slide.
I had one in a carby I had lying around and stuck it in.
First startup was super rich and rough.
Was there something with the rebuild?
Nooooooo I put a left hand slide in a right hand carby didn't I.
One feel quite stupid.

Now to see how the recalibrated Mikuni goes.

Cheers
Peter R

Glad for your happy dance but 2.5 slides means opportunity to creep up on idea by hand filing a bit away at a time, which is old school hot rod standard procedure, though usually with a drill on the butterfly flap.

I will be interested to hear how you like that calibration.

Just going through heat cycles and re torqueing sequences.
Early indications are that the VM34 calibration is much improved.

A thanks to NorcomCycles for their advice and the supply of parts.

I would be interested to see what others have for calibration for their Mikuni VM34 on a standard 850.

My new calibration is
40 pilot
240 main
6DH3 needle
159 O-8 emulsion tube
3.0 slide
air is 2.0
needle set on middle slot
air screw set for best throttle response.

Would like to goto a 2.5 slide but the one I had was for the wrong handed carby.
Would like to richen the 0-1/8 throttle range and then lean off the idle a bit.
I thought I had another carby to try but upon careful measuring it turned out to be a VM32, damn hard to tell without measuring

This is the plugs after only a 20K city and Hwy run, a bit early to tell but promising as always black before recalibration.




the previous calibration was
35 Pilot
260 main
6DH3
3.0 Slide
159 P-5 emulsion tube
air 2.0
needle on the top slot
It started and ran well but always seemed to be running rich.

Cheers
Peter R

To my eyes those plugs look desperately lean.
But I haven't followed this closely, and didn't see your plugs before.
And didn't note which petrol you are using.
You don't say what plugs these are either ?

Your pipes are not bluing, are they ?

Cheers.

bluemax said:

This is the plugs after only a 20K city and Hwy run, a bit early to tell but promising as always black before recalibration.

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Thanks Rohan I would be interested in why you believe these are desperately lean.
Granted these plugs have not done a lot of K's and a bit hard to get a lot of info from them.
I cleaned these up as they were sooty from the last calibration and since putting the engine back together have only done a test run of less than 20 miles.
My understanding is with unleaded fuel you don't get a lot of colour, and comments to me from others is they can be scary clean compared to leaded fuel.
From my small understanding of unleaded plug reading is that the rim on these plugs are telling me it's perhaps a little on the rich side down around idle.
A change from a 3.0 to a 2.5 slide and then a lean off of the air screw may improve this (everything is interactive around the bottom end)
The plug might also be a bit too hot.
The earth strap is a light grey not white and light grey or light tan is about right I thought?
I will need the mag glass to see what the insulator is telling me down low as I believe the insulator is usually clear of most colour on unleaded.
These plugs are iridium and the electrode is quite thin and harder to read.
I actually have just come back from another test ride of about 90 kilometres and pulled the plugs after running at 100kph for a stretch and it is about the same as the picture.

The bike pulls clean and smooth right through the range no hesitation, no popping or backfiring on roll off, and not detonation knock at any engine load.
Idles about 800 rpm nicely and the air screw ended up 1 1/2 turns out.

But hey I'm open for any comment as I have a lot of trouble reading unleaded plugs, hence my interest in others mikuni settings.

Cheers
Peter.

If its not blueing your pipes, and the engine is not showing any sign of heat, then we probably can't argue with that.
But those are among some of the palest plugs I've seen on unleaded fuels.
Usually they go fluffy black at any opportunity outside of hard clean running ?