Weird loss of power and sound

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Expat
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Re: Weird loss of power and sound

Post by Expat »

More complexity here showing my method to check settings. TDC was established using DTI which was removed and this set up substituted, first measuring to piston at TDC as shown in the pic, then moving piston back down then up, still on the firing stroke, to a position set by adding the initial TDC measurement and 0.437 inch together. My first timing setting was the same, ie points separating at the same position.
IMG_1548.jpeg
Normal service can be resumed and I’ll try not to make my posts so complicated and complex in the future if that helps. :lol:
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SPRIDDLER
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Re: Weird loss of power and sound

Post by SPRIDDLER »

Expat wrote: Tue Sep 12, 2023 3:46 pm Well, the last thing I wanted when asking for suggestions and opinions of how to get around an issue that confounded me initially was to initiate such an intense debate.
Cuh! That will never happen here. ;)
.......... as a tool/instrument maker with over fifty years experience, it’s in my nature to sometimes work this way
As a bodgemaker with over fifty years experience I can only dream of such expertise and equipment.

So if you hadn't changed anything except the rebore and piston since the bike was last ridden what was the problem as I'm still not clear whether you've solved it or not. :?

If I may be so impertinent, may I point out that the terminal connected to the black wire at the points looks in need of attention.
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Re: Weird loss of power and sound

Post by Groily »

[quote=SPRIDDLER post_id=252433 time=1694536490 user_id=85187
If I may be so impertinent, may I point out that the terminal connected to the black wire at the points looks in need of attention.
[/quote]

Saved my being impertinent Neville! LT live about to break off by the looks of . . . the bullet connector needs re-soldering with heat shrink or whatever to shield it properly. Classic misfire / dead short in the making there.

Like you, be interested to know whether the original timing was out. I think it probably was, or the cam had slipped quite a lot subsequently, as they do sometimes. Nice clean tapers, is what's needed, and moderate force with the scrooge on the axial screw.
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Expat
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Re: Weird loss of power and sound

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Give those men a prize!! You pre-empted my next question, spot the potential failure point. :roll: :lol: Yeah , I really must do something about that.

I honestly don’t know what happened here, other than it could be blamed on the hobgoblin that hides tools when your back’s turned, or spirits away that nut or washer that was definitely there ten seconds ago. I would bet all your money that the timing was correct before strip down and it’s definitely correct now.
When I started this topic I included pics of the ‘zorst valve and seat and the original piston and following the advice offered by you lot, bought a new valve and piston kit and had a 0.020 inch o/s rebore and hone carried out.

Shortly we will find out if the old girl has had a new lease of life……….or if the timing needs adjusting. :shock: :lol: :roll:

Seriously, thanks all for your time in this, hmm, adventure. Steve
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clive
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Re: Weird loss of power and sound

Post by clive »

Expat wrote: Tue Sep 12, 2023 4:17 pm ..next pic shows there was no more adjustment available to set timing correctly and align those two black sharpie lines that denoted correct position originally. Ignore the scratched lines done by p o. Steve

IMG_1544.jpeg
I was going to keep quiet but I cannot help but comment. I assume by the black sharpie line you mean the black marks. I cannot see how the two marks you have could ever have lined up as they would have obscured the screw hole. However there seems to be a trace of a mark further round the correct side of the screw hole. Not got wiped off has it?
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Re: Weird loss of power and sound

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Clive, like you I was going to let this pass but what can I say? With new piston etc fitted, timing was way out compared to previous setting when bike was running. When I came to reset the points cam by moving it on it’s taper, the locking screw was still tight and I had to use a release screw to break the taper fit. How could it have slipped ?
Pics below show

Cam position relative to points heel with ATD wedged at full advance, timing set at correct position
IMG_1549.jpeg


Cam position relative to points heel with ATD at full retard
IMG_1550.jpeg
Subtle difference but to be expected I suppose. Got the head and rocker box on today, checked timing using rod down plug ’ole, a brilliant, effective method I coincidentally learned from a Spriddler post, and it came up just right!
Best result of all, she fired up third kick and in spite of loose rocker clatter which I later adjusted out, settled to a lovely even idle, better than ever before with much higher compression noticeable on kicking over. Will post a short video as I’m dead chuffed with the end result of the job overall. Never had an engine rebored before. :P
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Re: Weird loss of power and sound

Post by Groily »

Good it's running again, and much better by the sound of it. The points backplate position looks as one would expect now, with decent movement available both ways. A 15 thou gap when on the cam, a repaired low tension wire, and you should be fine for ages.
A bit dull for you having to run the new piston in (JPs appreciate care in the early miles as they expand a lot more than the originals, hence their need for a generous rebore clearance), but it's a small price to pay for having a decent motor.

Going right back to the very beginning and your first post, the symptoms you described were absolutely typical of the timing having slipped (as per the initial replies) although the 'consequences', if not already present to some degree, were a bit direr than usual. It was probably close to needing the rebore etc anyway though, if it's any consolation!
The cam ended up fast on its taper again after it all cooled down. I don't think that's unusual, though there's 'tight' and there's "tight".
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Re: Weird loss of power and sound

Post by Expat »

Cheers for the heads up re running in Groily, only went a few hundred yards today so plenty still to do.
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Re: Weird loss of power and sound

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Chapeau! 🎩
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Re: Weird loss of power and sound

Post by EddieDay »

Steve, Good to hear that the bike is back together and running well. I am in the reassembly process with my M18S now. I'll put an update on that thread when she is running.
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