Cams and ignition timing

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Cams and ignition timing

Postby Matchymarty » Tue Jul 31, 2018 8:10 pm

Hi all,

My G80CS '55 longstroke has SH cams in it. Just wondering, does one need to do anything to jetting or ignition to best serve the cams?
Is ignition timing set to 1/2" BTDC for all cams?

I'm considering putting 'standard' cams in the bike. Seems for the riding I do - mostly rally's where 45mph is cruising speed and 50mph is max speed, the bike is never happy.

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Re: Cams and ignition timing

Postby Andy51 » Wed Aug 01, 2018 8:47 pm

Hi Marty, I run a '54 18S fitted with SH cams and 8.5 to 1 piston. The carb settings in the Parts book are the same for all 500s, as are ignition timings, so my bike is set to 'normal' settings/timings. It is slightly less flexible than my standard G80, but runs well at all except very low revs, and is happy down to mid 30s in top gear (G80 is happy to high 20s) so is good for normal club runs. Sounds as if your bike is not set up quite right - what carb is fitted? I find the 18S has better acceleration, cruises happily at 70 mph, and is very useable but it does make a lot more noise! Cheers, Andy

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Re: Cams and ignition timing

Postby Matchymarty » Thu Aug 02, 2018 10:43 am

Hi Andy,

Cheers for the feed back. My '55 CS has a 389 Mono with 400 main and 30 pilot, 106 , SH cams, and 'normal' timing and cam timing. That said, i've never checked the cam timing with a wheel. My piston is a 7.2:1 JP piston. Mag was done less than 500 miles ago.

I've seen 70mph, but only with a huricane behind me whilst riding off the side of a cliff. I can do 60, but no way I could cruise at 60, and 50 is comfortable, yet, ant hills upset it and I have to apply a good dose of 'welly' to get over them.

Put it like this. Father in laws clapped out '49 350CS, with bad valve clearances, flogged out concentric, untouched mag, bad fuel and a lot of rattles, keeps up with me and can also go 60 and cruises at 50. I have to really get under the '55 500CS to pass him going up a hill.

Is there any possibility that my cams may have been re-ground or fiddled with to cause such issues? Cam timing is set per book recommendations, but if they've been re-ground, would that upset things?
I'm really at a loss if you say you can comfortably cruise at 70... no way mine could even hope to do that. When I cooked the second last piston, (i've cooked 4 in 6500 miles) my engineer suggested it was way too lean (260 main 30 Pilot) and we tried a few mains from 360 to 400 and settled on the 400. It feels like it bogs a little when opened up hard, so maybe, a 380 might be better, but, until I put the 400 in, I'd never seen 70 mph before, and it struggled to even stay at 50 along the flat.

At my last rally, I cooked my 4th piston, and top ring stuck. I managed to get it fixed at camp, and rode it the next day, and that was on the 400 main. That, was what the engineer told me was caused by being too advanced. Hence why I run it a bit retarded now.

So... I dunno. This bike continually tests me.


Andy51 wrote:Hi Marty, I run a '54 18S fitted with SH cams and 8.5 to 1 piston. The carb settings in the Parts book are the same for all 500s, as are ignition timings, so my bike is set to 'normal' settings/timings. It is slightly less flexible than my standard G80, but runs well at all except very low revs, and is happy down to mid 30s in top gear (G80 is happy to high 20s) so is good for normal club runs. Sounds as if your bike is not set up quite right - what carb is fitted? I find the 18S has better acceleration, cruises happily at 70 mph, and is very useable but it does make a lot more noise! Cheers, Andy

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Re: Cams and ignition timing

Postby SPRIDDLER » Thu Aug 02, 2018 12:33 pm

Matchymarty wrote: I can do 60, but no way I could cruise at 60, and 50 is comfortable, yet, ant hills upset it and I have to apply a good dose of 'welly' to get over them.................. When I cooked the second last piston, (i've cooked 4 in 6500 miles) my engineer suggested it was way too lean

Something fundamentally wrong there. Does it have standard gearing - g/box and rear sprocket? Not that undergearing would make hills a problem.
I'd double check that the timing was correct at either 7/16" or 1/2" BTDC on Full Advance and leave it at that (either will be fine; a 1/16" difference wouldn't have the detrimental effect on performance/pistons that you experience) and then look elsewhere. You shouldn't have to 'run it a bit retarded'.
Try a 380 main jet ( :? ) and ensure you have the correct slide. If there is a fuel restriction this will weaken the mixture on large throttle openings, limit the top speed, overheat and consequently stuff the pistons. Check the fuel filter(s). Try opening both petrol taps to increase the potential flow rate.
Flying kites here, but a pal very recently had slightly similar trouble and (long story cut short) the zorst front pipe was too long and ended (unseen obviously) about 3mm from the silencer baffle plate, hence the engine had too much back pressure and was being suffocated at larger throttle openings.
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Re: Cams and ignition timing

Postby Mick D » Thu Aug 02, 2018 3:47 pm

Hi

Start with the obvious:

What colour is the plug?
Has the exhaust blued where it exits the head?
Is there a lot of carbon in the tail pipe?

In general:

An over rich engine will be low on power, create soot in the tail pipe and the plug will be matt black - the richness can dilute the oil lubricating the upper cylinder leading to a seizure.

A lean engine will create more heat leading to the header pipe bluing and the engine seizing, (though a lean engine doesn't tend to exhibit power loss so significantly).

Regards Mick

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Re: Cams and ignition timing

Postby Matchymarty » Thu Aug 02, 2018 9:21 pm

Spriddler,

Thanks for comments.
I've triple quadruple bazillionuple checked timing and is spot on at 1/2" BTDC @ Full advance.
My exhaust header pipe is the 'narrow' diameter one that flares to fit the head. It is the smaller diameter one as it has to fit over the foot rest and under gearbox. Strangely, my '56 has large diam pipe all the way, but has an AMC box so different fit i guess. The '56 pipe does not fit on my '55, I've tried. My silencer has a baffle, but previous owner cut a big hole in it so, basically it's open. I'm not sure if the header blues, as it is ceramic coated, and does not show anything, and there's too much oil residue in the pipe to know if there's carbon in there or not.

I'm pretty sure it is running stock gearing. I've checked this before a while ago, but will check again over the weekend. I know it doesn't really like taking off from stand still half way up a hill. 18T Engine and 16T GB. Again, I'll check this.

Pretty sure I've gone over the Carb, as I went though this with my engineer, who had lists of carb settings that I'd never seen (from the factory). My manual states that 'all spring frame comp models' were fitted with TT carbs, but does not state settings. It does say though, the rigid frame Comp models had 389 with 260/30/#3 slide/106 and central notch. My 389 is set to that, and was, but my engineer said it must have been running too lean, so thats when we ended up with the 400 main. It does go a lot better than what it did with the 260.

I run a bosch clear tapered fuel filter on one line and only usually open one tap.the filter is always full, so wouldn't have thought there would be restriction in flow? I did have vapour lock issues once, but then drilled out the hole in the fuel tank cap, and never had that issue again. I do run a small 'pancake' air filter from Hiscocks too, but one would think this would only richen the mixture. I could, and might however, run it without over the weekend to see what happens. (@ full advance)

Strangely, after the rally this weekend just gone, my return ride to camp, the bike missed a bit for around 1/2 a mile, came good, then I tested at full revs, under hard accel, and it missed again multiple times. Since, this week, I checked timing again, and looked in the plug hole to find little flakes of shiny metal on top of the piston. Not sure where that came from, and don't know if it's sinister or not. Plug also has some foreign particles on it.

The bike does smoke on over run, and I've never been able to stop that since owning it. I've shut off the valve feed, had guides checked by a head guy, re-lapped etc... and obviously had 4/5 rebores and pistons with new rings. C'Case breather works fine, actually spews oil everywhere, and does drip from there when parked.

The bike uses loads of oil, always has. I can't seem to get to the bottom of that either. When I say loads, I mean, 100ml per 100 miles. It'll also smoke if I gas it and change gears, but not really smoke while cruising along.

Dunno. I seem to be more hairless since owning this bike. It kicks my arse at every opportunity. I try and do everything right, but it just keeps kicking me.

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Re: Cams and ignition timing

Postby SPRIDDLER » Thu Aug 02, 2018 10:04 pm

Duplicated.
Deleted.
(It was late :roll: )
Last edited by SPRIDDLER on Fri Aug 03, 2018 8:13 am, edited 1 time in total.
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Re: Cams and ignition timing

Postby SPRIDDLER » Thu Aug 02, 2018 10:47 pm

Hmm. It's a bit late at night to give proper thought to your detailed descriptions but at first thoughts:
In the second pic of the piston it looks as if the plug hole has been Helicoiled.............?
In the third pic the zorst port in the head (or at least the filler of black todge sealant) seems to be considerably larger diameter than the down pipe that's fitted.
I may be going down a blind alley and it could be an illusion but the pipe seems to have a diameter more like a 350. I'm not particularly familiar with the CS version of the G80 but I can't imagine that there 'should' be such a step between the two and (in theory) would make jetting the carb difficult as the engine/cams are calling for the correct amount of petrol/air mix but can't get rid of the burnt gas quickly enough........maybe those in the know can comment on the diameter of their CS pipes.
The smoky zorst and high oil consumption needs further thought. Maybe the misfiring you experienced was due to the plug fouling?
And as for the 'metal flakes' ...... :? Could they in fact be bits of the spark plug ceramic central electrode insulator?
It might be useful to know if you can pick the 'metal flakes' out with a magnet (steel flakes) or not (alloy or ceramic flakes).
I need to sleep on it.
(Edited later after putting me teeth in to soak. How sad is that? :roll: )
Last edited by SPRIDDLER on Fri Aug 03, 2018 8:17 am, edited 1 time in total.
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Re: Cams and ignition timing

Postby Matchymarty » Thu Aug 02, 2018 11:00 pm

Yes, the header pipe is probably '350' sized, but flares at the engine head. I thought this was weird. However, Armours, even have a pipe for the 500's like this. I suspect it's for the models with over foot rest exhausts, with B52 gearboxes. As i mentioned, the full diameter pipe does not fit between peg and g'box.

See attached photo - this is typical of how my engine runs. Head gasket always leaks oil - no matter how tight the bolts are. Also, oil is always present at plug hole as if blow by is evident. Strangely, after the last ride, the oil marks on top fin near plug, seemed to be 'diluted' as if by petrol or something, giving a more 'ring' effect, rather than an oil pool to an edge like is shown in this photo. So that's a new thing.

The plug holes doesn't appear to to be helicoiled to my knowledge. I'll check tonight though.

Yes, the plug may have been fouling, it is quite sooty, together with the oil consumption, that could be something. Especially as first lot of mis-firing occured whilst trundling along at 45mph for a little while. The slight retarded ignition may have contributed there too.

I'll check the exhaust header length and diameter tonight also, together with the flakes on top of the piston.

Sometimes I wish I didn't sell my G80S. That was a great old thumper, that just mosey'd along without any issues. I have 55 and 56 CS's, and they are both nightmares!

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Re: Cams and ignition timing

Postby SPRIDDLER » Fri Aug 03, 2018 9:02 am

Matchymarty wrote:Yes, the header pipe is probably '350' sized, but flares at the engine head. I thought this was weird. However, Armours, even have a pipe for the 500's like this. I suspect it's for the models with over foot rest exhausts, with B52 gearboxes. As i mentioned, the full diameter pipe does not fit between peg and g'box.

I guess that's how it should be then. I've just found a photo in the archives of a '56 Mod 18CS and there does seem to be a reducer where the pipe joins the head:

18CS zorst 1956.JPG


The plug holes doesn't appear to be helicoiled to my knowledge

Since you have considered and addressed all the usual things my clutching at straws thought was that if it has been Helicoiled and a tang of the insert glows in the combustion chamber it could cause pre-ignition, spoil performance and cause piston damage.


I've often noticed an oily weep at the head joint and around the plug hole on bikes that otherwise regularly run fine.

I have 55 and 56 CS's, and they are both nightmares!

:headbang: Do they both have similar issues?

Well, now we seem to have come back to where you started. :?
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