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Grant R26
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VBMWMO #8145
Toronto Canada and Long Island, Nova Scotia
Joined: 03/28/2011
Posts: 158

After 3000 trouble free km this summer, my lovely R51 started running roughly. I cleaned carbs, fresh gas, checked and double checked the points, gapped the plugs and high tension leads but still no better. Intermittently running on only one cylinder.

Today, as a last resort I replaced the almost-new spark plugs which had only 300 km on them; now it runs great !!!

Problem solved !

I installed new NGK B8 ES “long reach” plugs that Vech sent me specifically for the R51/3

I see now that the old plugs that I removed were “short reach” NGK B8HS

I verified that there is plenty of room for the long reach at TDC … so no worries there. Now I’m wondering about these plugs and nowhere in my prized Barrington Motorworks manual are spark plugs discussed.

I have a R27 too; Did I mix up my plugs and the short reach NGK B8 HS are for my R27 ? Perhaps both work and are interchangeable ?? (though I suspect not)

According to my “Spark Plugging The Classics” chart the HS appears to be a slightly hotter plug than the ES though perhaps not enough to matter?

Does anybody out there have the definitive answer or any advice for me on R51 spark plugs ?

Thanks !! Grant MacNeill
The Twelfth Fret Guitar Shop, Toronto

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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The "8" is the heat range, so

The "8" is the heat range, so they're both the same. The "E" is 3/4" reach while the "H" is 1/2" reach. The "S" defines the centrode dimensions.

If you have heads that are meant for long reach, then you need the ES; for short reach, it would be the HS. You don't want the iridium plugs and you want a plug with little to no internal resistance.

Here's info on NGK plugs:

http://matchlessclueless.com/mechanical/ignition/spark-plugs/

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

R26
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NorCal
Joined: 10/13/2012
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Good to know

Just had a look on mine and I also have the short reach plugs. It makes sense to use the longer ones although as long as there isn't any interference.

Grant R26
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VBMWMO #8145
Toronto Canada and Long Island, Nova Scotia
Joined: 03/28/2011
Posts: 158
Thanks Kurt and thanks R26 I

Thanks Kurt and thanks R26
I spoke with Vech today and he tells me that long reach is wrong. they will work but with time as you get carbon build up you will have flakes of carbon peel off them as you thread them out. So they are coming out and will be tossed.

so short reach it is.

The “short reach” NGK B8HS with half inch of thread are the correct plugs for both my R51 and my R27

cheers
Grant in Toronto

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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So what was the issue with

So what was the issue with the original short reach plugs. You said you put in the "wrong" long reach plugs and the bike began to perform well. Was it just that the short reach plugs failed?

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

R26
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The plot thickens.....

Sounded good although to replace the short plugs with the long ones and voila !!! bike runs like a top Smile I still ordered a set just for kicks ....

Grant R26
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VBMWMO #8145
Toronto Canada and Long Island, Nova Scotia
Joined: 03/28/2011
Posts: 158
I rode the bike to work the

I rode the bike to work the last three days on the long reach plugs until the correct ones came in today...apparently a few hours use is not a problem but one does not want the threads to get heavily carbon'ed up or your bore could get scored when you take them out.

the problem was not the long or short reach...my plugs must have been toast...simple as that

Grant
in Toronto

Grant R26
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VBMWMO #8145
Toronto Canada and Long Island, Nova Scotia
Joined: 03/28/2011
Posts: 158
Hi Kurt the original short

Hi Kurt
the original short reach plugs were a little carbon'ed up but not enough to worry me...but while playing with timing, carbs etc and kicking the bike over several hundred times ( felt like that anyway...grin) I oiled them up more. did de-grease and clean them and assumed they were not the problem...but could not get the left cylinder to run

Next time I'll make the spark plugs the first thing I do !! They are cheap and take a minute to put in so why not. That said, I get thousands of miles out of plug on my R27 but I never get it oiled up in the first place

I did note a rather dodgy connection at the spark plug cap and corrected that which may have been the original cause of the tendency to misfire on the left cylinder....especially in the rain.

All is well in that department now.

Keep up the great work Kurt. Don't know what I would do without this blog and my Barrington Motor works manual !!

Grant

R26
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NorCal
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Good to hear !

Bike is running fine ...that's a relief for sure.

Kurt is always there with great input Smile

Grant R26
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VBMWMO #8145
Toronto Canada and Long Island, Nova Scotia
Joined: 03/28/2011
Posts: 158
Happy ending to my timing and spark plug issues

Hi Kurt
Just a followup on my spark plug issues; Clearly it was never the spark plugs; they were simply a symptom of too advanced timing.

things went downhill about 1 week later. About 80 km from home it started missing again. Running on the right cylinder...could pull off the left spark plug lead at 50 mph and made no difference. Managed to make it down Digby neck (Nova Scotia) ...about 30 miles plus catch a ferry back on to our home island and another 10 miles home. Whew ! the sweet spot in the "power curve" was about 90 km/hr and as long as nobody pulled out in front of me I was fine. my R51 had turned into a R26 (grin)

figured it had to be timing. Rigged up my buzzer across the points and roughly calculated that it was 20 to 25 degrees BTDC !!!
This is a thumbnail guess based on the window's width of 8 degrees according to Barrington

I'm guessing the guy who put in the new advance governor for me last year figured the timing was close enough as the bike ran...fiddled with the carbs and handed it back to me running. Simply amazing how forgiving these low compression engines are considering how far off it was. The points must have just worn enough to advance it another degree and the tipping point was reached and everything went off the rails

The points plate took a lot of shifting to get it back to 9 degrees BTDC. Good Grief !

Started first kick and now runs amazingly well. Did a 500 km run yesterday and the bike has noticeably more power, sounds better, smoother and top speed is higher. I realize that I have to revisit ththe timing as no doubt I have a couple of degrees of differential timing to sort out but I'm just enjoying the bike so much now.

I had no idea what I was missing! My R51 seemed fine to me compared to my funky old Norton single. Duhhh

Next time I won't hesitate to dig into the timing. I must admit that looking at the R51 magneto gives me shivers compared to the one screw set of points on my Norton magneto (manual advance) but the Barrington manual made it all possible.

Grant in Toronto

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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Holy cow! That's really

Holy cow! That's really advanced and no wonder no power. Probably the low compression engine saved itself...do that to an R69S and likely you'd end up damaging a piston. Smiles ahead I'm sure!!

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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