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Old 11-17-2013, 02:58 PM   #1
JonnyCash OP
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Plug readings…. on a Guzzi

Hi folks, I pulled out my plugs today, and here's what they looked like.

[IMG]IMG_2468[/IMG]

The bike is a T3 with an 89mm top end, small carbs, small valve heads, jetted rich, I know. I've never seen such red, rusty looking plugs before. Anyone know what that indicates? I'll add that the bike pings, and I deal with it by running octane booster, but still it pings. They are high, flat dome pistons, making a high, but not known CR. I'm going to deal with that this winter, but just thought I'd run these plugs by you all to see what you think. Thanks.
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Old 11-17-2013, 03:36 PM   #2
k-moe
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The red you are seeing is caused by deposits from the octane booster. What octane fuel are you running (pre booster)?
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Old 11-17-2013, 03:48 PM   #3
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91 is the best I can get around here, so that's what I run. I've been running half a bottle of Lucas booster per tank, about 6 gallons. I hadn't even thought that it could be the booster, I'm glad I asked. Thanks!
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Old 11-17-2013, 04:39 PM   #4
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Originally Posted by k-moe View Post
The red you are seeing is caused by deposits from the octane booster. What octane fuel are you running (pre booster)?
nice job k-moe,nailed it in 30 minutes
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Old 11-17-2013, 05:39 PM   #5
cam14
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I'm not an expert, but to help lessen pinging, think running a colder rating on the plug will help and if you can get a plug with less protrusion (shorted threaded part) in to the cylinder head will lower the static compression a small amount. Also, running a longer duration cam will lower the dynamic compression if that is an option for you.

HTH
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Old 11-17-2013, 07:24 PM   #6
Kai Ju
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My '94 R100GS pinged like crazy, even on premium fuel. The expedient answer was to down shift and bring the revs up.
Ultimately I tightened the squish band from 0.150" to just under 0.050", which also raised the compression since it was achieved by milling the head. After doing that it stopped pinging, even on the occasional tank of regular fuel.
You said you would address the pinging this winter, make sure to measure your squish.
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Old 11-17-2013, 07:26 PM   #7
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Retard the advance a few degrees until you can fix it permanently.
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Old 11-17-2013, 07:53 PM   #8
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Retard the advance a few degrees until you can fix it permanently.
Agreed. Pre-detonation is an engine killer. You can get away with some, but only for so long.
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Old 11-18-2013, 04:33 AM   #9
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Thanks for the help, guys. I had a lengthy thread going about my pinging issues a while back. I backed off the timing so I could keep riding it. It still pings a little, but if I back it off any more the bike becomes very hard to start. I'm actually going to pull the top end off today, to see how it all looks. Riding season is all but over here now, and I still have the BMW in commission for the odd warm day.Hopefully I didn't harm anything, but I doubt I did. I'm fairly sympathetic to machinery. I will most likely end up milling off a little from the piston crowns, but I'm entertaining the idea of dual plugging the heads, which absolutely ended pinging problem on my high CR R100S.
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Old 11-18-2013, 04:41 AM   #10
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Originally Posted by Kai Ju View Post
My '94 R100GS pinged like crazy, even on premium fuel. The expedient answer was to down shift and bring the revs up.
Ultimately I tightened the squish band from 0.150" to just under 0.050", which also raised the compression since it was achieved by milling the head. After doing that it stopped pinging, even on the occasional tank of regular fuel.
You said you would address the pinging this winter, make sure to measure your squish.
Yes, that is something I'm going to look into! I've never played with that on a 4 stroke, but on my RD350 I played with it and got great results. I'm sure my squish band is quite wide currently, as when I put this engine together I put two base gaskets under the cylinders, knowing that my CR was likely going to be an issue. Perhaps my trying to help only hurt. So you're saying that your bike stopped pinging after milling the heads to close up the squish? Did you take any material off the piston crowns or out of the combustion chambers? When I did the RD, I milled the head gasket surface to close squish, but then took material out of the combustion chambers so as to keep chamber volume the same.
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Old 11-18-2013, 05:50 AM   #11
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Too much squish clearance will cause detonation in some cases. Closing up the squish will only work if the resulting volume does not raise compression enough to detonate. 'Tis a double edged sword.

Dual plugging hemispherical chambers is a good idea these days if you want performance and wish to run pump gas. Best case is adjust squish,chamber volume,dual plug w/adjustable ignition and some dyno time to sort the advance curve. In the end well worth the time,effort and cash involved.
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Old 11-18-2013, 07:03 AM   #12
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Pulled off the heads this morning here's what I found
[IMG]IMG_2470[/IMG]
[IMG]IMG_2469[/IMG]

I was happy to see that everything looked great, well to my eyes anyway. I put about 3000 miles on the bike since it was last apart. Lots of red deposit from the booster, but the only thing I can see resulting from the pinging is the flecks of deposit absent from the top of the piston dome, and from the exhaust valve. The exposed metal in those places doesn't look etched or eroded to me, so I guess I'll consider myself adequately kind on the throttle. I measured the squish at .127", which seems a bit wide, but I don't know what people shoot for on Guzzis. I know on my RD350, I had it at .035", but this is a different beast. I also measured the height of the piston crown at .300" above the squish band, and then I measured a stock 850 T3 piston I have laying around at .180" which makes what 3mm difference? That's a lot I guess. I've been eager to pull it apart, but until the weather grew cold, I haven't been willing to do it. It was just too much fun to ride!
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Old 11-18-2013, 02:46 PM   #13
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Originally Posted by JonnyCash View Post
Perhaps my trying to help only hurt. So you're saying that your bike stopped pinging after milling the heads to close up the squish? Did you take any material off the piston crowns or out of the combustion chambers? When I did the RD, I milled the head gasket surface to close squish, but then took material out of the combustion chambers so as to keep chamber volume the same.

The only material I removed from the pistons was in the valve pockets to clear the bigger intake valves and to maintain a 0.040" clearance between the valve and the piston. So yes, that may have affected combustion chamber volume, but the big gain was made by reducing the squish band. The stock configuration wasn't really a squish as much as it was a place for unburned fuel and air to hang out.
I also did a 336 cam and 40 Bings and the end result was an increase of 18 % in horsepower at the rear wheel.
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Old 11-18-2013, 02:54 PM   #14
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The cams you used likely had more overlap which tends to bleed off cylinder pressure at lower RPM reducing the likelihood of detonation.
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Old 11-18-2013, 04:12 PM   #15
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The cams you used likely had more overlap which tends to bleed off cylinder pressure at lower RPM reducing the likelihood of detonation.
Quite possible, but it doesn't negate the benefit of a proper squish band.
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