Perlova Posted October 20, 2007 Share Posted October 20, 2007 I just changed the plugs on my R1100RT with new Autolite 3923 plugs. The old plugs were also 3923. However, the tip of the old ones had a beveled shape (see photo) which is different from the new ones (just squared off) . Is the old one worn that badly or has Autolite changed the style of their 3923 plugs? Link to comment
Stan Walker Posted October 20, 2007 Share Posted October 20, 2007 Normal wear for a plug that is left in the bike for lots of miles. I change my 3923 every 6000 mile service so I never see them that worn. Stan Link to comment
T__ Posted October 20, 2007 Share Posted October 20, 2007 I just changed the plugs on my R1100RT with new Autolite 3923 plugs. The old plugs were also 3923. However, the tip of the old ones had a beveled shape (see photo) which is different from the new ones (just squared off) . Is the old one worn that badly or has Autolite changed the style of their 3923 plugs? Perlova, Are you sure the old plugs were Autolite 3923? In the picture it looks more like the AP 3923 & those are platinum with the tapered center electrodes.. See if the removed plugs were AP 3923 & the new plugs are the cheaper just plain old 3923.. Twisty Link to comment
Perlova Posted October 20, 2007 Author Share Posted October 20, 2007 Perlova, Are you sure the old plugs were Autolite 3923? In the picture it looks more like the AP 3923 & those are platinum with the tapered center electrodes.. See if the removed plugs were AP 3923 & the new plugs are the cheaper just plain old 3923.. Twisty Yes, they are Platinum APP3923 that were in there. The new ones are just plain 3923 plugs.... That makes sense, it's a different plug.....I didn't think that they could wear so much as to be conical.... Link to comment
AndyT Posted October 21, 2007 Share Posted October 21, 2007 They didn't wear so much as to be connical. They (AP's) come that way from the factory and the standard regular 3923 are straight cut and flat. Two differently built plug! They both work great and if you change them every 6000 miles the cheaper regular 3923 should do just as well! Link to comment
redryder Posted October 21, 2007 Share Posted October 21, 2007 They didn't wear so much as to be connical. They (AP's) come that way from the factory and the standard regular 3923 are straight cut and flat. Two differently built plug! They both work great and if you change them every 6000 miles the cheaper regular 3923 should do just as well! Just on a lark, I decided to see how long a set of 3923s would last. They've been in there for 18,000 now and I just did a 66K service. They look great!!! Nice tan color, with no signs of abnoralities (other than the rider in the mirror). Just did a very good valve check (only 1 exhaust valve needed to be loosened about .001; all the others were spot on), a very precise TB, and the bike runs GREAT with no complaints whatsoever. At 67K it never run better. Yes, the test is still on, the old plugs are still in play. Just curious as to why we need to change the plugs every 6K when they'll last in our other vehicles for 100K. When it runs bad, I'll change the plugs. Link to comment
Stan Walker Posted October 21, 2007 Share Posted October 21, 2007 Just curious as to why we need to change the plugs every 6K when they'll last in our other vehicles for 100K Don't need too. But I usually pull them out every 6000 miles to allow me to inspect them as part of my service, plus it makes the engine easier to turn over when adjusting valves. At $1.30 per plug I just install new ones. That has the side benefit of giving me a new plug crush washer each time. Stan Link to comment
richrob Posted October 21, 2007 Share Posted October 21, 2007 Will the 3923's work in the 2003 RT as well? Link to comment
Perlova Posted October 21, 2007 Author Share Posted October 21, 2007 Just curious as to why we need to change the plugs every 6K when they'll last in our other vehicles for 100K Don't need too. But I usually pull them out every 6000 miles to allow me to inspect them as part of my service, plus it makes the engine easier to turn over when adjusting valves. At $1.30 per plug I just install new ones. That has the side benefit of giving me a new plug crush washer each time. Stan They are not $1.30 in Canada, more like $3.50. And our dollar is worth more now.....go figure? Link to comment
Jim Moore Posted October 21, 2007 Share Posted October 21, 2007 They work just fine on my '02 GS. Link to comment
Roger_R Posted October 21, 2007 Share Posted October 21, 2007 Will the 3923's work in the 2003 RT as well? ABSOUTLY..... .035 (inch) gap Link to comment
Perlova Posted October 22, 2007 Author Share Posted October 22, 2007 Well I just put the old plugs back in. There was a noticeable surge in my RT that was not there before. I took out the new plain jane 3923 plugs and put back the old APP3923 platinum tipped plugs. The surge went away or at least was very minimal with the APP plugs. What gives? Link to comment
NoHeat Posted October 22, 2007 Share Posted October 22, 2007 Well I just put the old plugs back in. There was a noticeable surge in my RT that was not there before. I took out the new plain jane 3923 plugs and put back the old APP3923 platinum tipped plugs. The surge went away or at least was very minimal with the APP plugs. What gives? Did you do a throttle-body sync after changing the plugs each time? Link to comment
T__ Posted October 22, 2007 Share Posted October 22, 2007 Well I just put the old plugs back in. There was a noticeable surge in my RT that was not there before. I took out the new plain jane 3923 plugs and put back the old APP3923 platinum tipped plugs. The surge went away or at least was very minimal with the APP plugs. What gives? Perlova, you do realize the base (as bought) electrode gap is larger on the APP 3923.. As a rule the larger the plug electrode gap (up to a practical limit) the better the idle & low speed performance.. The platinum itself has no real effect but both the electrode gap & the smaller center electrode could make a slight difference.. The direction the electrode gap faces inside the combustion chamber could also have a slight effect but personally I haven't shown that indexing the plugs on the BMW boxer make any difference.. Twisty Link to comment
Perlova Posted October 22, 2007 Author Share Posted October 22, 2007 [quote Did you do a throttle-body sync after changing the plugs each time? No ... no re-sync. But why would that have to be done? Link to comment
JamesW Posted October 22, 2007 Share Posted October 22, 2007 OK, I know that the primary Autolite plug is an AP3923 but what is the autolite secondary plug type number?? Is it also an AP3923? This would be for an '04RT twinspark. Called Autolite for help and they don't show any info on a secondary plug for the 04 oilheads. Link to comment
NoHeat Posted October 23, 2007 Share Posted October 23, 2007 [quote Did you do a throttle-body sync after changing the plugs each time? No ... no re-sync. But why would that have to be done? Because you were complaining of surge after changing plugs, and for sure surge is worsened if the throttle sync is off. Maybe I'm wrong, but I'm assuming that changing the plugs could cause the combustion to start just slightly differently when the plug fires, and this would affect the vacuum on the intake for that cylinder, and therefore the throttle sync. Hopefully a more knowledgeable motorhead will tell us whether that's right or wrong. Link to comment
T__ Posted October 23, 2007 Share Posted October 23, 2007 [quote Did you do a throttle-body sync after changing the plugs each time? No ... no re-sync. But why would that have to be done? Because you were complaining of surge after changing plugs, and for sure surge is worsened if the throttle sync is off. Maybe I'm wrong, but I'm assuming that changing the plugs could cause the combustion to start just slightly differently when the plug fires, and this would affect the vacuum on the intake for that cylinder, and therefore the throttle sync. Hopefully a more knowledgeable motorhead will tell us whether that's right or wrong. John, engine vacuum (actually negative pressure) really isn’t effected by when a spark plug fires.. Well unless the engine has a tuned headers & the engine is operating in the tuned RPM range.. The engine vacuum & TBI balance is controlled by the restriction in the intake (delta across the throttle plate),, that’s assuming that each cylinder is operating the same with the same compression, same cam timing, etc.. You should be able to completely short out a spark plug & not change the TBI balance or engine vacuum as long as the engine RPM stays constant.. Twisty Link to comment
HRminneapolis Posted October 23, 2007 Share Posted October 23, 2007 Q: why replace ordinary spark plugs (not platinum ones) instead of just resetting the gap? A: 20 years ago the answer was that the metal in the electrode ionizes after awhile and it takes higher voltage to jump the gap. Therefore periodically replace the plug and get fatter spark, and better gas mileage, for the same voltage. Link to comment
Paul Mihalka Posted October 23, 2007 Share Posted October 23, 2007 When I used the Autolite 3923 plugs in my R1100RT and my R1150R, I gapped them from new to 0.040" or 1mm. That and good engine tune took care of all the surging. Link to comment
AZgman Posted October 23, 2007 Share Posted October 23, 2007 Will the 3923's work in the 2003 RT as well? Yes they will! 10k miles on my set and they look brand new. Link to comment
Perlova Posted October 23, 2007 Author Share Posted October 23, 2007 When I used the Autolite 3923 plugs in my R1100RT and my R1150R, I gapped them from new to 0.040" or 1mm. That and good engine tune took care of all the surging. That is the gap that the existing platinum 3923 plugs were set to. They do seem to surge less then the standard 3923's with an 0.032 gap.... Link to comment
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