I’ve always tightened spark plugs by feel and never had a problem but decided to use a torque wrench when fitting new plugs to my 900ss earlier today, evidently 177 lbin is correct but blimey that seems tight!, took mine to 150 lbin and it’ll have to do, what do you tighten yours to?
Just checked torque setting for my 748 and the Haynes manual says 20nm. When converted is the same at 177 lb in Steve
Yes that’s 177 lbin, my NM torque wrench does go that low but it’s a big wrench wheras my lbin wrench is a bit more delicate.
Yes, give them a check, 150 lbin feels like more than enough to me, that said Ducati and the plug manufacturers know their game, maybe I’ve been under tightening for the last 40 years!
I figure the one place you don't want to strip threads is there, especially wihh a relatively soft material like they use now. Feel for me.
Important to tighten according to spec especially if working on someone else's bike. Without torquing to spec you can't always count on the gasket being properly squished. Under torqued may allow blow by. Over torque there could be an issue with distance from electrode to piston(should also check the gap is correct too). Bottom line, might as well torque and gap to spec to reduce unknown variables if performance is questionable.
as a side note...I always keep a couple of used known working spark plugs around. I've replaced plugs and had them not work or stop working shortly after. Nice to have a good one on hand to troubleshoot with.
Yes Matt, I had it checked a couple of months ago, I think what I’m saying is that 20nm feels a lot in comparison to what I’ve always regarded as the correct “feel” which is hard to describe of course but what I’ve always done is tighten the plug down until I feel the washer crush, then feel the plug stop as though it’s “bottomed” then give it maybe a further quarter turn, after doing this yesterday I applied the torque wrench and got about another eighth of a turn to achieve 150 lbin, at this point it felt very tight, if I had to guess I’d say it was around 130 lbin before using the torque wrench, now if I was reassembling an engine I’d follow the torque figures to the book without question but with plugs I appear to be a bit over cautious! , that said I’ve never had a plug come loose so most likely I’ll be a bit arrogant here, ignore the manufacturer and continue to do it my way
Hi Faith, I can’t argue with your points above, other than when using my “feel” method there’s no way the plug would be loose enough to allow blow by, as I said 40 years without an issue, but your point holds that as a rule we should stay with the manufacturers recommendations, maybe I need to be a bit braver! (another one that bothers me is 145nm on my Scrambler rear axle, that’s bloody tight!, I use that figure but in comparison to my 900ss 80nm it seems huge, at a recent tyre change the mechanic questioned my telling him it was 145, but that’s what it is).
I can't say that I've ever had a plug come loose, if anything they were hard to get out (back in the day, before I owned torque wrenches). People can do what they want, my point was that spark plugs are not just fasteners and torquing to the right spec satisfies other requirements. The washer is actually a seal, stuff can't get in nor get out. Even the threads can have a purpose beyond keeping the plug in place. Regarding the discrepancy in torque values between your bikes. Hopefully the mechanic would educate himself on why it is what it is and get back to you if something has changed. I would consider the size of the axle and grade of the hardware...and the application. Each bike has it's own specialty use and therefore different requirements.
