Yamato 80 rope plate and 18mm sparkplugs

[fbref5269]

hi all,

looking for a rope plate for a yamato 80 and 18mm plugs, ngk 10. anyone have these gathering dust?

frank
52-E

[ZUL8TR]

18mm plugs for that are rare. What about 14mm head then NGk 14mm plugs easy to get or use adapters with 18mm head and go 1 step colder than the stock 18mm plug. I have adapters on 18mm head and my stock plug is a NGK A9N. I use NGK B10EGV with the adapters.

For the rope plate?

[fbref5269]

i do have a line on a 14mm head and may go that way. the plugs are hard to find. i do have the adaptor and may try that the next race. did you have any issues with the adaptors?

frank

[Tunnelman801]

Frank, On your post, you said,you had a line on a 14mm head for a Yamato 80 engine, and if you do. I need one also. I have a new 18mm head and 18mm to 14mm plug adaptors, but I do not like the adaptors. Please post me if you can help me. Thanks!! Tunnelman--William

[ZUL8TR]

i do have a line on a 14mm head and may go that way. the plugs are hard to find. i do have the adaptor and may try that the next race. did you have any issues with the adaptors?

frank

See PM

[Matt Dagostino]

Gary U.S. Pond has 2 boxes of NGK 18mm plugs......$25 per plug. Also i hear Montoya now has some.

[ricmontoya]

New roper plate $174.46 206-283-4773 ricstr4@gmail.com,
don't have the new spark plugs yet, however they are more expensive than the ones Gary Pond has.

[ZUL8TR]

New roper plate $174.46 206-283-4773 ricstr4@gmail.com,
don't have the new spark plugs yet, however they are more expensive than the ones Gary Pond has.

For that cost are the 18mm preferred over than the 14mm plugs in the 14mm head? If so why?

[dwhitford]

For that cost are the 18mm preferred over than the 14mm plugs in the 14mm head? If so why?

I believe the millimeter numbers refer to thread DIAMETER, not the reach (length) of the threads. So you could not run the 18-mm plugs in your 14-mm head even should you want to. The bigger 18-mm plugs were the standard size in the 1930s and some 1940s outboard engines, such as the Johnson SRs & PRs, & the Evinrude 4-60s, and Speeditwin, Speedifour, and Big Four.

If you had a Yamato 18-mm head, you could, as ZUL8TR mentioned in an earlier post, screw in an 18-to-14 mm thread adapter to reduce the thread diameter for the smaller-diameter plugs. Doing this can be iffy because of possibly poorer heat transfer thru the thread interchange, perhaps why ZUL8TR recommennded a heat-range change should you go that route. -- dave

[ZUL8TR]

yes I was referring to diameter. The post was a bit confusing. I meant for that cost of the 18mm plugs over what 14mm plugs cost in a 14 mm thread head why would you want 18mm plugs and matching head. Do the 18mm plugs in an 18mm thread head perform better than the 14mm plugs in a 14mm thread head and why? As far as using the 18 x 14 mm adapters the colder heat range plug is needed for exactly the heat transfer reason you cite. Recommended to do that by Ric Montoya.

[PRO-MOTIONRACING]

NGK A-8 3.00ea Bike shops can order them. Run the jetting a little rich.

[fbref5269]

don't the cooler ngk plugs have a higher number than the hotter ones?

[runabout333]

On Ebay,, I saw the 18 x 14 reducers with spark plugs for sale.
Ebay motors,,,, boat parts,,,, yamato.

[PRO-MOTIONRACING]

don't the cooler ngk plugs have a higher number than the hotter ones?

#4 the hottest I have ever seen, for motors that idle only. #5 very hot, low rpm, some old cars. #7 performance four strokes, some two strokes, I would guess most fishing motors. #8 two strokes, racing four strokes, most dirt bikes used these in the 70s and many do today, good for all properly jetted two strokes in the bitter cold of winter. #10 cold cold plug motor must be ran wide open to keep from fouling, I would run #9 in Yamato in cold weather. #11 so cold it is rare, very hard to keep from fouling but, very unlikely to cause detonation.
All plugs create the same spark, the difference is the plugs ability to dissipate heat from the center electrode to the head. Think of it like holding a piece of wire with a pair of pliers and heating it with a torch trying to burn a coating off. A long piece, say two inches gets red hot and burns off clean, while a short piece say 1/4 inch, all the heat is absorbed by the pliers so it is hard to get it to burn off clean.
If the plug gets to hot it will glow red and will pre-ignite before the spark event causing engine damage. Extra fuel can help cool the plug but it will also make you slow.
As a rule "the moment before detonation is the moment of optimum performance"

[dwhitford]

#4 the hottest I have ever seen, for motors that idle only. #5 very hot, low rpm, some old cars. #7 performance four strokes, some two strokes, I would guess most fishing motors. #8 two strokes, racing four strokes, most dirt bikes used these in the 70s and many do today, good for all properly jetted two strokes in the bitter cold of winter. #10 cold cold plug motor must be ran wide open to keep from fouling, I would run #9 in Yamato in cold weather. #11 so cold it is rare, very hard to keep from fouling but, very unlikely to cause detonation.
"

This is an excellent info summary.

I infer that present-day alky racers are using 11s because both Mike Schmidt & Chick LaRose recommended that I use them in my recently restored 250cc Quincy Z-engine. Chick also mentioned that I could probably substitute 10s OK in really chilly weather.

After more than 2 hours of Internet search, I finally fould some 11s at NGK Wholesale in California for $5.20 apiece, free shipping on orders of $50 or more. Mike said that was a good price nowadays.

These new NGKs replace the no-longer-available (?) gold-palladium Champions that I used to run and get free from the Champion rep at Valleyfield.

[Matt Dagostino]

don't the cooler ngk plugs have a higher number than the hotter ones?

Yes..........that is correct Frank. I run the 18mm head on my Yamato 80's. I have a set of NGK 18mm 9's that are a collectors item basically as NGK has not made them in many years. The NGK 10's are a little cooler and are prone to 'fouling' in the cooler temps!! I bump my timing up slightly to help with this issue and try not to 'idle' around to much while milling to avoid fouling a plug!