18mm spark plug reducer

[atoyot]

Oh, how I love a beating! Accordingly, check out this thought even though to perform this upgrade might be seen as sacrilege by some.

In order to use my compression tester, I'm going to have to find me one of these 18mm --> 14mm adaptors -



It's that or purchase a new tester for more money that I don't need to put out.

What occurs to me is that as long as I'm necking down to a 14mm plug thread with the attendant variety of spark plugs that fit that thread, why not keep the adapter in there and use a more modern plug with a reach that puts the firing points a lot closer to the combustion chamber (without the assistance of a lathe to turn down the 18mm plug as others have tried).

This is far, far from being a matter of concern. The original spark plug position's worked fine for over 50 years in these things. I'm just saying, as long as the tool is there, some experiments might as well be run.

Let's go, let's hear it. Get it out.

[rosbullterier]

My recently aquired Gunson compression tester contained both adaptors. It didn't cost all that much.

However, should you find where to obtain the 18mm reducer please tell me, I need one to match another head which already has one fitted.

[atoyot]

...should you find where to obtain the 18mm reducer please tell me....

OK, RBT, here are a few sources in your part of the world:

http://www.gsparkplug.com/products/acce ... ad_adaptor

http://www.vintagecarparts.co.uk/en/976 ... r-details/


It seems the larger markets for these (excepting compression testers) are piston aircraft, older marine or land vehicles, and some earlier model motorbikes (Harley Davidson, etc).

[rosbullterier]

Much obliged sir, I shall investigate.

[pistnbroke]

I note from the photographs that some of the adaptors are for 18mm taper seat plug holes so you may still need the lathe or enquire of the vendor .....

[atoyot]

Not a bad consideration. A tapered "plug" (the adapter) might seal well enough though it'll look a little off even if it doesn't leak.

I ended up with this http://www.tooltopia.com/innovative-of- ... -7885.aspx

[Collector Inspector]

UK,local to you?

http://www.gsparkplug.com/products/acce ... ad_adaptor

These are great!

Choose your heat range etc..................

Regards

B

[rosbullterier]

Are you saying, Collector, the Green Spark Company's adaptor is tapered?

[rosbullterier]

Incidentally atoyot, we had a lengthy discussion about using plugs with a different reach.
Pistbroke waxed lyrical at length how the spark should be nearer the gas.
I replied, well when will you chaps with lathes, engines, boats and rivers test your theories.

Nothing . . .

[atoyot]

Yes, I think I came across that thread. Lots of engineers in white coats with their slide rulers out, very few technicians getting dirty in the test laboratory.

My take on much of that was that the combustion chambers on these things aren't nearly so sophisticated so as to benefit much from the "perfect" ignition source placement. And, there doesn't seem to be a well documented problem with plugs fouling for lack of a gas stream blowing across the plug tip. Heck, I just picked up a Silver Century of unknown origins and filled it to the outer plug hole with oil, overnight. That, and the crankcase (carb is removed for deep cleaning) was filled up as well. This morning I dumped both, introduced a few cc's of fuel mix into the crancase direct, and the ba$t@rd started up and ran for a few seconds on the first pull. No, I don't think these Seagull engines have a hard time with ignition, recessed spark or not.

I went looking for an adapter because I don't want or need a new compression tester. I'll probably play with some spare plugs in stock though I'm not sure that a real difference will be found either way, other than on paper.



-ted

[Collector Inspector]

I am an engineer but have a "Grey Coat", basically because most of the time I am hands on yeh?

I still like having an edge with ignition gear, being electronic conversion under a flywheel, or, just a different plug at hand that does a slightly better job of it.....



Taper plugs suck by the way.....................

Regards

B

[atoyot]

Agreed..... I was never a fan of tapered plugs. It would be interesting to refit an electronic breakerless module under the hat rather than the points just for the sake of experimentation.

My adapter came in, and the compression readings on a 40+ and a Century+ are both about 2/3 of what I'd think they should show. That's 80psi and 40psi respectively, and yet both have very firm compression. One has to wonder if there's a material difference in the chamber volume with the adapter/meter vs. the spark plug in place.

With regard to the 40+, I even lapped a bit off of the head while replacing the copper gasket last week and it sounds just beautiful. It has to do with 320-grit wet&dry paper, penetrating oil, and a figure-8 motion. Possession of calipers is a bonus.

Anyway.... I've got an NGK BP5ES on the way and will, as soon as I'm allowed to play with boats again in a week or two, compare that with the adapter against the stock 18mm plug and file a report . And being as I've come across that Century Plus only in the last week or so, I'll need to try both.