Author Topic: Glow plug selection  (Read 808 times)

Offline Mike R

  • Full Member
  • ****
  • Posts: 160
  • Ottawa, ON
Glow plug selection
« on: February 20, 2023, 12:44:41 AM »
Looking for some advice.


I need to acquire 9 glow plugs for the engine I'm building (P&W Wasp Jr. 1/6th scale, 22mm bore x 24mm stroke), and as I'm nearing the cylinder head machining stage I thought it would be good to have them in hand for trial fitting.


The drawing set I have does not specify the plugs other than the thread (1/4"-32).


My question is - can I expect to buy for ~ $60 a set of generic "N3" plugs ("hot" - for lower nitro content in fuel - nominally designed for an RC car engine these days) and expect to have reasonable success?  Are these cheap plugs "good enough" or do I need to go for name brands (i.e. OS,
To be clear success to me is an engine that idles and runs up to a reasonable speed - this engine will never power anything so easy starting and running are the goals.


i.e. something like these: https://www.amazon.ca/NICELEC-Stainless-Steel-Silver-HSP1/dp/B091DQPBK7/ref=sr_1_7?crid=1UQW2UN0H9ID4&keywords=N3+glow+plug&qid=1676851726&sprefix=n3+glow+plug%2Caps%2C88&sr=8-7#customerReviews

Offline petertha

  • Full Member
  • ****
  • Posts: 782
Re: Glow plug selection
« Reply #1 on: February 20, 2023, 01:38:31 AM »
The general recommendation goes: 4S fires half as frequently as 2S so heavier/specific wire element is required to hold heat longer. And particularly at idle & transition where the bench runners operate. I've decided to install OS-F plugs on my 5-cyl radial because that plug is always what is recommended on their own 4S engines, single or multi cylinder. They are spendy & getting rarer these days, but RC Japan was awesome. Best prices compared to anywhere in N-Am, fast shipping. They also have other flavors of 4S plugs, Enya & YS, maybe others. Note that 4S plugs are a bit longer than regular plugs so good you are checking now. I have also read where 2S plugs were run on 4S & done so myself, but now its more about specific details: what kind of 2S plug, heavy element, compression ratio, nitro%, predominant rpm range... etc. I intend to test both when the day comes but the cost difference may not be enough to fret about. Good luck!

https://www.rcjapan.net/index.php?main_page=advanced_search_result&search_in_description=1&keyword=glow%20plug&inc_subcat=0&disp_order=1&page=2&zenid=at78kb0eethmbhr3mbmc4pes43

Offline Mike R

  • Full Member
  • ****
  • Posts: 160
  • Ottawa, ON
Re: Glow plug selection
« Reply #2 on: February 20, 2023, 03:00:41 AM »
Thanks for the advise and link to rcjapan, although you may have given me a new dilemma!  I was steering away from the spark ignition variant, in part due to issues finding spark plugs for engines this small, but stumbled on them at that website and at a very reasonable price - only $1 more than the OS type F plugs.

I think I'll stick with glow - far less stuff to mess with and get right - this is a complicated / difficult build for me already and I'm reducing complexity where I can.



Back to the issue - how long a "reach" is an OS type F from its sealing face to the end of the body in the combustion chamber?
The engine drawing shows 4.8mm for the plug, any more and I need to start considering notching the piston or some other creative solution.


Offline petertha

  • Full Member
  • ****
  • Posts: 782
Re: Glow plug selection
« Reply #3 on: February 20, 2023, 05:28:25 AM »
Here you go. They are caliper measurements of OS-F but hopefully within a couple thou. Under the surface indicated by zero is the copper washer which measures .027" thickness.

Also note the stem where the glow plug clip engages of OS-F is slightly larger diameter than 2-S plugs. Reason I mention is this may be of interest - I found some nice wire/clip assemblies from AliExpress used for remote RC wiring & you need to specify which plug type. They have kind of a spring retainer/conductor. I've tested under voltage & seems to light up well. Seems like it will be sufficiently secure.

Offline petertha

  • Full Member
  • ****
  • Posts: 782
Re: Glow plug selection
« Reply #4 on: February 20, 2023, 05:42:20 AM »
I spoke to these guys a while back. Its too late for my radial, I'm committed to glow on multiple fronts. But FWIW you can get spark plugs in the same 1/4-32 TPI thread size, but they are taller as shown on sketch in link. I'm not sure if these are the Paul Knapp ?sp? plugs but they seem to get great reviews (35 USD/plug). The other expense is ignition module. He offers a 5-cyl box for 285 USD. I asked about larger cylinder count & he said no problem, tell me what you need. The good part is all you require aside from carburation & a few other gasoline specific considerations is a magnet pickup on the prop hub & the brain does the rest for timing. Seems to have a reputable track record in RC. There are some YouTube videos. My next engine is to intentionally to explore this (gasoline/spark) aspect, probably a 2-cyl opposed.

https://ch-ignitions.com/product/rimfire-vr2-spark-plug-made-in-the-usa/

https://ch-ignitions.com/product-category/ignitions/5-cylinders-cdi/

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9463
  • Surrey, UK
Re: Glow plug selection
« Reply #5 on: February 20, 2023, 07:06:30 AM »
The length of the 10-40 plugs shown on the drawings is shown on Rimfire's website which you may want to compare with the length of alternatives. Also look at Steve Huck's plugs

https://sparkplugs.morrisonandmarvin.com/

Offline Mike R

  • Full Member
  • ****
  • Posts: 160
  • Ottawa, ON
Re: Glow plug selection
« Reply #6 on: February 20, 2023, 04:55:48 PM »
Thanks for the details and sources Peter and Jason. 

Hahaha  what a rabbit hole I've gone done.  In my wanderings on ch-ignitions I saw that they have a 9 cylinder radial from UMS engines!  And considering that it comes with plugs, ignition and a carburetor all for an engine similar in displacement to the one I'm building, I'm slightly tempted to buy that simply because I get a 9 cylinder engine assembly to play with as an expensive fidget spinner!  Unfortunately not being made of money that is out of the question but a fun thought.

https://ch-ignitions.com/product/ums-9-115cc-gas-9-cylinder-radial-4-stroke-engine/


I'll stick with glow for now, and order the OS Type F plugs, and explore spark later on (maybe once I get to the next set of radial castings waiting for me!)


Offline jcge

  • Full Member
  • ****
  • Posts: 87
Re: Glow plug selection
« Reply #7 on: February 20, 2023, 09:35:24 PM »
I found some nice wire/clip assemblies from AliExpress used for remote RC wiring & you need to specify which plug type. They have kind of a spring retainer/conductor. I've tested under voltage & seems to light up well. Seems like it will be sufficiently secure.

petertha - would you mind posting or sharing a link or further info on these connectors?
Thanks and regards
John

Offline petertha

  • Full Member
  • ****
  • Posts: 782
Re: Glow plug selection
« Reply #8 on: February 20, 2023, 10:18:06 PM »
Plug connectors I purchased from here. As mentioned, you need to specify the plug type. Regular plugs (typically 2-stroke) have slightly smaller diameter stems than 4-stroke plugs. I have seen some exceptions to this where some 2S also have the thicker stems, but they are rarer. Here is what's in the business end. A brass fitting that captures the retention spring, which grips the stem. Also you can kind of bend the wire at right angle if that suits as long as you don't crack the solder. I tested one & they can easily be unsoldered to put into this position.

https://www.aliexpress.com/item/10000078404976.html


Offline jcge

  • Full Member
  • ****
  • Posts: 87
Re: Glow plug selection
« Reply #9 on: February 21, 2023, 12:37:42 AM »
Clever method - coil spring inside - thank you.
Regards
John

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal