Tecumseh OHSK110 Plug RL86C or RN4C

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  #1  
Old 10-19-09, 06:47 PM
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Tecumseh OHSK110 Plug RL86C or RN4C

On my Ariens 1124 Pro snowblower is a Tecumseh Snow King Engine OHSK110 spec number 22173SD. Tecumseh specifies two spark plugs depending on the engine spec number. The manual calls for a RL86C [a hot short plug] for spec number below 223000 or RN4C [a cold long plug] for all other spec numbers. My 2003 OHSK110 [aka OH318SA] with spec number 221735 is below 223000.

The Tecumseh BSI manual (Basic Troubleshooting and Service Information) states on page 5 [pdf page 8] "Using an incorrect spark plug can cause severe engine damage or poor performance.

I have talked to two local Tecumseh authorized dealers and the Ariens technical support contact at 920-756-2141. They have all told me to use the cooler RN4C plug. One even stating that using the hotter plug could burn through the piston. I'm pretty sure the performance on this engine is not as good as it should be, it has been running the RN4C plug.

Who's right? The Tecumseh manual or the Tecumseh experts? If you believe I should use the RN4C, convince me I will not suffer poor performance. If you're certain I should use the RL86C, how are you so sure I will not "cause severe engine damage"? If you're not certain, please refrain.
 
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  #2  
Old 10-20-09, 06:18 AM
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The Hot and Cold plug gets a lot of discussion with an equal amount of confusion.

The statement concerning incorrect plug is aimed at length of the threaded portion of the plug.

Your engine should use a RL86C spark plug.

Tecumseh published several Quick Reference booklets that are worded differently.

OHSK 110, 120, 130 models with specification nos. below 223000 use RL86C

http://smallenginediscount.homestead...rvice_Info.pdf

See Step 3: Heat Range Selection, “normally a hot spark plug is used in a cold engine (low horsepower)”

Champion Spark Plugs for Proven Performance
 
  #3  
Old 10-20-09, 11:53 AM
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Originally Posted by Airman View Post
...
Your engine should use a RL86C spark plug.
...
Given this, Has anyone else run these two plugs in a similar machine and can you report on the differences. That is, does the correct RL86C allow the engine to run more smoothly? Have you noticed any other differences?
 
  #4  
Old 10-20-09, 01:44 PM
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Originally Posted by vicfixit View Post
Given this, Has anyone else run these two plugs in a similar machine and can you report on the differences. That is, does the correct RL86C allow the engine to run more smoothly? Have you noticed any other differences?
I am surprised you have not damaged your engine running the RN4C spark plug. The RN4C spark plug is 0.250 (¼) inch longer than the RL86C spark plug.

RL86C has a 0.500 (½) inch reach.

RN4C has a 0.750 (3/4) inch reach.

If your engine were under warranty, Tecumseh would not warrant damage incurred by using the RN4C spark plug.
 
  #5  
Old 10-20-09, 04:45 PM
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Originally Posted by Airman View Post
I am surprised you have not damaged your engine running the RN4C spark plug. The RN4C spark plug is 0.250 (¼) inch longer than the RL86C spark plug.
I purchased this 1124 Pro used to replace a safety challenged 1974 ST624 and have yet to use the 1124. As I get it ready for winter I noticed the plug mis-match. The machine was serviced for the prior owner at an Ariens dealer who presumably put in the RN4C plug. As mentioned in the original post, two local dealers and the Ariens own tech support tell me to use the RN4C. Thus the conundrum.

The "experts" score is four to two in favor of the RN4C vs RL86C, with Airman and myself in the minority. I'd just expect a better consensus from the so called experts. While I'm planning to use the RL86C, I'm interested in some real world user experiences.

As for the performance. The unit seems to run ok, and the plug itself is not damaged in the cylinder. Gap is right on at 0.030. The last quarter inch of thread and the plug insulator and gap are quite black. When running I expected better performance given my experience with the 1974 Ariens. Anyone else running the RL86C in a similar machine, I'd like to hear from you in regards to your local dealers' advice on the two plugs.
 
  #6  
Old 10-20-09, 06:35 PM
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RN4C or RL86C

The parts break down IPL shows RN4C I would believe the parts break down. You can down load a PDF here:

http://www.landscapepower.com/pdf/Te...10-221735D.pdf

You should right click and choose save as

Or view a break down here:

Parts and Diagrams for Tecumseh OHSK110-221735D

But the easy way to check which plug you need is to measure the thread depth in the head. If it is 3/4" RN4C 1/2" RL86C.

AJ
 
  #7  
Old 10-20-09, 07:35 PM
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I never noticed a conflict in Tecumseh documents before. That would make a mess of a warranty claim.

I use a Spark Plug Application Chart for all engines. I looked at a couple of Spark Plug Application Charts I had in the shop and they showed RL86C for the OHSK110 spec number 22173D.

I am with AJ-Allen, to know for sure measure the thread depth in the head.
 
  #8  
Old 10-20-09, 08:46 PM
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I have seen the document mentioned by aj-allen recently. It's not clear to me what the source of this document is. Is it an official Tecumseh document or something adapted from another document.

I agree that measurement of the thread depth is warranted. The carbon build up on the last 1/4" thread of the installed RN4C suggest to me it is not the correct plug.

If anyone has an email contact at Tecumseh who could vet this discrepancy that would be useful.
 
  #9  
Old 10-21-09, 06:35 AM
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I quit with Tecumseh several years ago and sold my microfiche. Tecumseh represented less than 10% of my work and doing business with them was more costly than what I was making.

My distributor now sells Tecumseh parts and provides dealers with all Tecumseh data. I looked at Tecumseh Parts Smart, online parts and data resource, shows the RN4C spark plug used on all engines except OHSK110-221001A, which lists the RL86C spark plug. They have the same cylinder head PN.

I would still measure the spark plug hole thread depth and use that as the basis for the plug to use.

There is a service bulletin 503 for rich running engine above 7000 feet. Are you in this situation?
 
  #10  
Old 10-21-09, 07:05 AM
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Originally Posted by Airman View Post
...shows the RN4C spark plug used on all engines except OHSK110-221001A, which lists the RL86C spark plug. They have the same cylinder head PN.
...
Presumably the 221001A and my 221735D have the same cylinder head from your description. I do plan to measure the threaded hole depth and then try the RL86C and do a comparison test to the RN4C. I just have to locate an RL86C locally.

Originally Posted by Airman View Post
...
There is a service bulletin 503 for rich running engine above 7000 feet. Are you in this situation?
I'm well below 1000 feet so the elevation shouldn't be a problem.

Thank you Airman for your insights and suggestions.
 
  #11  
Old 10-23-09, 01:54 PM
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The RL86C is the correct plug.

Originally Posted by vicfixit View Post
I do plan to measure the threaded hole depth and then try the RL86C and do a comparison test to the RN4C.
Measurements of the thread: 12 threads from cylinder to the plug seat (12 threads/24 tpi = 1/2" ).

I replaced the RN4C (3/4" thread) with the RL86C (1/2" thread) and the unit runs fine for the five minutes I ran it. Then I removed the plug and it was still quite clean with no build up. I plan to again inspect the plug after it has cleared at least one snow storm and see how it looks. The RN4C plug was quite carbon covered when it was removed.

Bottom line, check your engine spec number and count your threads if you're unsure before you accept an RN4C plug for your Tecumseh engine.

Again thank you to Ariman and aj-allen for their input.
 
  #12  
Old 01-04-10, 04:03 AM
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More about plugs - really confused now

I have an OHSK 110 Spec 221703A in a MTD (Yardman) snowblower. I bought it used; it has the RN4C plug. I measured the depth of the spark plug hole to be 3/4 inch, which seems right for the plug.

Everywhere on the web seems to say that I should be using the RL-86 plug because my spec is less than 223000, except for

Parts and Diagrams for Tecumseh OHSK110-221703A

The consensus seems to indicate the RL-86 plug because of the spec #, but the hole is 3/4" deep.

Can I use the RL-86 in the 3/4" depth?

I'm in Canada, if that matters.

Thanks in advance
 
  #13  
Old 01-04-10, 05:34 AM
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Originally Posted by ddewolfe View Post
I measured the depth of the spark plug hole to be 3/4 inch, which seems right for the plug.

Everywhere on the web seems to say that I should be using the RL-86 plug because my spec is less than 223000, ... but the hole is 3/4" deep.

Can I use the RL-86 in the 3/4" depth?
If you counted the threads to measure the depth and came up with 18 threads then no I wouldn't use the shorter plug. The ignition would be in the last 1/4" of the plug hole which may cause burning damage to the head.

If you used another method to measure your depth, I would recheck the depth by counting threads. I used a hook pick to count the threads and counted several times at different points on the hole to be sure.

Having replaced my RN4C with the RL-86 I have found the engine to run very well with little to no black smoke at startup. Good luck.
 
  #14  
Old 01-05-10, 07:40 AM
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Thread counts and plugs

Hmmmmm.... (aaarrrrgggghhhhh)

I counted the threads in the hole with a hook-pick and got 13 as an average for 4 measurements. I also get 13 on the RN4c Plug - washer to tip - , so the threaded portion of the RN-4C plug is the same length as the threaded length of the hole, and therefore seems to be the correct plug, in defiance to all the Tecumseh OHSK110 211703A information.

The length of my RN4C plug from the washer to the end of the barrel is 0.69", and to the end of the electrode 0.75".

My plug is not 24 threads/inch. It is 18 tpi.

So I guess it is the RN-4C plug. any comments from the experts?

--Dave
 
  #15  
Old 01-05-10, 12:39 PM
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Originally Posted by ddewolfe View Post
Hmmmmm.... (aaarrrrgggghhhhh)
My plug is not 24 threads/inch. It is 18 tpi.
I agree Hmmmmmmm & aaaarrrrgggghhhh.
I've gone back to my Ariens machine and looked at the threads again. I've also looked at plug specs again. From what I've read the plug thread diameter is 14 mm with a pitch of 1.25. Correct me if I'm wrong but this would give a thread per inch of:
25.4 mm/inch divided by 1.25 mm/thread =~20.3 threads per inch. Which is neither 18tpi nor 24 tpi.

I retract what I said about the shorter plug causing problems such as burning the head. This after reading Spark plug - Wikipedia, the free encyclopedia.

I have reconsidered my plug choice and even though the RL-86C seems to be performing well in my Ariens I have replaced it with the RN4C. The removed RL86C appears to be in very good shape and the head seems to have suffered no visible damage to the lower threads in the plug hole. After the next snowfall requiring the Ariens I'll report what I find.
 
  #16  
Old 01-06-10, 03:44 AM
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Plug pitch

You are right - the pitch is not 18 tpi, but 25.4 / 1.25 = 20.3 tpi. I got the 18 off a champion website - industrial plugs when I first started looking at this spark plug stuff..

I spoke to the previous owner of the machine yesterday - he never changed the plug, so it came with the RN4c.

For me, I'm going to stick with the RN4C plug as it fits the head perfectly.

Thanks for your comments, vicfixit.....
 
  #17  
Old 01-06-10, 04:45 AM
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In racing engines I would use different "heat" plugs to help control early detonation and plug fouling. There was no physical size difference between hot and cold plugs. The insulating ceramic around the electrode was a different shape on the different plugs. Yes, using the wrong "heat" plug could cause engine damage with pre-ignition but you have a pretty large safety margin with a stock small engine.
 
  #18  
Old 12-11-10, 01:08 PM
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Hello all, Hello Cheese,

I know, long time no post. Well Id like to bring this subject back up.

I own a Toro 1128 OXE model 38650 snowthrower with the Tecumseh 'Snow King' 11HP engine. The engine is a Tecumseh OHSK110/OH318SA with spec number 221812B. I purchased this snowthrower brand new in October 2005 and nobody has worked on it since except me. It currently has 32 hours on it. I was getting it ready for this winter season and changed the oil and checked the spark plug. The spark plug in it is the original spark plug and is Champion RN4C. The plug doesnt look too worn and the gap is OK but its a bit black/sooty so I was thinking of replacing it. I was curious and looking at the Tecumseh Operator's manual that came with the unit from Toro I was surprised that the manual does not give the part number for the replacement spark plug. On page 15 (section F) the manual mearly states that the plug should be checked annually, or every 100 hours and that the gap should be .030. There is a note that states (in italics) 'A resistor spark must be used for replacement. Contact your authorized Tecumseh Servicing Dealer for a Tecumseh spark plug'. Well thats fairly useless info. So I looked in the Toro Operator's manual and lo and behold on page 19 of that manual it states that the replacement spark plug is Champion RJ-19LM (in bold letters). Out of curiosity (again) I decided to go to the Champion Spark Plug website and see what the differences were between the RN4C that was in the engine and the RJ-19LM that the Toro manual said was the correct replacement. Well both plugs have a 14mm thread but the RN4C has a 19mm (3/4") reach and the RJ-19LM has 9.5mm (3/8") reach. Well something cannot be right here, thats a big difference, so...I went to the Tecumseh website and in the 'Basic Troubleshooting and Service Information Document' page 5 found that for a OHSK110/OH318SA engine with spec number below 223000 the plug is Champion RL86C, and for spec number above 223000 the plug is Champion RN4C. My engine is spec number 221812B so according to that document it should use the RL86C. Another check of the Champion website shows this plug to also have a 14mm thread but with 12.7mm (1/2") reach.

Talk about a 100 percent FUBAR'd set of contradicting specs! Three different spark plugs with three different reaches!!

Now I have no idea what is the 'correct' plug for this engine and I dont think Toro or Tecumseh do either. I suppose the best thing to do is stay with the RN4C plug that the engine came with. Its the longest reach of the three plugs and it has not done any damage in the 5 years Ive run the machine. That would be my greatest concern - that whatever plug I use caused no mechanical damage to the engine.

Im wondering what you all make of this. ?????

Thanks,
Paul
 
  #19  
Old 12-11-10, 02:25 PM
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Paul the Toro Manual is showing the plug for the "L" head engine not the "OHV" engine. I don't know how the 'Basic Troubleshooting and Service Information Document' Got so wrong but RN4C Tecumseh number 34645 is the corrrect plug.

AJ
 
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