Tecumseh Valve Clearance & Spark Plug

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  #1  
Old 02-18-07, 05:29 AM
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Tecumseh Valve Clearance & Spark Plug

I have a Tecumseh Snow King engine. The model number is OHSK120 222012D. Can someone tell me the correct valve clearance and the crankshaft position at which those clearances are set? I have a Tecumseh mechanics handbook but it doesn't cover that particular engine. Also, what spark plug do you recommend for this engine? The owners manual calls for a Champion L-86C or equivalent. The previous owner had installed an NGK BR6HS. A local small engine service place recommended BPR5ES but I notice the reach of that plug is longer than the BR6HS. Should I be concerned about piston-to-plug clearance?
 
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Old 02-18-07, 07:59 AM
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I pretty well always use Champion RCJ6 in any 4 cycle small engine. Gapped at .030". This is subject to correction as to the specs but I've never had any trouble with these. I would suggest never trusting a spark plug out of the box. Seldom is it gapped to the required spec. This is up to the technician to adjust according to requirements.

I can not comment on valve clearance without the repair manual but in my esperience it is a pretty rare issue unless installing new valves which are usually a little over long and require grinding down the end of the stem to obtain spec and account for any cam wear.
 
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Old 02-18-07, 07:43 PM
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The RCJ6 plug is way too short, and won't go halfway through the spark plug hole. This engine needs a RL86C spark plug.

The valves on this engine need periodic attention because it is an overhead valve engine. Adjustment is required occasionally to maintain proper clearance and engine operation. The clearance between the valve and rocker arm should be .004" on both valves.
 
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Old 02-19-07, 04:44 AM
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At TDC?

Thanks for the plug and valve clearance information. Is the valve clearance measured at top dead center for this Tecumseh OHSK120 engine?
 
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Old 02-19-07, 06:39 AM
Azis
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Yes.
TDC is when both valves should be seated and positive clearance between the valve and tappet/rocker arm is required.
Spark plug "Reach" is generally the threaded portion of the plug, from the seat to the tip.
Heat range is determined by the amount of electrode that extends beyond the ceramic insulator and does not affect reach of the plug.
 
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Old 02-19-07, 08:17 PM
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Correct.

Azis, not sure what you mean with the info about the heat range and reach, but you are right that they don't have anything to do with each other. The reach on the RCJ6 plug is not nearly long enough for this engine though...it's an ohv, and takes a long-reach plug (according to the info I have). I don't remember the exact length though. I think the RCJ6 is around 3/4" and the RL86C is closer to 1 1/4"...roughly.
 
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Old 02-20-07, 02:56 AM
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As far as the position the piston needs to be in, it is important that the piston is positioned 1/4" downstroke past TDC on the power stroke. This ensures that the compression release mechanism (MCR) of the camshaft does not affect your clearances. The MCR will be active at low rpms (and none as is the case of setting clearances) on the compression stroke (which occurs on the stroke prior to the power stroke).
 
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Old 02-20-07, 06:05 AM
Azis
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Originally Posted by cheese View Post
Correct.

Azis, not sure what you mean with the info about the heat range and reach, but you are right that they don't have anything to do with each other. The reach on the RCJ6 plug is not nearly long enough for this engine though...it's an ohv, and takes a long-reach plug (according to the info I have). I don't remember the exact length though. I think the RCJ6 is around 3/4" and the RL86C is closer to 1 1/4"...roughly.
You stated one type as being too short, which refers to the reach of the plug IE: the distance the plug extends into the combustion chamber. A plug with the same/proper reach can have a different heat range and still be a correct application. Heat range is changed by the distance that the electrode extends beyond the ceramic insulator on the tip of the plug. More electrode showing= hotter spark.
A good example of what I mean is my KDX 2 stroke dirt bike. If I am just puttin around the back 40 roustin coyotes, I might use a hotter plug NGK B9ES which has a higher heat range(to help against fouling) than a B10ES which I may use when pounding the trails.
I thought it worth mentioning here especially since I have had people selling me plugs that had this info confused. As well as some other people may not be aware that one plug type will NOT work in all applications.
Reach is important as it needs to extend into the cylinder far enough properly combust the fuel/air, with out being too far to cause damage by moving parts.

Not to mention of the nearly 1300 questions on the A&P test, thats one of about 3 I remember
 
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Old 02-21-07, 06:05 AM
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Piston Position Clarification

Puey,

Knowing that a 4 stroke engine requires two complete crankshaft revolutions to complete one cycle, what is the easiset way for me to ensure I have the piston 1/4" on the downstroke of the power stroke? I assume I can use a pencil or dowel pin inserted into the spark plug hole to gauge the 1/4". How do I ensure I'm doing this on the power stroke? Do you agree that for this Tecumseh OHSK120 the correct clearances are .004" for both intake and exhaust? When I checked them at TDC (not certain which stroke I was on) they were intake = .004" and exhaust = .008"

As an aside, how does one determine that a particular engine has a mechanical compression release? Is it certain this engine does?
 
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Old 02-21-07, 06:54 AM
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With the piston at TDC it must be between the exhaust and intake stroke or between compresion and power stroke. TDC between exhaust and intake both valves are likely open and no clearance should be measured. TDC between compresion and power stroke is the only time both valves should be closed.
You can plug the spark plug hole with your finger and rotate the engine, as the piston comes up on compression you will feel air try to push your finger out of the hole.
The clearances you mention checking sound like they are on to me, the exhaust usually has slightly more clearance than the intake. I don't have reference for your exact engine however this Tecumseh manual http://www.cpdonline.com/692509.pdf shows valve clearance for all models it covers to match what you have (.004 .008). It also covers more on the different types of "Compression Release" used. MCR, BCR, RCR
 
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Old 02-22-07, 07:01 PM
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You need to watch valve movement to ensure you are on the power stroke. The power stroke immediately follows the compression stroke and is immediately before the exhaust stroke. Since you have an OHV engine, it is much easier to watch than it is on a flat head engine. With the rocker cover off (as I'm sure you're already there) rotate the crankshaft clockwise (as viewed from the flywheel end) and, yes, use a long wooden dowel in the spark plug hole to determine piston position and watch for the intake valve to open. On the next stroke (which will be an upstroke), you will take the piston to top dead center (TDC) and then continue in the same rotational direction 1/4 inch (of your dowel movement) past TDC. You are now at the position to set both valve clearances. Yes, this engine does have a MCR and therefore is important to follow my directions. Yes, .004" is correct for both valves. In order to determine if your MCR is functional, you must first set the clearances and then again rotate the engine CW and watch the valve closest to the PTO (power take off) end of the crankshaft for movement at just before TDC on the compression stroke. Mind you, it will be brief in duration and minimal in lift. Hope this helps and let us know in the thread how everything goes.
 
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Old 03-07-07, 03:26 PM
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Biker Bill Tecumseh Specs.

Hi Bill, Tecumseh Snow King OHSK120................Champion Plug # RN4C..Gap .030..........Value clearance should be set at TDC on comp. stroke, look an see, both values must be close... clearance should bo .004-.010, on both intake, and exhaust values..........Good Luck......Paul
 
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Old 03-19-07, 04:38 AM
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Problem Solved!

I installed the owner's manual recommended spark plug, a Champion L-86C. I adjusted the valve clearance as per Puey's instructions. Only one of the valves needed any adjusting and it was off by only a few thousandth's of an inch. Most significantly, I think, I soaked the carburetor in laquer thinner for 20 minutes and then rebuilt it using the Tecusmeh kit. We recently had 10 inches of snow followed by a signficant amount of freezing rain and rain which created some really heavy snow/slush. The engine ran without any backfire problems. Prior to the work outlined above, under these snow conditions the engine would have backfired and stalled repeatedly. Thanks to all for your help.
 
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Old 03-19-07, 09:17 PM
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Glad you got it fixed, and thanks for the update!
 
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Old 05-01-09, 12:23 PM
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Tecumpseh ORVM40 oil pump

I reassembling an Tecumseh ORVM40, I need to know if the oil pump needs to have the beveled side toward the gear or away from the gear.
 
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