stripped spark plug thread

[olcah]

Just managed to strip a plug on my 54 Erude 25 HP (even with a torque wrench on it for 20 ftlb d@mn). Should I look for another head or go with a thread insert? The motor is pushing fuel past the upper crank seal also. Even though I replaced the carbon seal and its internal oring so I plan to open the crankcase to replace the oring on the bearing. Will I have to remove the head to do or is replacement of the head separate?

[fleetwin]

I am the minority here, would recommend finding another head instead of helicoil/inserts, improper installation or compatibility could prevent the spark plug from dissipating heat properly and preignition.
I’m not sure I understand your second question, correct me if I misinterpret. But, you will need to remove the powerhead from the exhaust leg in order to split the crankcase and replace the oring around the upper bearing. Just seems like an oring failure is unlikely unless someone has had the powerhead apart and misassembled/forgot to install the oring.
Have you checked the crankshaft for sideways slop, perhaps the upper bearing is worn/rusted.

[dan-in-tn]

I don’t think the upper main bearing takes an o-ring in this application. I would make sure I put the quad ring in place of the o-ring inside the carbon seal. The part number evades me at the moment, but I am sure FrankR will be along soon to provide it. He can correct me if I am wrong about the upper main o-ring also. No you would not have to pull the cylinder head to pull the front half of the block for any other repairs you decide to make. I am with Don. I feel that an insert can be installed properly, but a cylinder head can probably be had for about the same price as a properly machined and installed insert. No heli-coils! Just my opinion.

Dan in TN

[olcah]

Fleetwin, If I change the head now would I have to disturb the head/head gasket later when I replace the print at the bearing? Looks like I would not have to per t2stroke . I replaced the upper carbon seal this winter with a new carbon and replaced the inner ring with the square type as recommended by Frank. After using it a few times I found fuel leaking in the seal area and running down on to the motor. So a couple of weeks ago I pulled the seal apart again and put in the factory recommended oring. I ran the motor (skipping) for a few minutes and oil was in the seal area with that also. Maybe the O ring around the bearing is bad.
I have an Rd15A with the same problem.

[seakaye12]

I faced the same situation when working on a Lightwin a while ago. Due to my not having experience with inserting helicoils plus not owning the insertion tools etc….I decided to replace the head. Of course; Lightwin heads are a dime a dozen….so it would of course depend on how successful you are in locating a suitable replacement. But; I would say…if you can find one at a reasonable price…replace it.

Sorry but I can’t help on the other aspects of your question.

Chuck

[johnyrude200]

Replacement heads are always preferable but not always convenient to find. Personally, I use the save-a-thread inserts over the helicoils for plug holes. The reason I do is that they are a bit more rugged in my opinion then helicoils.

I have observed that helicoils tend to allow cross-threading to happen again pretty easily. Also if they’re installed wrong (it’s kind of a finesse job to install them…only experience makes you good at it, and you generally get 1 try otherwise it’s ruined anyway), pieces can break off into the cylinder. I had this happen personally, where a piece of the helicoil broke off, stuck to the piston, and lit up like a christmas tree causing pre-ignition, and actually melted off the end of the piston (this all happened in about 15 seconds at WOT, which when you’re on the boat, by the time you look back and see a cloud of smoke and steam, it’s too late to do anything i.e. slow down/kill off the motor before seizing).

Helicoils also come unscrewed with the plugs, which just means if that person tries to reinstall the plug with the helicoil already on it, then everytime they do this and snug it down, they’re screwing up the soft aluminum more and more.

The save-a-thread inserts bore out the hole, screw into that same hole after being retapped, and then you take a hammer and installer tool (included in the package with the hole tap) to fold down a upper sleeve which locks it into place. No worries about getting stuck to the plug, or ever backing out. Plus by putting some thread sealer, it stops any leakage of oil/gas and seapage of compression on the power stroke.

Whatever you do, I would not recommend following the directions for installing either of these options by applying grease to the tap. Remove the head, install the insert/helicoil, clean it all up, then put the head back on.

[frankr]

1954 25hp does not have an o-ring around the upper bearing. Check the vacuum passage between the bearing and intake manifold. It is supposed to suck any leakage back down to the intake. May be plugged up. I believe it is a mighty small hole at the bearing.

I’ve installed many Heli-Coils in heads with no problem. But I’ll defer to other opinions. BTW, you better have a mighty accurate torque wrench if you are going to tighten the plugs to 20. Just a tad more will strip them, especially if the threads are worn. This is one place I will bend and tighten them by feel.

[dan-in-tn]

The part #592984 is for the cylinder head. New ones are available from Me and on Ebay. Pricey or best offer on Ebay/ free shipping. The guy has three of them. I’m with Frank torque values are 17 1/2 to 20 1/2, but I am just a feel kind of guy with plugs.

Dan in TN

[fleetwin]

quote OLCAH:

Fleetwin, If I change the head now would I have to disturb the head/head gasket later when I replace the print at the bearing? Looks like I would not have to per t2stroke . I replaced the upper carbon seal this winter with a new carbon and replaced the inner ring with the square type as recommended by Frank. After using it a few times I found fuel leaking in the seal area and running down on to the motor. So a couple of weeks ago I pulled the seal apart again and put in the factory recommended oring. I ran the motor (skipping) for a few minutes and oil was in the seal area with that also. Maybe the O ring around the bearing is bad.
I have an Rd15A with the same problem.

Frank accurately points out that this engine might not even have an oring around the bearing. So, I would definitely look closely at the correct parts book before ripping the crankcase apart needlessly. Follow Frank’s instructions about making sure the vacuum port is clean/operable, or else the fuel/oil that is drawn up to lube the bearing will just puddle there.
And again, not quite sure just what you are asking me so let me know if I miss the boat here. I think you are asking if the cylinder head must be removed in order to split the crankcase, correct? The powerhead must be removed from the exhaust housing, BUT the cylinder head does NOT need to be removed in order to split the crankcase halves.
Again, please look into this much further by using the correct parts book/asking questions before splitting the crankcase needlessly. I don’t have access to the parts book for that engine. Are you sure you installed the carbon seal correctly?

[frankr]

Here ya go…

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