Help needed in figuring out lawn mower repair

[Multigunner]

I have a lawn mower with a Kohler XT7 engine.
The spark plug threads were never very sound and are now cross threaded for the last time.
I'd been able to trim the crossed threads out when this happened before, leaving most of the threads intact, but theres no fixing it now.

I've looked up the various thread repair kits with inserts, but the thick head and odd angle of the spark plug hole makes this look to be very difficult to do properly.
The odd angle of the plug and poor access to it is the main reason I kept getting it started wrong.

Is there any way to simply thread this head for a spark plug with a larger shank?
The present plug is a long shank 14 mm.

I'd be more than happy to pay some one to install a thread repair insert, but no shop I've contacted wants to do this. The mower is in fair shape otherwise but not in such great shape that I'd want to invest in a new cylinder head.
The alloy of the original head seems to be less than durable when it comes to the threads.

[stephenj]

Once you get the head off i doubt it will look quite as intimidating ... and yes the head has to come off .

Once you have the head off and the insert instructions in your hand it will tell you what size drill you need for the tap

When you drill the hole some care will need to be taken as you will probably need to use a hand drill .

I highly recomend step drilling it
Start with a drill that will barely cut the existing threads and if possible use two or three sizes inbetween that and the proper drill to finish for the tap .

Then tap your hole

Use lots of wd 40 for both operations ...

And remember ... never remove a plug on a hot engine with aluminum cylimder heads .


If my 15 year old nephew who has no business with any tools in his hands can do this on a dirt bike any adult can acomplish it as well

[SODAPOPMG]

Take it to a repair shop to have it fixed using either a helicoil or a keensert they will have the high quality tools to do the job right and will
probably cost the same as buying the repair kit yourself the good repair kits are expensive
the cheap kits are just that, and the repair insert comes out with the spark plug every time you remove it
this can be done without pulling the head but most shops will require head removal to be sure no chips are left inside
also try independen small engine shops,independent motorcycle repair shops shops,even automotive machine shops
because someone does this repair in your town/city just ask around

20 years as a harley mechanic and 10 years as a machinist

ps do not use wd 40 as another posted as it is not a cutting fluid use some tap magic or if it is aluminum you can get by using alcohol as a drilling and cutting fluid

[Goatwhiskers]

A suggestion: when you do get it repaired, put a little never-seize on the plug threads before installing. I've seen an awful lot of aluminum heads that seize to the plug threads, when you remove the plug the threads come with it. GW

[bdicki]

Thread repair kit about $30 new head $50. Take it to a repair shop that already has the repair kit.

[dagger dog]

K&D tools makes a thread repair "kit" that includes the over size tap, that matches the external threads on their insert, you have to measure threaded portion of the plug for length, then you can get the correct length insert. These are not the Helicoil type but rather a full insert.

Set the cylinder on TDC that way both valves will be closed, coat the tap grooves in heavy grease, this traps the shavings, the tap is extra long ( I've done air cooled VW engines with outremoving the sheet metal shrouds) and
you clean the grooves often and finish off with an air blast, so your Kohler should be easy.

You place the insert on the spark plug, apply a little red Loctite to the insert, place the spark plug ceramic insulator in a piece of rubber hose that grips fairly tight, and use that to install the plug with the insert on it, the rubber hose will let the plug center without cross threading. Then you torque the plug to spec's . Once the Loctite sets the steel insert will stay in the head.

I've used them on plugs that I couldn't see, the plus is now you have a steel thread.




www.mytoolstore.com
› Home
› KD Tools Index
2125 is the kit with the tap, you'll have to measure the plug to get the correct thread length.


I forgot , add a dab of anti-seize lube to the plug before threading on the insert.

[RED333]

If a head is 50 dollars, after you take it off, spend the time to fix it(maybe) or take to a shop for repair.
Not me, I would get a new head.

[bdicki]

14MM Cylinder Head Re-Threader Kit
2125
$38.49


Repair damaged 14mm spark plug threads by opening hole with a reamer/tap and screwing insert onto the spark plug. Use spark plug socket to install spark plug and insert. Remove plug and check that insert is properly seated. Set includes 1 each of 4 inserts: 3/8, 7/16, 1/2 and 3/4" reach and thread locking compound. Tap is designed for aluminum heads only.

[6bg6ga]

Put a helicoil in it and put it back together. You will never have to worry about it again. Done a lot of outboard motor cylinder heads in the past.

[troyboy]

Buy the new head.

[Multigunner]

Theres a decent automotive 14mm thread repair kit at Auto zone for less than 30 bucks. The inserts with that kit are full type with the seat for the washer, and teeth on the outer edge of the seat to be expanded to prevent backing out. They have a cheaper set by the same company for less than 20 bucks.

The type of plug this mower takes is also used by several automobile engines.

I have had the head off once already. First time it cross threaded I chased the threads back from the inside using the spark plug then trimmed away the ruined threads at the opening. That worked for awhile.

The seat for the washer seal has a chunk broken away, so a full insert with the seat is how I'd want to go.

While I found one site that listed the head alone at around 50 bucks the Kohler site lists this as a kit with all needed for replacement priced at 249 bucks, way more than the mower is worth.

If I could have found a local shop that would install the insert I would have already had it done.
Theres a motorcycle repair shop just down the road but they refuse to work on any thing other than motorcycle heads.

Too bad the original plug wasn't a 12mm, rethreading to 14mm would have been easy.

Heres the way it looks to me at this point.

Due to the odd angle of the plug hole I'll have to bolt the head to a block of wood with the upper surface cut to compensate for the angle. That way I can use my drill press to drill the hole out neatly.

I could also chuck a large bolt head down as an arbor and use the press to keep a steady pressure on the tap while I turn it.

The mower seems to be running okay now, the plug hasn't popped out at least.
I'll probably go ahead and get a new head before I'm through with it, if I can get one for 50 bucks. I may put this off till next spring, won't be needing the mower much more this year. The plug should hold and I won't need to remove it for cleaning anytime soon.
I've considering getting a smaller cheaper push mower, this mower is bigger than I need for my yard. The big walk behind mowers are fine when you are moving straight ahead, but are bulky and awkward when turning and weigh twice as much as the smaller mowers and cost three times as much.

[country gent]

The block of wood with the angle cut on it is a great Idea. Catch hole with a snug drill and clamp down to table. Drill to tap drill size for insert. I perfer the solid inserts, means bigger hole but when locktited in they very seldom back out I have had helicoils back out with the plug or bolt. If your chuck opens enough you can chuck the tap up and turn with a pin that fits the key hole tight. Or a point and small wrench. Use beeswax or black sulfar oil on drill and tap. Also lightly chamfer hole in head before tapping and installing insert. Clean with solvent both insert and tapped hole. You want the red locktite to get a good bond here. Coat first few threads of hole and insert with red locktite and assemble using a tapping type motion 1 turn in 1/2 back ect ect. This works the locktite into the threads and creates a solid bond. The inserts with the seat offer another advantage as they can be set by staking along out edge of insert seat with a punch.

[country gent]

Another thought If the table on your drill press rotates it can be rotated to the angle with out the block. Yse a long 14mm bolt and level.

[oldred]

Bear in mind that when done properly (not hard to do at all once the head is off) the repair will actually be better than a new head since it will have much tougher threads with that insert. Also as already pointed out a good thread cutting oil such as Tap Magic is very important for cutting clean threads for the insert, WD40 or most any penetrating type oil is about the last choice for cutting threads since they consist mostly of solvents instead of lubricant and can actually cause galling of the threads. If a true cutting oil is not handy then Kerosene or even diesel fuel works better than nothing. Finally the already suggested use of anti-sieze (I prefer the Permatex Copper high temperature) is a real lifesaver for those plug threads, I never install spark plugs in anything anymore with anti-seize even if they are going into a cast iron head. Anti-seize is a world-class problem preventer!!!!!

[bdicki]

http://www.powermowersales.com/p/Kohler-Engine-Parts#/s/KOH/XT7/head/1

[DougGuy]

Part of the problem is if there is any thread that comes all the way through the threads in the head they can get carbon deposits in the combustion chamber on the thread, then when you go to unscrew the plug, this carbon destroys the threads on the way out. After you get it fixed, check this out and use a plug that doesn't have a thread that protrudes into the combustion chamber or you can double the washers on it, use a different style plug, etc..

[leeggen]

Find one of the handy dandy lawnmower small engine repair shops and buy a used head for it. Just check the threads in the plug hole to make sure they are good.
CD

[HangFireW8]

Never use wd40 stoddard or kerosene alone for drilling or tapping Al, mix with oil or better yet use a proper liquid for the job like tap magic, relton or acculube.

[stephenj]

Ill be quite honest .. if it was my mower and the plug is staying in place .
I would be very tempted to leave ot alone for the rest of the year .
And next year put a new plug in with a bit of high temp epoxy and run ot till the plug fouled or blew out and worry about it then

Small engines just plain suck ... its likely to develop another problem you dont want to fix long before that plug fouls or pops out

[autofix4u]

Ill be quite honest .. if it was my mower and the plug is staying in place .
I would be very tempted to leave ot alone for the rest of the year .
And next year put a new plug in with a bit of high temp epoxy and run ot till the plug fouled or blew out and worry about it then

Small engines just plain suck ... its likely to develop another problem you dont want to fix long before that plug fouls or pops out


This is what I would do. That said I have installed many dozens of thread inserts in cylinder heads, from lawn mowers to V10 Fords. All have worked well.
As a much younger man I galled the threads on the cylinder head of my 1984 Kawasaki Bayou, when it leaked combustion gas around the gasket I pulled the plug and put good old J B weld on the threads. Sill have the bike 21 years later and J B weld a couple of new plugs in since. I WILL fix it right one day or the old bike may give up the ghost from some other ailment.

[Cap'n Morgan]

One word: Helicoil.

[HangFireW8]

One word: Helicoil.

A better word: Time-Cert.

[oldred]

Never use wd40 stoddard or kerosene alone for drilling or tapping Al, mix with oil or better yet use a proper liquid for the job like tap magic, relton or acculube.



Actually just plain kerosene works really well for threading aluminum, of course a proper threading fluid is always the best choice.

[Multigunner]

Doug guy wrote
[quote]
Part of the problem is if there is any thread that comes all the way through the threads in the head they can get carbon deposits in the combustion chamber on the thread, then when you go to unscrew the plug, this carbon destroys the threads on the way out. After you get it fixed, check this out and use a plug that doesn't have a thread that protrudes into the combustion chamber or you can double the washers on it, use a different style plug, etc.. [/quote

Thatsv exactly what these plugs do, by design not by accident or the wrong plug.
Where the hole comes out inside the head its at an angle and into the curved surface so half of several threads were exposed when the plug was fully turned home.
That looked like a poor way to design that head and asking for future trouble.

I appreciate the advice and links. I'm going to put off rethreading this head for some time, maybe till the plug works loose if its going to or the plug goes stone dead for some reason.

The stripped head in the link will require transfering all the valve parts. That shouldn't be too difficult. Unlike a flat head engine the head alone is not a ready to go item.

I do still intend to buy a smaller push mower, either on a year end sale or a good used one, as a spare if nothing else. More than likely I'll end up using the smaller mower and set the walk behind aside as a spare and only work on it when I've got nothing better to do.

I remembered a friend I haven't seen in years. He was always picking up discarded mowers and tinkering with them. He may have a otherwise unsalvageable mower of this type or know where I can get used parts from stripped junkers..

Thank you all for your interest in my problem.

[oldred]

That Heli-Coil or other insert will not only result in much more durable threads but will also correct the exposed thread problem, the outside of the threads on the insert would be exposed but will never be removed anyway and would still protect the threads on the plug. Just make sure the insert extends to the end of the plug threads but doesn't extend into the chamber any farther than the plug normally would and it will result in eliminating this obvious design error. Simply replacing the head would not change much since the original head with a properly installed thread insert would be much better (and a LOT cheaper) than a new or used replacement head, both of which would still suffer from the same flaw.

[MtGun44]

Take it to a good shop and have a helicoil put in. If done right, it will be stronger
and more resistant to cross threading than the original - literally better than new.

Bill

[Multigunner]

If not for the chunk missing from the mating surface for the sealing washer I'd consider the helicoil. The full insert has that surface as a flange with cleats to prevent backing out when removing a plug.

I hope to get this mower back in safe reliable condition whether I use it any more or not.
I'll be getting a smaller mower thats better suited to my yard anyway.
When its working properly I may give this walk behind mower to my niece, her yard is mostly steeply sloped. She loaned me her small mower when mine wouldn't work. Mowing her yard with a small push mower would be quite a job. I mowed it for her a couple of times years ago and even with front wheel drive it wasn't easy.

[MtGun44]

The inserts often back out unless they are pinned. Strongly recommend putting a notch in the edge and then
drilling an undersized hole and driving in a small pin made from piano wire, about .060 is good. Drop of
red Loctite helps, too. I had a few aluminum heads sp plug holes repaired different ways back in the 70s when
I was running the old aircooled VWs. Machine shop installed helicoils were the best fix, never had one give trouble.
The inserts with notched edges came out essentially every time until I pinned the last one. It stayed.

On critical threaded fasteners in some "high value" military hardware I used to work on, helicoils were often
installed during the manufacturing process to ensure that the aluminum threads never gave trouble over
the long service life of the equipment.

Bill

[6bg6ga]

I will have to disagree with the red loctite because there is enough heat to break the bond rendering it ineffective.

[oldred]

I agree the red Loctite will not take the heat without breaking down, I once loosened some Loctited screws in a chainsaw by simply running the engine until it got hot. If a Heli-Coil is used there is a better Loctite product for that, Loctite 271 Stude-n-bearing mount, it will take the heat and you better have the part/fastener where you want it if you leave it 30 minutes (the safe working time) or longer because it will take some serious heat to remove it!

There are much better inserts available than Heli-Coils, some use interference threads and some use attached wedges that are driven into place after the insert is installed. Heli-Coils are popular because they don't require enlarging the original hole very much and so they can be used about anywhere, the better inserts are much thicker and require drilling a bigger hole that often thins/weakens the part too much but in this case with the head that's not a problem at all. Autozone and other parts dealers have a sparkplug thread repair kit (less than $30) for that infernal Ford Triton engine that is plagued with plug hole problems (among other thing$!) but I don't know if they sell them individually or not. In any case they are several fairly cheap and much better insert alternatives available than Heli-Coils for fixing the threads in one of these Aluminum heads.

[Multigunner]

Since the seat for the sealing washer has a chunk broken away Helicoil won't cut it. I wish it would but it won't in this case.

I was thinking of locking the insert against backing out by counter sinking at the edge of the seat and threading for a locking screw like that used for a Mauser action floor plate screw. That would also insure a good ground if whatever form of locktite I used formed an insulating barrier around the threads.
Also since I'll be taking the head off while I do this I may be able to upset the exposed edges of the insert on the inside to prevent it unscrewing.

[oldred]

While that would certainly work it's actually a lot of unnecessary work, one of the interference thread type inserts would work just fine even without thread locker although a bit of thread locker would be added assurance. The pin type would be even more secure and it would actually be overkill in this situation since those darn things would be very hard to get out even if you wanted it out!

[ncbearman]

If its only $50- New Head (and gasket)

[oldred]

If its only $50- New Head (and gasket)


The insert would not only be cheaper it would be MUCH better than a brand new head! The new head would still suffer from the same design flaw with soft aluminum threads and sparkplug threads being exposed to chamber gasses, the insert would eliminate both of those problems.