Cross threaded spark plug in 50cc 4 wheeler

[paulharvey]

My mother in law just baught a old used 50cc Chinese no name 4 wheeler for my son. It ran when she bought it, and for maybe 5 minutes the next day. Then it died. So, yesterday, I put fresh gas in, checked fuel flow (good), put brand new battery in it, and checked the plug. When I put it back in, it went fine about half way, then it started feeling cross threaded, took it out, back in right, and right before it gets tight, it will just spin.

So, I think, but it doesn't matter, it was already crossed when I took it out, but whatever, threads are jacked now. It I believe is a 10mm x 1.0 thread plug, and I plan to get a heli-coil or similar.

My question is, do heli-coil (and other brands) need to use there own taps with the kit ($35 or so) or can I get a 10mm x1.0 tap ($6) and the thread repair ($5).

Never used any of these thread inserts before.

My thought was
1; tap would be cheaper then kit
2; I could try cleaning threads with the tap first, and maybe (cross fingers), just maybe get enough threads to firmly hold and seal the plug

 

[davesl708]

You will need to oversize the hole to make room for the heli-coil. You will need to use their threader to get the right match. Install the coil with thread lock to keep it from coming out the next time you remove the plug.

You are best to remove the head when you do this. Will need to have a new head gasket available.

 

[Soundguy]

I would skip the heli coil and use an actual spark plug repair kit.

there are many types.

You Might even just bore and tap for a larger plug.. that would be the best fix.

other possibilities are available.

being able to remove the head would be nice.

 

[jaotguy]

if removing the head is impossible ( or you don't want to do it ) , crank the engine till the exhaust is closed and the intake is open ... then put a vacuum cleaner hose ( exhaust blowing side ) to the intake of the carb and duct tape up , crack the throttle and tape in WOT position ...

turn the vac on and remove the plug .... air should be rushing out of the plug hole ... drill and tap / repair plug hole ....

the metal pieces should be blown out and away from the engine while you perform the surgery ....

 

[paulharvey]

Looks like my cheap butt is going to end up ordering on of the ~$35 kits on ebay. O'Reilly's cheapest kit was $138... I knew better than to get in a hurry, but I got in a hurry anyways...

 

[the old grind]

Solid inserts do work much better than coils, stay put better with locking compound. BTDT with Harleys, iron heads (Sportster) easier by far than alum ('big twin'). My insert tap has hex head, a long 'lead', and reaming section for new threads, so can be done (carefully) by hand.

Kit should include proper tap as with Heli-Coil and others. ($138? how many in the kit?) Removing plug from a 'hot' alum head is a recipe for disaster. Anti-seize on plug threads minimizes galling, but it's easy to over-tighten and strip them out completely. (where OP's PO left him?)

Tapping the hole for a larger plug would require drilling/reaming to proper size beforehand and finding the right heat range to use (by trial & error). Must retain enough sealing surface and clear cooling fins, etc. Get lucky the first time, as do-overs aren't assured with alum.

Mig-welding, drilling, and re-tapping the hole* might be worth the trouble and expense (my pick for this, esp if a 'short reach' plug) ... or seen as a last resort if inserts fail. Shops weld up lots of holes in alum to be re-drilled/tapped. (IMO worth doing.)

(*setting up coaxial to the original hole is the only tricky bit)

OP, 'Murphy' will be with you all the way on this, so tread cautiously and do it once. tog

 

[paulharvey]

Just ordered tap and inserts for $14 or so odd dollars on ebay. Estimated arrival is Oct 29, which is longer then I wanted to wait.

I have a funny feeling that this "gift" is gonna end up costing more then I expected.

 

[SimS]

If you try jaotguy's technique with a shop vac, make sure you don't have any gas in the carb. IMHO you could just grease up your drill and tap and go slow. The grease will trap the majority of any chips. You should be okay if you're using a kit. OTOH if it is screwed up too badly ebay has parts for those Chinese motors. I've seen cylinder heads for less than $30. Good luck

SimS

 

[LD1]

I agree with soundguy. Go to the next size plug. 10x1.0 is the smallest sparkplug threads. Go to a 12x1.25 and forget inserts and repair kits.

 

[Soundguy]

Solid inserts do work much better than coils, stay put better with locking compound. BTDT

agreed. My preference if the original hole can't be re-used or oversized.

Tapping the hole for a larger plug would require drilling/reaming to proper size beforehand and finding the right heat range to use (by trial & error). Must retain enough sealing surface and clear cooling fins, etc. Get lucky the first time, as do-overs aren't assured with alum.

I've done this on tractors. Of course, I don't know what he has to work with for a head.. It may be doable or not.. I just tossed it out as a possibility.

If it is an aluminum head... the 'tig' possibility may be just as easy / better results.