Topic: Spark plug hole threads are stripped. What do I do?

[Dr. Honda]

HELP!

My threads for my spark plugs are stripped on the engine.  I've never had plugs in it, it did not run when i got it.  Now the motor has been rebuilt, and I put it back together, well, I was about to degrease it to prime and paint and I was screwing my plugs in so not to get anything in the engine, the last one was stripped from previous owner.  What is the lowest tech, non-honda repair shop way to fix this.  I really dint want to take the motor apart.  I figured run a tap in, but then the pieces of aluminum would fall into the valves.  Or either place some thin wall aluminum tube into the hole an tighten a bolt with same thread pitch and size into the hole.

What do yall think?

[crazypj]

You can get 'Recoil' which is pretty much same as Helicoil but cheaper.
Pep-Boys, Autozone, et.al. about $35.00.
 Why wasn't it fixed while engine was being re-built?
If it wasn't checked closely enough to see stripped thread, I wouldn't trust rebuild

[camelman]

Take the head off and do it correctly.  Don't use a cheap helicoil either.  The sparkplug will not seal against a cheap helicoil, and you will get blowby every time that cylinder compresses and/or fires.

You might be able to reuse your cylinder head gasket if you haven't heated it up yet.  I'll let others weigh in on that though.

Camelman

[dave500]

the head gasket will be ok,pull the head and fix it or get it fixed.

[katmol]

If the bad threads are not very deep you can get a tool called "BackTap" that works like a charm. I just bought one on Ebay for $10 and it worked great! I repaired plug hole #3 with the head on the motor and the motor in the bike. You insert the tool all the way into the plug hole then turn the knob on the back of the tool, this makes the cutting head expand to fit the plug threads. As it snugs up, carefully keep checking that the threads are aligned by screwing it back and forth a little each time you tighten it. Once it's positioned you just carefully unscrew it and it repairs the buggered threads as it comes out. It good to put a little grease on the end to help with the friction and it helps to hold any cuttings. There should be very little cutting involved since you are just straightening out the threads. Worked great for me. Kept me from pulling a motor.
  

HELP!

My threads for my spark plugs are stripped on the engine.  I've never had plugs in it, it did not run when i got it.  Now the motor has been rebuilt, and I put it back together, well, I was about to degrease it to prime and paint and I was screwing my plugs in so not to get anything in the engine, the last one was stripped from previous owner.  What is the lowest tech, non-honda repair shop way to fix this.  I really dint want to take the motor apart.  I figured run a tap in, but then the pieces of aluminum would fall into the valves.  Or either place some thin wall aluminum tube into the hole an tighten a bolt with same thread pitch and size into the hole.

What do yall think?

[dave500]

if the threads are so stripped that a plug wont tighten up remove the head.,you wont rebuild threads by trying to retap them like that.

[katmol]

That is correct if they won't tighten up. But if they won't screw in, it certainly worth a try I would think.

if the threads are so stripped that a plug wont tighten up remove the head.,you wont rebuild threads by trying to retap them like that.

[dave500]

if they they wont even screw in,reaming them is only going to result in tears,pull the head.Dr honda states the threads are stripped,give it a go and pull the head later.

[cookindaddy]

A helicoil (or a reputable competitor and there are several) properly done is as good as the original. Any engine re-builder can put them in for you. I have two in mine. The compression is great and the bike goes like hell. You should pull the head.

[dave500]

you can be as carefull as you like,some chips WILL fall into the bore,pull the head.,they might just all blow out on the next fire.then again they might not.

[nokrome]

http://www.timesert.com/ makes a product that is specifically designed for spark plug holes, the kit is a little spendy but it is by far the best product for this application imo.
   oh, do yourself a favor and take the head off before you attempt the repair, its really not that big of a deal

[katmol]

They're right, I'm wrong. Since the motor's out do it right, pull the head. Sorry.

[crazypj]

I would only use copper plated Timesert inserts, they are designed for spark plug hole repair.
 The plugs don't seal on the threads so it doesn't matter what type of insert you use.
 Don't use any threadlocker, that's only used by cowboys who screwed up and are trying to 'glue' inserts in place

[Duanob]

If you use a tap coat in thick grease. this will catch 99% of the shavings.

 
Someone wrote:
" The sparkplug will not seal against a cheap helicoil, and you will get blowby every time that cylinder compresses and/or fires"

Say Wha? I tapped and helicoiled my ford truck and I've put 10,000 hard miles on it no problems since. Including a trip halfway across the US and Canada @ 14 hour days and towing my boat 1000 miles roundtrip over two mountain passes each way. And the timesert is nothing more than a fancy over priced helicoil (same idea same result) but at 10X the cost.

The one good thing is the SOHC4 head is relatively easy to take off, unlike my F150.

[the technological J]

what kind of bike? you can get a new head gasket( if need be) for a 750 at cyclex for 8 bucks

[sangyo soichiro]

Just a FYI from a former tool and die maker...
(This is just an aside, and not necessarily anything to do with Dr. Honda's problem.)

You guys are talking about chips from the tap falling into the cylinder.  There's a kind of tap called a "roll tap" that pushes the metal (as opposed to cutting it).  It makes for a stronger thread, but the hole being threaded should be a softer material (like aluminum).  Here are two pictures so you can compare the two types of taps.

Roll tap (forms the thread by forcing the metal outward):


Regular tap (cuts the thread):

[cookindaddy]

Interesting about the roll taps. I'd never heard of those. I haven't started looking yet, are they readily available? Would they be good for chasing threads to clean them up? In that case I'd try to find M6 and M8 since that's 90% of the bolts on the SOHC4. I have been running a regular tap through rusty threaded holes with good success although some here say that you shouldn't use a tap for that. Those would be mostly steel threads.

[katmol]

If you're going to try a tap please looking into to the Back Tap.

Interesting about the roll taps. I'd never heard of those. I haven't started looking yet, are they readily available? Would they be good for chasing threads to clean them up? In that case I'd try to find M6 and M8 since that's 90% of the bolts on the SOHC4. I have been running a regular tap through rusty threaded holes with good success although some here say that you shouldn't use a tap for that. Those would be mostly steel threads.

[sangyo soichiro]

Yes, I think they are readily available, although I haven't used one since my machinist days so I never went looking for one.  I suppose if you're just chasing threads, these would be good, but I'd try to make sure there's no dirt and junk in the threads.

[sangyo soichiro]

If you're going to try a tap please looking into to the Back Tap.

http://www.jegs.com/i/JEGS/555/80595/10002/-1?parentProductId=954483

[katmol]

Ebay $10 It's a Napa tool
http://cgi.ebay.com/ebaymotors/Back-Tap-12mm-Int-Spark-Plug-Rethread-Tool-3689-_W0QQcmdZViewItemQQhashZitem51864aef27QQitemZ350145408807QQptZMotorsQ5fAutomotiveQ5fTools

If you're going to try a tap please looking into to the Back Tap.

http://www.jegs.com/i/JEGS/555/80595/10002/-1?parentProductId=954483

[Dr. Honda]

It's a 72 cb500 k1

what kind of bike? you can get a new head gasket( if need be) for a 750 at cyclex for 8 bucks

[Dr. Honda]

Kind of a silly question i think,  but I know i use an 18mm socket to tighten my spark plugs.  The repair kits for the threads are different sizes, i guess this means i need one for 18mm plugs, right?

[scottly]

The socket size is not the same as the thread size. (Sorry, I don't know the thread size off the top of my head, but I think it's about 12mm.)

[crazypj]

Roll taps come with Timeserts.
 If it isn't lubed properly you will be in much worse shape