Any reservations using a thread insert?

[HankB 16]

I spent some quality time with our non-runner earlier today. After a compression test that ran consistently at 60 psi, I discovered that the plug threads were stripped out of the head. I could screw the comp tester in hand tight, but I doubt I had a decent seal. When I tried to reinstall the plug, it never tightened.

When I spoke to the tech at a local shop, he advised replacing the head rather than using a thread insert. He claimed that the insert would just blow out due to the heat experienced on this type of engine.

I'm curious what others have experienced WRT thread inserts. I understand his point, and the plug on this one has only 3/8" thread depth to begin with. On the other hand, his business is making repairs that the shop can stand behind, and on equipment that will see much more use than this lawn mower.

Any strategies for getting a more secure fit? Would red Loctite make a difference?

The engine, BTW, is a Tecumseh VM80 (8 hp, vertical shaft) from an '75 A-80-E.

thanks,

hank

[Cody 267]

I'v used helicoils in the past and have never experienced any further problems. They seem to be holding up good and i'v changed spark plugs several times sense.

[HankB 16]

I'v used helicoils in the past and have never experienced any further problems. They seem to be holding up good and i'v changed spark plugs several times sense.

Hi Cody - thanks for the reply.

Do you think the brand makes any difference? Amazon has several including Perma-Plug for $18.80 and Helocoil for $24.45. I'm thinking either would be fine but figure better to ask.

thanks,

hank

[W9JAB 156]

:notworthy:

Heli-coils work great but you do need to use the proper drill bit and tap! This is a must, never had one back out yet. :thumbs:

[pfrederi 17,146]

For the price of a helicoil set (drill bit, tap, coil and insertion tool) wouldn't a good used head be a better deal????

[HankB 16]

For the price of a helicoil set (drill bit, tap, coil and insertion tool) wouldn't a good used head be a better deal????

I don't know.

I've ordered this which comes to about $25 with shipping: http://www.amazon.com/Perma-Plug-1-25-Spar...59676714&sr=8-5

What woiuld a used head cost? What is the possibility that the threads in a used head be weakened? Where would I find a used head?

Would a used head require a new head gasket? If so, I might need a new head gasket anyway. Once I install the thread insert, if compression is not up to par, the next step is to pull the head to inspect valves. So I'm interested in the answer to that question regardless.

Good question and I do not have an answer.

best,

hank

[sorekiwi 761]

I've never used a helicoil on a tractor engine, but I have seen them used on car engines (aluminum head) and they seemed to work fine.

You are going to make a lot of swarf putting that helicoil in. You will be drilling the hole oversize, tapping a new thread, and after you screw the insert in you will be breaking off a little "tang" that is used for screwing in the insert. All that stuff is going to end up in your cylinder. You might catch some of it with grease on the drill bit and tap, but I doubt you'll catch it all. And that little tang in particular would make a horrendous mess if it ends up in the bore or on the top of the piston...

I'd pull the head, and put the insert in on the bench. And I'd use a new head gasket.

I think I would rather helicoil the head I have rather than take a chance on a used head.

[pbradley68 1]

Just for others reference since you've already ordered from Amazon.....

A long time ago I had a NAPA Auto Parts that has a machine shop do a Helicoil for me on an automotive head and it worked great. I don't recall the price but I'm pretty sure it was reasonable. I was having poor luck with the project at the time so I didn't think it was wise for me to attempt to do it myself then. :notworthy:

[WH nut 553]

I tried helicoil on my 7hp Kohler a couple times and It never held, Too much heat I believe. I had one head welded and tapped and got another head off Ebay. You can pick them up for 10 bucks if you look for them

[rickv1957 70]

I have used Heli-coils many years and never had a problem,Rick

[TT-(Moderator) 1,127]

I might use a Heli-Coil in a blind hole, but never for a spark plug. They have the ability to screw out of the bottom of the hole and into the cylinder if they come loose while installing the spark plug. That's not really a big deal on a "lawnmower" engine, but it absolutely STINKS when it happens on an automobile engine.

Solid (not wound wire) inserts with a flange or shoulder to keep them from screwing through the hole is a better way to go - along with thread-locker on the outside of the insert and copper high-temp anti-seize on the spark plug threads.

Good reading at the Timesert website.

Another option on stripped 14mm spark plug holes on many small engine heads is to drill it out and tap with 18 X 1.5 mm threads. (providing there is enough room for a seating surface) An Autolite 386 or NGK A6 (or a Champion D16) plug can then be used without an insert.

[linen beige 14]

Well said TT.

I was trying to remember the name of the Timeserts, but kept drawing a blank.

[W9JAB 156]

:notworthy:

If i'm thinking right, the head is a thru-hole and the block is tapped.

Also for spark plugs there is a insert with four pins that after you

tap in the insert you drive in the pins, for alum. only, but it will stay

were ya put it.

http://www.newmantools.com/key.htm

[kpinnc 10,715]

Another concern with inserts is to be sure you drill/ tap the hole perfectly straight. I have one that has a bit of a "lean" to it, and the plug wont seal properly, which defeats the whole purpose.

Kevin

[KC9KAS 4,741]

I work for a "major" automotive drive train remanufacture, but in the waste water & environmental department.

Our people use Heli Coils all the time, and if installed correctly, there are no problems. You actually use a "tread locker" on the threads and they stay put.

And by all means take the head off, do the repairs, and install a new head gasket & torque it to manufactures specs!

[HankB 16]

I work for a "major" automotive drive train remanufacture, but in the waste water & environmental department.

Our people use Heli Coils all the time, and if installed correctly, there are no problems. You actually use a "tread locker" on the threads and they stay put.

And by all means take the head off, do the repairs, and install a new head gasket & torque it to manufactures specs!

Hi Ken,

There was no question about removing the head. I could see the valves just beyond the spark plug thread and I sure didn't think there was adequate clearance for the repair tap. I felt better about doing that anyway. This kit called for high temp RTV and I already had some on hand for another project so I used that. I went with Perma-plug which uses a machined insert rather than a coiled wire so hopefully it will be sufficiently well anchored to hold. In addition, the upper threads are knurled and they include a tool to swage the knurled part into the hole.

I cheaped out on the head gasket though. When I pulled the head, I found a pretty badly scored cylinder. At this point my main goal with the engine is to get it running well enough to evaluate the transaxle. If the trans seems solid, I will probably look for a replacement engine or parts donor for this one and then I'll do a proper job.

In addition, I found anti-seize on the head bolts. Is it standard practice to anti-seize these? I would have thought not. I do know that it affects the results from torquing the bolts. Since the anti-seize lubricates the threads, it will result in greater tension on the bolt and threads for a given torque and that's not a good thing when the threads are aluminum. I found a torque spec of 40 lb-ft (seemed high to me) and went to 25 lb-ft.

Thanks,

hank

PS: My fishing buddy works in air and water, mostly in the steel industry. At one point he was chief turd herder for the plant at (what was then) Inland Steel, a fact I remind him of whenever I get the chance. :notworthy: