Threaded spark plug repair

spartacus · 02 March 2014, 12:18

Routine gear oil change on my Tohatsu M60C engine yesterday. Took a little longer as the fill cross head screw was seized. Heated it up and it came out fine.

Then onto the sparkplugs. The screw threads have never been quite right, and at some point someone probably cross-threaded them. Part of the reason I always thread them on by hand, then use a ratchet. They tightened up okay last season, but wouldn't tighten sufficiently yesterday.

On removing one of the sparkplugs, there were little metal shavings. Just great.

Screw thread is goosed on top cylinder, and middle one doesn't look great, so will need to fix both. I thought twice about removing the cylinder head, as I was wary of shearing bolts.This engine only ever gets used in the sea, so that was a distinct possibility. Pressed on and removed the cylinder head. The bolts were tight and had powdery residue when extracting. The gasket is in good shape and didn't stick to the cylinder face so can probably be reused. I cleaned both faces up. Cylinder bores are clean, no scoring. Water passages as you can imagine had salt crystals, so again, all cleaned up.

To repair the spark plug holes, what would you recommend? I've used Helicoils before (on a car) and has worked okay, however that was on a suspension strut (secured by another 2 bolts) not on a cylinder head. The depth of the hole on the cylinder head isn't huge, possibly 8-10mm. Should I be looking for a solid insert instead, such as V-Coil? Only trouble with V-Coil is then removing the excess material inside the head (smallest they supply is 12.7mm). Probably need to use a Dremel with cutting disc.

Engine is 2006.

Nos4r2 · 02 March 2014, 12:25

Try recutting with a tap first. Then Helicoil, then solid type insert unless it's really obvious you need to go straight to the solid type. I don't like any of the options much, but Helicoil is far preferable. Solid inserts are a recipe for white deposits round them. I've had bike spark plug threads helicoiled before and they lasted for a very long time..

Or find another head.

Don't resuse the gasket. For want of a nail, the kingdom was lost, etc.

spartacus · 02 March 2014, 12:32

Pictures. If you look closely there is cracking on the inside of the cylinder head bore. The spark plug thread could have been weakened before, as the outside of the head also had a little deterioration on the face of the plug thread.

spartacus · 02 March 2014, 12:34

No scoring on the cylinder sleeves.

spartacus · 02 March 2014, 12:40

Face of cylinder head. Note the top hole face deterioration, (left hand side).

Nos4r2 · 02 March 2014, 12:41

New head. I wouldn't trust that now if there's cracks appearing.

spartacus · 02 March 2014, 12:48

Quote:

Originally Posted by Nos4r2

Try recutting with a tap first. Then Helicoil, then solid type insert unless it's really obvious you need to go straight to the solid type. I don't like any of the options much, but Helicoil is far preferable. Solid inserts are a recipe for white deposits round them. I've had bike spark plug threads helicoiled before and they lasted for a very long time..

Or find another head.

Don't resuse the gasket. For want of a nail, the kingdom was lost, etc.

Cheers Nos. Just knew you'd mention the gasket. Honestly it looks fine. I was going to use a smear of Hylomar Blue gasket sealant, little marine grease on the cylinder bolts, tighten in sequence, etc.

It's all money just now. I've got a Helicoil kit on order, so will try that. Might know where I can source another head, but will try to repair first.

PeterM · 02 March 2014, 12:57

Helicoiled one of my opti plug threads. (I paid someone as it involves fuel rails and stuff) No problems...:-)

Defo a new gasket....it might look ok, but it will have been compressed so won't ever be the same.

As for the head...if you can see cracks...it's worse than it looks. Find another would be my choice.

Nos4r2 · 02 March 2014, 13:03

Quote:

Originally Posted by spartacus

Cheers Nos. Just knew you'd mention the gasket. Honestly it looks fine. I was going to use a smear of Hylomar Blue gasket sealant, little marine grease on the cylinder bolts, tighten in sequence, etc.

It's all money just now. I've got a Helicoil kit on order, so will try that. Might know where I can source another head, but will try to repair first.

It's been compressed once. Don't do it-sea water in bores won't be good.
Blue hylomar on a head gasket is a really REALLY stupid thing to do. (sorry, had to fix too many motors where it'd been done)

Waterman · 02 March 2014, 13:14

I used a spark plug helicoil kit before. Worked perfectly, just make sure you use the correct heat resistant loctite.

spartacus · 02 March 2014, 13:30

Point taken Nos. I've put an order in for the gasket. Part number 3F3-01005-0, probably in the region of £40.

Simply can't replace the head just now. I'm over on the west coast in a few weeks so will go to an outboard graveyard I know where Tohatsu's are reborn! Will see what he has kicking about.

spartacus · 02 March 2014, 14:40

Quote:

Originally Posted by Waterman

I used a spark plug helicoil kit before. Worked perfectly, just make sure you use the correct heat resistant loctite.

Loctite 272?

Waterman · 02 March 2014, 15:06

Yes Think it was loctite red 271 I used... No issues yet. I Kept a spare helicoil insert just incase it ever unscrewed with the spark plug.

Ribochet · 02 March 2014, 15:15

Quote:

Originally Posted by Nos4r2

It's been compressed once. Don't do it-sea water in bores won't be good.
Blue hylomar on a head gasket is a really REALLY stupid thing to do. (sorry, had to fix too many motors where it'd been done)

Head gaskets are a one shot item - what Nos said

Peter_C · 02 March 2014, 15:33

Heli-coils are CRAP!! They don't hold very well, and pull out too often. Not a permanent repair.

Time-sert's are the way to go for spark plug thread repairs, and are considered a permanent repair. ++ TIME-SERT Threaded inserts for stripped threads

Probably cheaper than buying a Time-sert kit would be to find someone with one and pay them to do it. Then again with the word cracking I would either be welding the old head or getting a replacement. Got a better picture showing the crack?

FWIW We always do the thread repairs with the motor together...and in the vehicle. Grease keeps the debris from falling into the cylinder (Hopefully).

spartacus · 02 March 2014, 16:56

Quote:

Originally Posted by Peter_C

Probably cheaper than buying a Time-sert kit would be to find someone with one and pay them to do it. Then again with the word cracking I would either be welding the old head or getting a replacement. Got a better picture showing the crack?

FWIW We always do the thread repairs with the motor together...and in the vehicle. Grease keeps the debris from falling into the cylinder (Hopefully).

I did think about leaving the head on, but bit the bullet and stripped it down. Ultimately easier to work on, although I've seen videos on youtube repairing it in situ.

I've looked at the time-sert kits which are expensive, but more substantial than a helicoil. If I use a time-sert it will need to be ground back inside the cylinder head so it's flush. There's a head shop in Aberdeen which charge £50 an hour. This might be the way forward as I can take the head to them.

Surface cracks and pitting. Nothing to suggest the integrity of the head is compromised.

nugent · 02 March 2014, 17:07

Quote:

Originally Posted by Peter_C

Heli-coils are CRAP!! They don't hold very well, and pull out too often. Not a permanent repair.

Time-sert's are the way to go for spark plug thread repairs, and are considered a permanent repair. ++ TIME-SERT Threaded inserts for stripped threads

Probably cheaper than buying a Time-sert kit would be to find someone with one and pay them to do it. Then again with the word cracking I would either be welding the old head or getting a replacement. Got a better picture showing the crack?

FWIW We always do the thread repairs with the motor together...and in the vehicle. Grease keeps the debris from falling into the cylinder (Hopefully).

100% recommended

Worth time serts. I used to build and race high comp quad bikes and used these as a std in part of the build. The high comp engines I built in the early learning days always stripped the head of there plugs due to high compressions ,, never happens with a time sert added,, not cheap. But good items never are,,

Peter_C · 02 March 2014, 17:38

Quote:

Originally Posted by spartacus

If I use a time-sert it will need to be ground back inside the cylinder head so it's flush.

The kit comes with a tool that removes enough metal to allow the Time-Sert to sit properly. No "Machine Work" is needed, just utilize the kit and it's contents...with grease! >>>Related more to doing them with the head installed. Stop and clean often not letting the chips build up! Before installing the insert, clean the newly cut threads to remove the grease used to keep chips from falling, along with any errant chips. There should be plenty of youtube videos on using the kit.

The head is really hard to see in the photo, but those almost appear like casting marks. If they are cracks

The head needs to be replaced, but more importantly I would worry about why the fuel mixture is so far off (Lean), in all the cylinders, causing it to run hot. If they are just casting marks, put it together and run it.

Locozodiac · 04 March 2014, 14:41

If you have already 2 shot out of 3 spark plug's threads, probably will be better to change all 3 Time Serts at once at a shop. Have used helicoils myself with no issues at all as long they are well bonded to head. Somebody stated that helicoils retains more heat on the surrounding area than Time Serts.

Head gaskets have their own sealing glue adhered to both sides, no good to use old ones as will be compressed and probably not seal combustion chamber 100%

Happy Boating

bosun · 05 March 2014, 20:28

The time sert kit that I've got has an assortment of different length inserts so that if you fit the correct one there is no machining to do.
I've fitted dozens over the years (mostly to cars) to do it in place wind the piston down from tdc so that the tap doesn't mark the piston, grease the tap, cut the thread,spin the engine over to blow any swarf out of the spark plug hole,clean the grease out of the new thread in the head with aerosol brake cleaner, allow to dry, screw a time sert onto a spark plug with your fingers, loctite the time sert thread ,(don't get it on the plug thread!!!!) screw the insert in to the head using the plug, nip the plug up to seat the insert, when the loctite has set, the plug can be removed if needed.
We used to coppaslip the plug thread on cars not sure about coppaslip on an outboard though !?