Plug thread
- Thread starter Paul Marx
- Start date
CLEMTOG
Hero member
as you say Paul, clean the thread with a greased tap, but then clean the grease out (piston at TDC valves closed) using brake cleaner and an air line, plus a rotary brush of some kind, 12 bore shotgun cleaning type in nylon would be ideal, you will make a mess, next clean the thread of the new plug, glue it in with bearing fit and tighten it as much as you dare, not nice, but will last until the next plug change, four years?
CLEM
CLEM
Thanks Clem,
Not so much a matter of plug change as taking the plug out to turn the engine over by hand when needed.
Paul
Jarvo
New member
- Location
- colorado up by the divide
Hi Paul a tap designed for cutting thread removes material permanently ! they do make tools to dress or repair threads that do not remove material as aggressively depending on the thread damage , a better option than a regular tap . I have been presented quite a few heads that have been owner repaired that are well damaged and needed machining to have a custom insert installed to remedy the situation . Some times the best solution even if just dressing the thread is the solution pulling the head putting it on the milling machine to have precise control of the angle of attack is just better to reduce damage regret and cost in the end . Of course having access to a machine shop helps and drives my opinion . Good luck Jarvo
Paul,
I've repaired quite a few auto heads by your decribed method, wasn't too concerned about a couple of chips in an old, tired Opel or Ford engine.
I've also installed a few Timeserts with the head still fitted. In the end, all attempts were sucessful! Most plug-repair taps have a lead-in with the original size thread to ensure a correct (or near enough) angle of attack. Timesert repair kits will clean up the plug sealing surface for the washer as well, a deviation of 1-2° won't kill you.
A thread chaser tool would also be my go-to for a first try. Luckily both the 500 plug holes are quite easily accessable and shouldn't pose too many problems. Inspecting the cylinder with an endoscope camera before buttoning up might help to find a stray chip or 2... that's when the fun begins.
piet
I've repaired quite a few auto heads by your decribed method, wasn't too concerned about a couple of chips in an old, tired Opel or Ford engine.
I've also installed a few Timeserts with the head still fitted. In the end, all attempts were sucessful! Most plug-repair taps have a lead-in with the original size thread to ensure a correct (or near enough) angle of attack. Timesert repair kits will clean up the plug sealing surface for the washer as well, a deviation of 1-2° won't kill you.A thread chaser tool would also be my go-to for a first try. Luckily both the 500 plug holes are quite easily accessable and shouldn't pose too many problems. Inspecting the cylinder with an endoscope camera before buttoning up might help to find a stray chip or 2... that's when the fun begins.
piet
Thanks Piet.Paul,
I've repaired quite a few auto heads by your decribed method, wasn't too concerned about a couple of chips in an old, tired Opel or Ford engine.
A thread chaser tool would also be my go-to for a first try. Luckily both the 500 plug holes are quite easily accessable and shouldn't pose too many problems. Inspecting the cylinder with an endoscope camera before buttoning up might help to find a stray chip or 2... that's when the fun begins.
piet
If I can avoid getting that head off again, I'll be pleased and so will the Ms.
Paul
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
Old school- get an old plug, using a grinder, grind three flats on the thread ( so it resembles a tap) then using a wire wheel on a bench grinder softener the edges of the existing thread. What you’ve got now is a thread chaser that isn’t sharp , so you won’t remove material - just redirect it in the original thread. Another trick is to carefully inserting it using copper slip - again to prevent material removal. You can of course buy a thread chaser, if anyone still makes them. I bought a Snap-on one thirty years ago. Copperslip new plug to help spread the load over the whole thread.
Thanks. I was thinking about the old spark plug trick.
But I've ordered thread chasers from Holland, likely made in China, and a set of 12x1.25 taps from Germany, likely made in Germany. From Baer, thanks Michael.
First, we'll ride the bike, starting tomorrow but I'll look into the plug thread before any longish trip is envisaged.
Paul
As a side note, "cutting" a thread with appropriate tap or die's requires cutting compound, some old school paste compounds were very effective. At college ( was a teacher ) various ill informed would use lubrication oil as a cutting assist, the antithesis as oil reduces friction.
Mention this as though being common knowledge, there may well be a perception that grease is a cutting assistant by some.
Recent car arrival here, one plug was alarmingly tight as i went to remove it, took me over an hour to slowly remove by way of ATF and Acetone mix, injected into the cavity when the plug seat seal was raised above the head seat, 1/4 turn at a time back and forth. On removal there was no actual cast aluminium swarf on the removed plug, thank goodness.
Studied the NGK plug thread form nothing was obvious, with the basic measurement tools here. Replacement plug was fine, could not chase the thread in the head as double ended plug chasers do not retain in long tube plug tool. Main concern with the long tube box drive, was not being able to start the chaser at the correct orthogonal position. j
Mention this as though being common knowledge, there may well be a perception that grease is a cutting assistant by some.
Recent car arrival here, one plug was alarmingly tight as i went to remove it, took me over an hour to slowly remove by way of ATF and Acetone mix, injected into the cavity when the plug seat seal was raised above the head seat, 1/4 turn at a time back and forth. On removal there was no actual cast aluminium swarf on the removed plug, thank goodness.
Studied the NGK plug thread form nothing was obvious, with the basic measurement tools here. Replacement plug was fine, could not chase the thread in the head as double ended plug chasers do not retain in long tube plug tool. Main concern with the long tube box drive, was not being able to start the chaser at the correct orthogonal position. j
Sir Sidney Ruffdiamond
Hero member
- Location
- Cotwolds
Look into Brisk plugs Paul - much more reliable for our classic bikes - made in Czech - no copies
Do they do Laverda 500 cylinder heads as well?
I admit to not feeling the need for more reliable plugs. I change them as a matter of course once a year, if I don't forget.
Paul
Timesert a straightforward process & let me add that it's extremely important after spark plug removal to bump the engine by hand to make sure both valves are off cam/closed. You don't want to run the tap into the edge of an open valve!
piranha-bro2
Hero member
- Location
- Melbourne
Pretty much irrelevant in this case, the 500 is a 4-valve, with pretty small valves at that! The 12mm plug is located centrally with lots of space between the valves.
Just need to take precautions to catch as much swarf as possible, if having to choose between cutting oil or grease, I'd go with grease. Patience is probably the most important factor, this is not a job to be rushed.
piet
CLEMTOG
Hero member
I was forgetting the plug thread size when I suggested a 12 bore shotgun nylon cleaning brush, that works perfectly for normal 14mm plugs, but for 12 mm plugs you will need a smaller one, I think 20 bore would be too big but .410" might be ideal!, available in brass or nylon. Timecerting can be tricky on any plug thread due to space around the hole, but I would do it, getting the thing square would be a challenge ,as it is with any plug thread, if its out of square, it can give plug gasket sealing troubles , the same goes for in situ drain plug repairs. I have all the 12mm Timecerting stuff Paul to save you from buying the kit for one thread, but this is breaking my rule of not lendng any thing to anyone, (was started about 3 years ago due to the behaveyer of the mechanics repairing what was at that Time "hairy biker" Dave Miles Jota) the relationship between you and I overules this, well, not you, but the lovely Corrine.
CLEM
CLEM
It's a cautionary point regardless of application & I should point out piston at BDC as well. I agree that grease in the tap cutouts is preferred vs a light cutting oil.
Andy J
Hero member
- Location
- Isle of Man
I’m glad to hear the operation went well. I fear I have a similar issue with my 350 and have been putting off doing the job in fear of making the situation worse. However, I now feel more emboldened by your success and will see if I can replicate it.