Ned :
In addition to possibly dropping crud into the cylinder, some people believe
that re-tapping will weaken the threads (basically by converting them from
rolled 85% threads to cut 100% threads).
I only chase the threads if they seem to need it (old plug came out hard,
new plug goes in hard, etc.), mostly because I'm lazy <g>.
Probably 98.9% of cars, trucks, tractors, boats, lawnmowers, etc. in the
world use the same 14mm plug thread, another 1% use an 18mm thread (Dad's
Packard did, I hear some new Fords do). I don't know the thread pitch
offhand, but many auto stores sell a "spark plug thread chaser" that has
both threads, and is designed to not undercut good threads. Sears lists a
14mm only (not Craftsman) on their web site for $4.99. It's designed to be
turned with a spark plug socket, no tap wrench required.
Please note that "plug tap" means something quite different, having nothing
to do with spark plugs.
The usual trick is to smear the tap flutes full of grease to try to catch
any chips, dirt etc. For just chasing threads, you shouldn't need any
cutting oil.
Randall
> -----Original Message-----
> From: owner-triumphs@autox.team.net
> [mailto:owner-triumphs@autox.team.net]On Behalf Of ewcorco@erenj.com
> Sent: Monday, March 20, 2000 11:42 AM
> To: triumphs@autox.team.net
> Subject: Plug Taps
>
>
>
> Listers:
>
> This probably has been covered at some point - if so,
> apologies in advance
> as I missed it......
>
> Recently a Toyota mechanic mentioned to a buddy of mine that
> at his shop,
> they run a tap through the threads to clean them up everytime
> they change a
> spark plug on a car, especially those with Al engine pieces.
>
> That seemed like a good idea to me, especially since I've
> occasionally seen
> a plug not thread back in as easily as it should during the
> lifetime of
> some vehicles.
>
> My questions - is there a down side to doing this (i.e.
> forcing a small bit
> of gunk/metal into the cylinder)? What taps would one
> typcially need to
> have on hand to be able to do this for a range of common
> plugs (i.e. my TR6
> through my Honda daily driver or my tractor)? How would one
> know what tap
> to use for a specific plug (is there some kind of chart)?
>
> Also, I'd appreciate a brief write up to use if someone could
> pass it on to
> me - i.e. whether or not to use a bit of tapping fluid or
> perhaps grease to
> immobilize any dirt, etc.
>
> As always, thanks in advance.
>
> Ned Corcoran
> 1971 TR6
>
>
>
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