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MG TD TF 1500 - Tap Cleaning out Engine Threaded Holes

I am starting a thread to warn against using a standard tap to clean out engine holes. No matter whether you use a bottoming tap, a plug tap or a taper tap, it will not only remove dirt and debris, but WILL remove metal and re-cut threads when you use it on an existing hole. Despite the temptatikon to do so, a regular tap should never be used for cleaning out a hole.

Only a special "Cleanout tap" should be used for this purpose, one that is designed to remove debris from an existing threaded hole without removing metal.

You might think this would be a minor or uncommon issue, but I sold a set of studs to an MG owner in Australia last year. He called to tell me that when he installed my ARP studs (see mgtepair.net) he was shocked when four studs pulled completely out of the block long before the recommended torque had been applied! It turned out that he had used a regular tap on the head stud holes, which had sufficiently weakened the threads to ruin their effectiveness.

At great expense I sent him an insert kit (I have a strong preference for Rock Solid inserts by Chrislynn) and he was able to drill, tap and install new inserts, but the wrong tap had caused a lot of unnecessary work, expense and hassle.

In a pinch you can take a regular tap and sandblast the daylights out of the cutting edges to soften all the sharp edges, and it will work acceptably, but it's not the most consistent or reliable solution.

Tom Lange
MGT Repair
t lange

Tom excellent point.

I would offer three other suggestions to help with this issue. First I keep those cleaner/thread chaser taps You use on engines in a separate colored and labeled ziplock plastic bag so as to not confuse the issue. Second, I bought a set of metric/SAE thread chasers only and labeled the plastic box so I do not reach for the wrong one and use real taps to chase. I find these easier to use as I get older because they have large ends for old fingers. Third, when it came to BSF I have not been able to find thread chasers so I will use your suggest of blasting them since I can find cheap normal taps on the Internet.

Thanks for the reminder.

Joe

JWP Policastro

I cut a gash across the threads of a hardened bolt with a cutoff wheel on my grinder to create a shade-tree-mechanic clean-out tap. Not as good as the real tool, but better than double-cutting treads with an incorrectly positioned tap (which I have done.)

Lonnie
TF7211

LM Cook

Is there a list of recommended cleanout tap sizes?
Is there a recommended place where they can be purchased.

Thanks,
Sherman
Sherman Kaplan

Lonnie - Birds of a kind - I have a whole box full of home made clean-out taps. I learned this from the old German machinist that we had working in the electronics shop (yes a machinist is always needed, even in electronics shop) while working at the Puget Sound Naval Shipyard. Cheers - Dave
DW DuBois

Sherman

I you looking for tapes for the engine or body or both? Engine is metric; frame BSF.

Joe
JWP Policastro

I'm looking for the engine taps for cleanup/thread chasing.

Thanks,
Sherman
Sherman Kaplan

Google Thread chaser / restorer. I bought one from Home Depot for the rocker arm adjusting screws, it straightens the threads without removing any metal, about $8.
Abingdon Performance LTD.
Len Fanelli

Great advice Tom.
MAndrus

This is also an argument for using studs, not bolts wherever possible. It saves wear on the threads in the block. That said, I'm guilty of using bolts sometimes because of clearance issues removing a part from a stud. Water pumps come to mind.
Steve Simmons

Most of the threads on the engine are metric but not as we know them! The pitch on the metric threads used by MG when our cars were built is different to the one used today. If you simply buy modern metric taps and dies from a tool supplier you will damage your engine. The ones you need are M6 x 1.00 M8 x 1.00 M10 x 1.5 and M12 x 1.5. They are all available all you have to do is specify them properly. Normal BSF, Whit and BA will cover virtually everything else.


Jan T
J Targosz

Some of our strange threads are still in use in Japanese motor cars and motor cycles.
The taps and dies are still included in sets by Silverline sold by Toolstation in the UK.
Ray TF 2884
Ray Lee

you can get every tap and die you need from Tracey Tools - Google them. A M6 x 1 for instance only costs £2. I bought a full set from them when rebuilding the TF engine and a left hand BSF die when I damaged the thread on the front stub axle.

Jan T
J Targosz

This thread was discussed between 11/06/2018 and 13/06/2018

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