Anyone know the thread pitch for 1.9TD cylinder head bolts?

[vwt4]

This probably sounds a weird question but I am currently rebuilding the top end of my 1.9TD ABL motor and have some new head bolts to put back in it.

The bolts are the same for 1.3 petrol, 1.6 derv/gas, 1.7 and 1.9

In other words many VAG engines!!

I am about to buy a bottoming tap to clean out the threads on the block so I get the right torque on the bolts for the cylinder head...

BUT , I cant find anywhere what thread pitch the bolts are?

They are M12 bolts

I have ordered a thread pitch gauge but dont want to wait as I need to order the tap

This is the one Im looking at


M12 bottoming tap
12mm x 1.75mm Pitch x 89mm Long

Will it work?

thanks

[Mark(The Miser)UK]

Just take a used bolt and measure 10 threads with a metric rule...
Use the same old bolt to clean out the threads. In any event don't waste your money with a tap :idea:

[theman53]

M12-1.75 is correct thread pitch, but I think some compressed air and brake clean might be a good option along with a clean bolt to run down to the bottom first to get stuff broke up.

[jtanguay]

don't forget to dry the inside out.. i've heard of someone hydraulically cracking the block   :shock:

[vwt4]

Cheers guys.

Will do this  

[vwt4]

Just take a used bolt and measure 10 threads with a metric rule...
Use the same old bolt to clean out the threads. In any event don't waste your money with a tap :idea:

It may be a waste of money for a T4 but for some of the engines Ive modded in the past (gasser engines) using ARP studs, ARP recommend using a bottoming tap to clean the threads out.

This ensures the torque reading is accurate.

Maybe I should just use an old bolt on this beastie then!!lol

[Vincent Waldon]

At least twice I've seen people post "oh no don't use a bottoming tap you'll remove metal and weaken the threads... an old headbolt with 4 slots cut in it works best".

I wonder.   Kinda makes sense.. although ARP probably knows a thing or two as well.

Probably 6 of one, half a dozen of the other ?!  :wink:

[vwt4]

At least twice I've seen people post "oh no don't use a bottoming tap you'll remove metal and weaken the threads... an old headbolt with 4 slots cut in it works best".

I wonder.   Kinda makes sense.. although ARP probably knows a thing or two as well.

Probably 6 of one, half a dozen of the other ?!  :wink:

The thing is, if the bottoming tap is the same size as the existing thread, then surely the only thing it should be removing is grime from between the threads?

Where should the 4 slots be cut on the old head bolt? Im guessing bottom middle and top? to allow any crud to escape?

[zukgod1]

Where should the 4 slots be cut on the old head bolt? I'm guessing bottom middle and top? to allow any crud to escape?

I'm picturing 4 groves down the sides of the bolt, top to bottom through the threads.

[Turbinepowered]

^ what he said.

Four grooves along the axis of the bolt would mimic those cut into a tap.

[vwt4]

Where should the 4 slots be cut on the old head bolt? I'm guessing bottom middle and top? to allow any crud to escape?

I'm picturing 4 groves down the sides of the bolt, top to bottom through the threads.

Good point!

It will be a major PITA to do that to a bolt though and still leave the threads in a clean condition so it doesnt damage the thread.
Maybe if I had machining equipment but as it is a bottoming tap seems the answer.
Will post back if it works ok