Tap an 11mm block out to 12mm, can it be done?

[rabbitman]

Does anybody know if it's possible to drill and tap the head bolt holes in an 11mm block out to 12mm.

[BruceM31]

I'm sure its possible, but a long insert would be required.  Company called time-sert makes good ones.  www.timesert.com Their kits come with all tools needed.  Hope this helps.

[maxfax]

I don't think I'd go the insert route..  Just drill the holes out and re tap them to the bigger size...  With the insert you'd be drilling them out about 2 sizes bigger and taking more metal from the block that is already notorius for cracks..

 I never personally tried it using 12mm bolts..  I have used the inserts to repair the threads back to 11mm..  I suppose that would be not much different than enlarging the hole and just using bigger bolts..  The key would be to do it slow and careful.. Probably best to start the hole with a tapered tap then move to a flat bottomed tap to finish to the bottom..  And lots of oil while cutting..   

The only other thing I've pondered about these earlier blocks is whether they may have used a different alloy than the later ones..  I have nothing to back that thought either way, but it has crossed my mind..  I've seen 11m blocks cracked in all sorts of places (the deck, cylinders, around the main bearings) yet rarely find or hear much about the later ones cracking..

[BruceM31]

Max, I'm in the same boat with you.  Never tried an insert converting an 11 to a 12, but have used and insert to repair an 11 with sucess.  I'd be worried just tapping an 11 hole to a 12.  Lost of room for error ten times over.  Might be easier finding a 12mm block and starting fresh. 

[RabbitJockey]

i'm sure its possible its only .5mm the whole way around the hole, but like everyones saying they already crack with the 11mm hole, i wouldn't want to drill it out, and then tap it any further.

[CRSMP5]

why do you need to??

12mm heads work on 11mm blocks..

drilling 11mm head to 12mm easy peasy..

if its for steach bolts.. gasser 1.8/2.0 8v fit as they 11mm..

[maxfax]

if its for steach bolts.. gasser 1.8/2.0 8v fit as they 11mm..

They fit, and they do thread in a tad further than the stock bolts..  However they don;t have the tensile strength that 12mm stretch bolts, or the standard 11mm bolts have.. 

I'm not saying that the gasser bolts will not work ever, but the failure rate is high..  Almost higher than the rate of the block cracking with the original bolts...

Rabbitman, what exactly are you up to??  Putting a 12mm head on the earlier block??  Attempting an upgrade on an 11mm block? 

[Mark(The Miser)UK]

Are M11 bolts the same thread pitch as  M12? If not then you cannot enlarge to M12, need to be  M13 or M14 with inserts

[clarkrep]

I was going to just tap an 11mm block to 12mm but its not that simple.
As stated, if the pitch isn't the same it won't work.

11mm blocks have M11x1.5 threads

12mm blocks have M12x1.75

I drilled and tapped all 10 in an 11mm block to accept a 12mm helicoil and while it worked I don't recommend it.  

[rabbitman]

Rabbitman, what exactly are you up to??  Putting a 12mm head on the earlier block??  Attempting an upgrade on an 11mm block?  

A guy around here has an 11mm block with some stripped threads and he was askin' me about it.

Blocks are like hens teeth here.

[R.O.R-2.0]

the 12mm blocks have WAY MORE material around the head bolt bosses. someone check it out sometime..

the 12mm block is considerably beefier up top on the deck..

you could tap them for 12mm, but i imagine it would  be no stronger than the 11mm stuff, maybe even weaker since you removed material to tap for 12mm..

[clarkrep]

the 12mm blocks have WAY MORE material around the head bolt bosses. someone check it out sometime..

the 12mm block is considerably beefier up top on the deck..

you could tap them for 12mm, but i imagine it would  be no stronger than the 11mm stuff, maybe even weaker since you removed material to tap for 12mm..

The 12mm blocks do have more material, bosses are cast maybe .75" deeper into the water jacket with a counterbore of sorts that's about .3" deep and a little larger than the major diameter. It would be nice to have exact measurements....I might have it written down at home.

[maxfax]

Rabbitman, what exactly are you up to??  Putting a 12mm head on the earlier block??  Attempting an upgrade on an 11mm block? 

A guy around here has an 11mm block with some stripped threads and he was askin' me about it 'cause I'm the vw diesel guru here .

Blocks are like hens teeth here.

An insert to keep it an 11mm hole would be the best bet, pending which hole it is..  The one by the oil passage is probably the most fragile one from what I've encountered..   It's still gonna be risky due to the factors mentioned above.. A heli-coil would require removing less metal from the block, but isn't as strong as an insert..

[rabbitman]

I think it's the bolts at the bell housing end.

[R.O.R-2.0]

I think it's the bolts at the bell housing end.

definitely the weakest bolts.. those were cracked the worst when i blew the head off my 1.5TD..

have you ever noticed, on the 11mm engines, the bell housing end of the deck, the block is rounded on the corners. its the same shape as the deck. on the 12mm engines, the block is MUCH BEEFIER at the bell housing end, and the block is right angles on the corners, and isnt the EXACT shape of the deck. you can definitely tell that there was alot of material added to the 12mm engines..

the 2 closest to the bell housing, the one next to the oil galley, and a few other random bosses cracked.. 7 out of 10 bosses were cracked!

i think a TIME-SERT would be the best way to fix/strengthen the 11mm blocks..