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Strange failure on 12v 3.0...

Posted: Wed Jul 11, 2012 3:10 am
by Terafrost
Hi all,

I was just putting the finishing touches on a 3.0 conversion in my GTV6 when I had a small altercation between a couple of pistons and valves! :cry:

I got everything running nicely enough, got 300km on the motor when it started running really rough. I tried to reverse out of my driveway (uphill) and managed to stall it due to how poorly it was running. I turned the key and... Chink!! I jumped out and grabbed my tools, trying to turn it over by hand and it was clearly stuck. Long story short, 2 bent intake valves. Not happy.

Now... Not a drop of oil around the belt tensioner, brand new cam belt, timing spot on.
I was left scratching my head until I managed to knock the distributor/oil pump drive pulley...
The bloody thing was loose! Tried tightening it to no avail and discovered that the keyway had slogged out to nearly double it's original size... F@$!. Checked the cam timing... Nearly 70deg out on the RH head! Thankfully no nasty damage, just the intake valves.

My questions to you:

Has anyone ever heard of this happening?

And does anyone know if the units are interchangeable between the 2.5 and 3.0? The motor I have came from a 75/Milano so they share the same belt profile. I have spares, but I'd rather not pull apart another motor just to find out!

Thanks for listening.

Re: Strange failure on 12v 3.0...

Posted: Fri Jul 13, 2012 3:18 pm
by GarthW
Sorry to hear this mate. I've heard of something similar for sure.

All the best with it and let us know how you go. :wink:

Re: Strange failure on 12v 3.0...

Posted: Sun Jul 22, 2012 7:11 pm
by Greg_Sef
You used a motor from a 75/Milano right? If the auxilliary shaft worm gear was from that car then it shouuld have been OK.

But the gear from a 164 Motronic motor is different. The oil pump turns twice as fast.

But you can't be using that because it won't drive a conventional distributor, right?

I gotta say though I have never seen one of those bushings that the shaft spins in going bad, but I don't doubt it did.


Re: Strange failure on 12v 3.0...

Posted: Mon Jul 23, 2012 5:13 am
by scott.venables
What exactly went wrong? If the auxiliary shaft pulley was loose wouldn't that only affect the ignition timing? Obviously not because you bent some valves, but what happened?


Re: Strange failure on 12v 3.0...

Posted: Mon Jul 23, 2012 6:59 pm
by Terafrost
Motor was from a 75, yes. I used the conventional distributor.

Right - what happened...

Distributor/oil pump drive pulley has two keyways cast into it. One has a locating key/pin (it may have had two at some stage, it all looks pretty worn). It had obviously been loose at some stage, as the keyway in the pulley has slogged out to nearly twice its original size. It was tight when the motor went in. The unit is a much smaller (and clearly weaker) design than the pulley on the 2.5.

The 'locating ring' of the pulley (the inner circle that slips over the actual drive bit) had slogged it to the point where, even when tight, was rotating off-axis. From what I can figure, this was providing the belt with just enough slack on to slip on the camshaft pulley - hence the cam timing being so far out of whack.

I'm having the whole unit replaced with one from a 2.5 as even after playin around at a machine shop, the 3.0 unit still isn't right.

Re: Strange failure on 12v 3.0...

Posted: Tue Jul 24, 2012 11:12 pm
by scott.venables
Wow, that's some serious wear. I would never have thought something like that would happen. Must have been loose for a long time.

Cheers, Scott.

Re: Strange failure on 12v 3.0...

Posted: Thu Jul 26, 2012 12:49 am
by Terafrost
So... Just got back from my mechanic's workshop.
Head was in having shims put in. All went back together fine, until he tried to rotate the camshaft.

Won't turn... Shit.

The head is -for lack of a better term- bent.
Cam journal #3 is sitting proud of the others.


Needless to say I'm not happy.

Anyone is Australia have a RH head to suit a 12v 3.0? Or another f$@#ing motor??