1.6TD 77.48mm Piston Service Bulletin Query

[caddywompus]

Has anyone heard of a VW Service Bulletin regarding 1.6 TD blocks that have been bored 1mm (.040") over?  I recently had a friend inform me that the shop were she is having a blown head gasket (1-notch, standard 1.6TD gasket) replaced on her recently rebuilt  (but sadly overheated) 1.6TD with 1mm oversized pistons (77.48mm) refuses to follow the retourque protocol (1/4 turn at 80*C, and another 1/4 turn after 1000km) due to some service bulletin that came up on their computer that stated, TD blocks that have been bored 1mm over need to have the pistons champfered on the top edge 15 degrees to avoid any contact with the head gasket upon retourque.  Now, I've seen a few sets of 1mm oversized 1.6 TD pistons in my day, and I could swear that they already come with a slight champfered leading edge, which would stand to reason if there is a past Service Bulletin already in effect.  

Anyone out there have any comments or pics you could post to clarify this?  One thing is for sure, I think the retourque needs to happen ASAP....

[river_clan]

Did anyone see any 15 degree chamfers on their pistons? Ours didn't appear to have them.....

[fspGTD]

This is the first time I've heard of this recommendation.  If it is true, that is interesting.  I have never had a piston-headgasket interference problem before, but I am not running the max overbore pistons though either.

Chamfering the piston reduces compression ratio by adding volume to the combustion chamber right where you need it least.  Also, if it were not done absolutely repeatably on each piston, you could take more off of one piston than another, making a rough, uneven-running engine.  For those reason if I were in your situation, I would be inclined to do the chamfering very mildly or set up on a machine to make it at least equal to all pistons.  I would first test to see if the head gasket could fit without modifying the pistons, if it were perfectly aligned to the cylinders using dowel pins.  I know these are available to buy for gasser VW engines, maybe they would fit our diesels as well.

Or, if the fit is plain too tight even with the gasket lined up well, if you had a hydraulic head, you could use a 1.9l diesel head gasket that is designed for a larger piston bore instead of a 1.6l head gasket.  With that approach, at least then the volume added to each combustion chamber would be equal between each cylinder.

[josiah47]

Hello,
I have had the 1mm bored done to my engine and have pictures on my site you can see the angle a little bit but they are there, i haven't torqued the head down yet either, just click on my www link and they are there,
hope this help a little,
Bye