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Old November 6th, 2019, 11:07   #5
Franko6
 
Join Date: May 2005
Location: Sw Missouri
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As I said, I am not familiar with the twin cam PD's, but the nut and the tensioner for the rest of the PD's and virtually every other belt driven TDI Might SAY they are TTY, but I don't think so.

Just like the engine mount bolts, that are supposed to be TTY, they are actually 10.8 bolts, which are 1) not that hard and 2) only stretch from intentional abuse...+1/4 turn. We never liked the business of the preload +1/4 turn. That is actually a manufacturing thing, for their convenience, not yours. I have a torque wrench and use it.

The point being, unless the setup is entirely different for the tensioner, it's really not a TTY bolt or nut. I think the threads for the tensioner stud is 8 x 1.25- 12 x 1.5. The threads for the PD and Common Rail are threaded to the end. I never figured why they do that, but it might be that it does stretch. The way to check is to lay the old stud threads end to end into the new stud. If the threads won't match up, it stretched.

Now, about the installation of the guides:

Bronze guides are finicky. When installed the guide will compress on the O.D. and close up the I.D. It's not just that driving them will cause a distortion, it's the physics of the material. We intentionally make our guides slightly large on the I.D., and have a very close tolerance on the O.D. It must press in, but carefully.

I will not soon forget when Febi stopped using S. Africa and switched to China for guides. Our employee, who had done hundreds of cylinder heads, shoved guides in just like he always did... Broke 5 Cylinder heads... We gave away a lot of heads that week; new ones. And made sure that never happened again. We started making our own guides.

So, measure close, freeze the guides and heat the head. They go in easier that way.

As for seats, you cannot trust that the new guide is going to align the valve to the exact same seating. It's not going to happen. Sure, you can lap, which is time-consuming and even then, the valve projection will not be equal. Setting valve height, then cutting the head gasket surface for proper projection is the order of business. Then, finally, trim valve stems, so you do not take up all the clearance in your cam followers. There is a measureable amount of preload for hydraulic lifters.

Those are the rules. You don't have to follow them. But quality is it's own reward.

Finally, why we always surface a cylinder head:

You are holding back 19:1 compression ratio. Under the best of situations, it will still want to leak. Flat is flat. Proper projection of valves means even running engine. What is more, the head tends to heat warp length-wise, but the block warps into a valley, with the webs between the cylinders as the low point. To check the block, lay a machinist's block (we use a 6" x 1" x1/2", on edge, across the head from head bolt to head bolt,in line with the webs between cylinders 1-2, 2-3 and 3-4. Shine a bright light behind the machinist's block. If you see daylight, you have a block that has warped into a valley. Daylight under that point is where the head gasket will likely blow.

You can also see the distortion of the block by dragging a single cut bastard file across the block's head gasket surface. People tend to think cast iron is solid. It's not... it is somewhat plastic and the head bolts will pull the sides of the block UP.

Some people think when it comes to head work I have OCD... actually it's CDO... I have to alphabetize it...
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