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Discussion Starter #1
Hi all,
I was about to put on my freshly rebuilt heads C9OE 302 heads that i got back from my machine shop.
They did a valve job, replaced the valves and put in new valve guide inserts on the exhaust guides.
While cleaning i noticed that on 5 exhaust guides there is a crack in the valve guide boss on the valve cover side.
See picture.
IMG_0600.jpg


I am not entirely sure if these cracks where there before but i think it happened during install of the inserts at the machine shop. IIRC the guides were just cast iron before i took them in. I am pretty sure the machine shop will say it is just fine. Should i be concerned about running it this way?
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I would not be satisfied with the shop if the cracks Were there before or after the guide install. What else didn’t they notice?
 

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Richard, if it were mine, I would ask the shop to replace those valveguides. Sometimes an inexperienced man cracks those while sizing the inserts. LSG
 

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I would want the broken guides replaced. Properly installed, the inserts should have not cracked the guides.
 

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I would not put those heads on. That single pic shows that guide itself has (2) fractures.

Take the heads back to the shop that did the work and point out all of the fractures.

Any experienced engine builder should have picked up on those damages - before or after inserting the guides. Also if those damages where there before they did the inserts, a good shop would have called you and informed you that the heads needed additional work OR that they were not good candidates for a rebuild.
 

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Discussion Starter #6
Thanks all for your replies.
You convinced me to make another trip to the machine shop(when they're back from holiday). I am also afraid that a couple of heat cycles won't do any good since i found that bronze has almost a twice the expansion coefficient as cast iron.

There are 5 exhaust guides that have cracked bosses. I am thinking of having all exhaust guides fully replaced. I heard on a VW forum that certain guides have the tendency to come loose and land on the valve. Do you recommend a specific material or brand/type as replacement guide?
 

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Richard, the thinwall bronze guide is as good as it gets. The problem happens when the worker is in a hurry, or hasn't QUITE learned how to do. I've installed more of those thinwall bronze guides than I can count. What one does to install them is this, 1st, bore the original guide oversized, then blow and bruch it clean. Then, 2nd drive in the bullet nosed bronze insert, 3rd, trim off the excess length of bronze, then 4th, and here is where the problem comes, you use a progression of sizing balls or sticks to force the bronze out and tightly against the inside diameter of the guide. BUT if you do this without a properly sized support on the outside of the original guide tower, it will crack, just like yours have. At the place from which I retired, the valveguide table has a selection of bored out nuts that perfectly fit over the outside of the guides to support them while the guide is sized. If you don't use the supports, guides can crack. What your guys will have to do know is completely bore away the guide, to .500 or .530, and install replacements, and then size those replacements to your valvestems. LSG
 
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