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Head cracking a common problem?
https://slantsix.org/forum/viewtopic.php?t=45263		 Page 1 of 5
Author:  green1970 [ Thu Jun 09, 2011 10:02 am ]
Post subject:  Head cracking a common problem?
I haven't posted on here in about 2 years. Sold my 70 Valiant and just yesterday found a nice 71 dart with a 3 on the tree so I scooped her up. Driving her home my wife said it smoked some and under further investigation decided to pull the head today. The gasket was blown, bad. The temp gauge wasn't working on the 35 min trip home so I don't know what she was running at. I took the head to a reputable head shop here in town and they are gonna pressure test it and what knot to make sure there are no cracks, I just wanted to ask if they are common to cracking? They quoted me 85 to clean, check and mill the head but 220 to fix it if it's cracked.
Author:  Joshie225 [ Thu Jun 09, 2011 10:06 am ]
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Cracking a slant six head is rare.
Author:  green1970 [ Thu Jun 09, 2011 10:24 am ]
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Sweet. I really didn't want to shell out 300 bucks right now. It had plenty of power just smoky. The guy at the shop kinda scared me with his reaction to seeing it and how white the valves were. Thank you for the quick reply.
Author:  Joshie225 [ Thu Jun 09, 2011 10:36 am ]
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I'm sure you're going to fix the temperature gauge and whatever is wrong with the cooling system, but make sure you do a good valve adjustment as well.
Author:  green1970 [ Thu Jun 09, 2011 12:57 pm ]
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Supposedly this car only has 26000 miles on it. I kinda believe it because most of the car is in great shape but blown head gasket? I don't know. I will get the gauge working and also adjust the valves and do an oil change and whatever else it may need before I start driving her.
Author:  green1970 [ Fri Jun 10, 2011 10:13 am ]
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So, the machine shop called a few hours ago and said that they cleaned the head up and compression checked it and it needs a valve job. Said it is 85 bucks for the valve job plus whatever parts cost. Since this isn't going to be a 100 buck job any more think I should get the head milled any? Any suggestions as to how much. I'm not looking for a race car but since the head is off and there and the bill is growing I figure why not.
Author:  Doc [ Fri Jun 10, 2011 10:23 am ]
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Seeing that the head is currently off the engine, measure how far down the piston is, when set at TDC and give us that number.
DD
Author:  WagonsRcool [ Fri Jun 10, 2011 10:43 am ]
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Since many slants had pistons that were .140-160" down the hole at TDC, sub 8:1 compression ratios were the norm. So if you can bring it up a half point more, then great. Check you shop's rate for head cuts. Some will charge more past a certain depth of cut (it can take more than one pass depending on the cutting machine).

That being said, IMO if you go more than 0.020-.030" you can exceed the rocker adjusting screws' useful range & can have problems unless you get shorter pushrods &/or you check & adjust rocker to valve geometry as needed. Shimming the rocker shaft MIGHT work, it might not.
Author:  green1970 [ Fri Jun 10, 2011 11:44 am ]
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I will try to take the measurement this evening. About how long does it take to do a valve job anyway? I wouldn't really want to go more than .01 I don't think.
Author:  bigslant6fan [ Fri Jun 10, 2011 5:35 pm ]
Post subject:  .
Just milled one 0.050 and used a NOS head gasket, plenty of valve adjustment left. The S/6 has a very thck deck surface,many racers have milled them 0.100 or more with out problems.
Author:  green1970 [ Fri Jun 10, 2011 6:18 pm ]
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Sweet action. Is that your engine in your sig? I just measured the depth with my hinky old gauge and got .140-ish. maybe .142 but I'm sure that is just my crappy old gauge. I called the shop a little bit ago and they said they would have me a price monday morning. My Felpro head gasket kit came with valve guide seals. Should I give them to the shop and let them use them or is the Felpro stuff good quality? The head gasket is bent pretty good :x What all do they do during a valve job? Do they actually replace valves or just resurface them? I have never had any head work done as you can probably tell.
Author:  Joshie225 [ Fri Jun 10, 2011 7:22 pm ]
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A "valve job" should include hot tanking the head, checking the valve spring tension, checking the valve to guide clearance, resurfacing the valve seats and valve faces and new valve stem seals. Anything extra like surfacing the head or valve guides will be extra. If the engine really does have only 26k miles the guides should be alright, but might not be. The FelPro valve stem seals are good so take them to the machine shop. The FelPro head gasket is also good, but it's thicker than the stock one so you have to mill the head about .020" just to have the compression ratio you did with the steel shim gasket. I had to mill a head .080" (ended up at 50cc) just to get a true 8.5:1 compression ratio. I was still able to use stock length pushrods.
Author:  sandy in BC [ Fri Jun 10, 2011 8:19 pm ]
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Quote:
That being said, IMO if you go more than 0.020-.030" you can exceed the rocker adjusting screws' useful range & can have problems unless you get shorter pushrods &/or you check & adjust rocker to valve geometry as needed. Shimming the rocker shaft MIGHT work, it might not.

NO.....you can cut a lot more than that before needing shorter pushrods.
I have milled .080 and got away with stock pushrods. ,,,,at .140 I had to call Smith Bros....
Author:  green1970 [ Fri Jun 10, 2011 8:30 pm ]
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So what should I tell them monday? Mill .080 since I have the felpro gasket? I sure don't want to do away with any of the compression. How would I know if I need shorter pushrods? If I do need them where can I get em and about how much do they run?
Author:  65CrewCabPW [ Fri Jun 10, 2011 9:30 pm ]
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Quote:

That being said, IMO if you go more than 0.020-.030" you can exceed the rocker adjusting screws' useful range & can have problems unless you get shorter pushrods &/or you check & adjust rocker to valve geometry as needed. Shimming the rocker shaft MIGHT work, it might not.
I whacked .165 off my head and still have PLENTY of adjustment left on the rockers. Don't spread this around, please.
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