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914World.com _ 914World Garage _ head/rocker assy. nuts and a compression Q

Posted by: tat2dphreak Jul 5 2003, 06:06 PM

ok, I'm reassembling the heads onto the engine...

Haynes suggests the nuts that hold the heads be 23ft./lb... I'm starting to question my torque wrench... these things are already VERY tight on the studs and the wrench hasn't clued me in on getting close to 23... my question is this: is it possible to get these nuts too tight? will I damage the heads if I keep going until the torque wrench feels like telling me to stop?

also, how tight should the rocker assy. nuts be? these didn't seem *REALLY* tight when I took them off...

next: according the all-knowing Haynes 120-156 lbs of compression is normal, 100 minimum... I'm assuming this is with the engine cool... how much compression is good when the engine is warm? should it me more? less?

one last Q: how much effect can carbon buildup on the heads have on the compression?... when I removed one head(the 1,2 cyls) there was bad carbon buildup which cleaned up easily... a little B-12 and some elbow grease with a toothbrush easy... this head now looks much better than the one that I was going to put on that side... this side of the engine had good compression when the engine was cool 130/140 but only 60-75 warm... after the cleanup... would it be safe to use this head again? or should I just use the other one?

Posted by: Bleyseng Jul 5 2003, 06:51 PM

Compression is checked with the engine warmed up. If you are getting a worse reading when its hot something is wrong with it. Bad seats or many other things.
Geoff

Posted by: tat2dphreak Jul 5 2003, 07:53 PM

ok... the numbers were from before I tore apart the engine... I'll use the other head.... I could see that I had a burnt valve on the 3,4 side... that head looked terrible... once the carbon was cleaned off the 1,2 side it looked almost new though...

so I should be getting 100+ lbs on a compression test when the engine is hot? am I reading the haynes wrong? I assumed that was the cold compression.

Posted by: Bleyseng Jul 5 2003, 09:40 PM

Hot as in everything is at operating temp. If you don't have 100lbs at temp then something is effin wrong.
How long can you drive when the motor is ice cold? One block maybe...
Geoff

Posted by: thesey914 Jul 6 2003, 01:21 AM

IIRC the rocker assembly nuts (odd 7mm size) should be tourqed to 10 foot pounds. There are values for these in the Haynes manual somewhere.
23 foot pounds is fairly tight but you shouldn't be straining by any means...I reckon either your wrench is duff or maybe you're looking at the wrong scale
Haynes recommends tourqing in stages...-perhaps going to 10Lbs/ft and then 18 lastly the full 23.

Posted by: tat2dphreak Jul 6 2003, 08:41 AM

I think I need a smaller torque wrench to truly torque those... my wrench is a craftsman and starts at 25...

I wasn't straining on the wrench... it just kept tightening more and more... much tighter it seems than what I removed.... one or 2 finally clued me in saying 25lbs... but the others were tight enough as is to make me nervous... my only guess is that either I'm being to cautious or I was wrenching too fast and the wrench missed it's mark... either way I plan to take that head off again today and start again.

I have one more question... the other head I plan to put on has a broken exhaust stud... because of rust and the break, I cannot get 1 nut on... let alone 2 nuts to get the stud out... vise grips just slide around removing the rust... how can I get this stud off?

thanks for the help guys!

Posted by: Dave_Darling Jul 7 2003, 02:17 PM

You very definitely want a wrench that reads the correct torque (23 lb-ft) for the heads. You also want to go in steps. I actually start at 10 lb-ft, go to 15 lb-ft, then add 2 each time. Always use the torqueing pattern (Haynes shows it). I also tap the head with a mallet in between the last couple of torqueings. Not sure if that helps, but I've gotten superstitious about it...

Overtorqueing by a little bit won't hurt things, as the studs have a whole lot more stress placed on them when the engine warms up. Just loosen them again and torque them to the correct values in the right pattern.

The rocker stand nuts are 10 lb-ft, and should be done with that cylinder at TDC or you won't even get the rocker stand all the way down on the head before you hit the torque spec!

You really, really need a torque wrench that reads down to ~9 lb-ft. Even if it's in inch-pounds and you have to convert, it's worthwhile. Remember, the oil sump retatining bolt is torqued to 9.4 lb-ft and it can break your crankcase and cam if you overtorque it!!!

Compression numbers are generally spec'ed when the engine is warm. Cold I would usually expect less. Fresh rebuilds I would also expect lower numbers on, at least until the engine fully breaks in. (Figure a couple hundred miles or more of "break-in" driving.)

--DD

Posted by: tat2dphreak Jul 7 2003, 05:07 PM

thanks for the info Dave!
I picked up another torque wrench yesterday at Harbor freight(goes down to 1 ft. lb) I also have one good for inch-pounds too. I followed the torque pattern religiously... at least I did 1 thing right!

as always Dave... TONS of good info! I didn't realize about the rocker nuts needing to be with the piston at the top....

thanks for all of the help.

Posted by: jkeyzer Jul 7 2003, 06:13 PM

How do you measure compression on an loose engine with no transmission attached?

(Don't say bolt on a loose transmission...)

Posted by: Brad Roberts Jul 7 2003, 06:49 PM

You cant. I have several dummy empty tranny cases and starters I will carry with me to look at a used engine for sale. This will at least give me a "guessestimate cold on what I'm looking at".

I did this with a 3.0 I bought several months ago. Took 15 minutes to bolt a empty tranny and starter to the back of a 3.0.

B