View Single Post
Old 06-14-2010, 02:53 PM   #1
Ron/IA
Senior Member
 
Join Date: May 2010
Location: Amana IA
Posts: 527
Default Head Bolt Torque-Hot or Cold?

I have been reading with interest the posts of Larry Brumfield and others on cylinder head subjects such as: what compression you run, calculating compression ratio, head and block surface smoothness, etc.

While installing a club member's rebuilt engine a couple of weeks ago; a discussion occurred whether a head's bolts should be torqued hot or cold. There were four of us that day, and our consensus was the engine should be cold; at least that is what we had heard. But, we had to conceed that we had heard the bolts should be torqued with the engine hot too (just not as many times as cold). In other words, none of us really knew for sure which would be best, or why you would pick one way over the other.

Today I read an article written by Murray Fahnestock (1961) stating: "Standard shop practice is to adjust the tension of the cylinder head bolts when the engine is warm." But no where in the article did it say it was the right way. For that matter, Murray didn't actually state what temperature was correct.

If I torqued the head bolts with the engine hot; after shutting it off, getting the torque wrench in hand, and going through the torque sequence could take say - five minutes. The engine will be cooling during that time. Would the head bolt torque vary from the beginning to the end of the sequence? If I torque the head "cold" (usually meaning room temperature), is that meant on a 72-degree day here in Iowa or a 92-degree day in Texas? Would that 20-degree seperation in temperatures make a difference? (Sorry, this is just the way my mind thinks.) Or am I being too critical?

I would be interested in answers to the following question:

1. If you torque your head bolts cold; do you let the engine cool for so many minutes, over-night, or somewhere in between? Why?

2. If you torque your head bolts hot (assume engine operating temperature); do you think as the engine cools the torque is being affected? Why or why not?

3. If you torque your head bolts warm; what do you consider warm? Why do you torque them with engine warm?

In case you were wondering; the above mentioned engine had the head bolts torqued cold when the head was installed, and a re-torque was done warm after the initial start up. The car was then driven 50-miles/day, 8-times, over a 2-week period. The roads used were a combination of long and short flat stretches, hills (mild and steep), and towns. After that period, the head was re-torqued cold. It is now into the second day traveling to French Lick, IN, and as far as I know; all is well.
__________________
Ron/IA
1929 Fordor Steelback

Hawk A Model A Ford Club
http://hawkamodelaclub.org/
Ron/IA is offline   Reply With Quote