Bama Rides Forum

Open House => Tech Talk => Topic started by: bblass on May 12, 2016, 07:52:33 AM

Title: Re-torque bolts 24 hours later?
Post by: bblass on May 12, 2016, 07:52:33 AM
So last night I finally cranked that CB750 that I've been working on the past year and a half only to discover it's weeping oil from the head gasket. When searching the forums I discover this is a common thing and that the trick to avoiding it is to torque the head bolts in order, wait 24 hours and then come back and torque them again.

I've never heard of doing this before and neither of the manuals I used made any mention of it. Is this some sort of secret technique people wait for you to learn the hard way? I 3-step torqued all bolts to spec and used a multi layered steel gasket and sealant.

Do you think re-tightening the head bolts will solve the issue and spare the gasket or should I just go ahead and do the head up over again?

It was a wonderful feeling when she cranked, but less so when I saw the puddle of oil.
Title: Re: Re-torque bolts 24 hours later?
Post by: jrobinson on May 12, 2016, 08:32:27 AM
I don't remember ever needed to be re torqued 24 hours later on any kind of engine, but that sounds cheaper than replacing the gaskets.
Title: Re: Re-torque bolts 24 hours later?
Post by: norton73 on May 12, 2016, 08:56:59 AM
I've never heard of retorqueing 24 hours later. It is common to retorque after a heat cycle,  ie,  running it for a few minutes,  letting it cool then retorquing.
but usually Japanese bikes don't require that.
Title: Re: Re-torque bolts 24 hours later?
Post by: lk2rd on May 12, 2016, 10:34:23 AM
I'd definitely give it a shot.  I have had to retorque valve covers soon after installing new gaskets. BTW, did you check the head for warping before reassembling? I had a slightly warped head on a four cylinder car back in the day. Everybody I talked to about it said it had to be replaced or resurfaced.  It was an overhead cam and resurfacing would have probably made line boring and sleaving the cam towers  necessary.  I just took a chance on using the head as it was.  That head did require retorquing maybe three times before it finally settled.  That motor ran fine for at least a couple more years and was still OK when I got rid of it.
Title: Re: Re-torque bolts 24 hours later?
Post by: bblass on May 12, 2016, 01:30:25 PM
I didn't have it decked or checked for warping but that could definitely be one of the issues. I plan to go a couple of lbs above spec this time and see if that helps any.
Title: Re: Re-torque bolts 24 hours later?
Post by: Yankee Dog on May 12, 2016, 03:58:03 PM
I am not much of a mechanic but over torqued plumbing is a bad thing.  I wouldn't imagine engines are any different.  I did work in an engine plant a while back.  Torquing something twice was not done.  You don't get the same results.   Yes. The force required is the same but the pulling force is different
Title: Re: Re-torque bolts 24 hours later?
Post by: bblass on May 12, 2016, 04:41:03 PM
Damn... It's starting to sound like the fixing the issue means replacing the studs.

If the bolts are torqued properly when the head is removed then the only answers could be bad gasket (which should be readily apparent) or that the studs holding the jugs and head to the block have stretched.

I'll post a follow up with pictures.
Title: Re: Re-torque bolts 24 hours later?
Post by: kdtrull on May 12, 2016, 08:11:49 PM
Where I work, applying torque to a fastener that has already been torqued is forbidden.  However, breaking torque then re-applying torque is accepted.
Aside from that, I'd be tempted to bend the rules any number of ways before I pulled the head off again.  Good luck....whatever you decide.
Title: Re: Re-torque bolts 24 hours later?
Post by: griff on June 03, 2016, 07:29:08 PM
Do you know your torque wrench is any good? When was the last time it was calibrated?
Title: Re: Re-torque bolts 24 hours later?
Post by: bblass on June 03, 2016, 08:59:17 PM
Do you know your torque wrench is any good? When was the last time it was calibrated?
It's been a bit, but I have checked them against a few other wrenches and they're all pretty close to one another. Think I may have finally fixed it by using a bit of copper gasket sealant.
Title: Re: Re-torque bolts 24 hours later?
Post by: WECSOG on June 03, 2016, 09:27:35 PM
That used to be standard procedure on any engine assembly. Run it a bit, then break torque and re-torque on each head bolt or stud, one at a time.
Title: Re: Re-torque bolts 24 hours later?
Post by: bblass on June 03, 2016, 09:30:57 PM
That used to be standard procedure on any engine assembly. Run it a bit, then break torque and re-torque on each head bolt or stud, one at a time.
This time around I was much more careful. Used copper gasket sealant, 3 step torqued and then came back and checked them again the next day. Good news is, no leaks!
Title: Re: Re-torque bolts 24 hours later?
Post by: Nice Goat on June 03, 2016, 10:26:18 PM
"bolt relaxation"...