Loose head bolts (very strange).

[TADracer]

Anyone ever have this happen?

I had the motor out of the frame and the head and jugs off back in 2009. I assembled everything back and torqued the head bolts in stages to the specification and after riding a few hundred miles re-torqued them again to specification (they had not changed). I check this every spring during my yearly major tune-up and they have always been on specification however I never did the tune up this year (I know, shame on me).

Recently I noticed a bit of oil between the cooling fins where the head meets the top of the cylinders on both sides. Also there was a small trail that ran through the head and down into the valley where the #3 plug is. I figured the cam chain tensioner but it is sealed up and dry. After looking all over with a flashlight I noticed a wet area at the base of the cylinders at the front of the motor and oil trails leading up the motor caused by wind.

I know I had sealed this area well when I had the motor apart as it has never leaked until now. I figured I could pull the head and lift the cylinders a bit to get something in there to seal off again so I started to loosen the acorn head nuts. They were all at only 5 Lb/Ft consistently. When I discovered this I re-torqued them to specification, cleaned the motor off and the oil leak has stopped.

I am stumped as the head bolts have remained tight for several years and now they all loosen to 5 Lb/Ft consistently? Has anyone else had such a thing happen? Does anyone else care to venture a guess at a cause?

Thanks cause I am stumped on this one.

[ViperRon]

Seen it and not just on this bike. I check the torque on them on tune up and when I resync some times there is one or two loose sometimes not.

[GLoweVA]

Seen it too, but with bad consequences.
On my SG, they got so loose that there was blow by past the head gasket and that caused a loss of power on those 2 cylinders and when I tried to limp her home on 2, I burnt a hole in the pistons of the 2 that had compression.
(2 errors here: 1. should have paid attention to the symptoms, 2. not rode her home)
Of course, all this is hindsight and if I had to do it over again, I'd have the wife come get me and had the bike towed home. (the tow bill would have been less than the engine fix)

My first symptoms that I had a problem was as I was crusing down the slab, I looked down at the #4 outside forward nut and saw it actually spinning due to engine vibration. I pulled over and put a wrench on it and finished riding to work and got there and tightened it again. Then once again after I got home that afternoon. The next morning on the way to work is when it went to hell in a handbasket.
Looking at the head gasket, I think it failed first and the exhaust gas blow-by was what was vibrating/heating the stud and this caused the nut(s) to come loose.

Your situation may be different, but I think it's good to share all similar experiences so that others may learn and it may even prevent some failures.

[trbig]

Only thing I can think of is that when you innitially put it together, then ran the motor, then torqued them again, at some point your engine got much hotter than it did during this innitial "Squishing" of the head gasket. So the extra heat would expand the metal, squishing the head gasket even more, resulting in looser head nuts when it cooled.

Just a guess though.

[GLoweVA]

Yeah, those head gaskets are only good to get squished so many times and they'll give up after that.

[trbig]

Yeah, those head gaskets are only good to get squished so many times and they'll give up after that.

Never experienced that. As a matter of fact, I re-use them over and over as long as they haven't de-laminated and the steel combustion rings are in good shape. My thinking is that they can only be squished so far.. then can't be squished any further and you're good to go. I've been re-using head gaskets on bikes since I was a kid and never had a failure there... knocking on wood.

[TopCatGr58]

Hey Mike,

You and Tod are much more experienced and knowledgeable mechanics than I. One theory....did you use a touch of oil on the head nuts before you torqued them? If not, then you may not have actually achieved the full amount of torque....bolt stretching due to the frictional resistance with a lack of oil? And then just heat/vibration allowed the nut(s) to eventually work loose. My understanding of the torquing process is putting a STRETCH tension on the headbolt that the nut is being tightened onto. Heat causes the metals to stretch and if not enough torque was applied, then it might stretch enough to relax the torque/tension of the nut which can then allow it/them to vibrate loose???

I wonder if going an extra 5 lbs above the stated value would hurt anything??? 25 lbs seems rather low compared to other car engines head bolts I've installed over the years!

T.C.

[trbig]

That is a good point, TC. The book does say to use oil when torquing those. Maybe the oil then bakes the nut in place? lol..

I've often wondered why some people have things routinely go wrong with these bikes, while others never have a problem. Many people never have a 1st/2nd gear problem.. ever. Those people make me sick. lol..

[IanDMacDonald]

Ughhh. One more thing for me to worry about.

[TADracer]

Yep, I did use a touch of oil on the threads when I assembled the motor back in 2009. Threads on the studs and inside of the acorn nuts was clean too. I always do this because a long time ago a well known drag racer told me a lot about torqueing things and I rarely have a fastener failure or anything come loose. That's why I use a torque wrench on most everything.

In fact, when I re-tightened the acorn nuts this time they still turned very smoothly until the click of the wrench. I did tighten them down to 28 Lb/Ft this time though. So now I am wondering if the age of the studs might have something to do with it. After all, they are kind of long and over 30 years old. Awhile back I was thinking of contacting ARP to see what it would take to have a set of studs made up for the XS motor with the idea some of us might like to change out the old studs.

Well actually I am glad to see some of you have seen and experienced this before. I guess I am lucky since it appears I have no damage at all from this other than a few baked on oil stains. I will start checking head bolts more often.