Mistake in the Harley M-8 Repair Manual

[Rmitchell55]

For those of you that have had your motor apart and had put back together there is a mistake in the torquing procedure in the repair manual that if followed will probably result in broken head bolts. A friend of mine that has a small independent shop that works on just about anything has had two oil cooled Harley M-8's in the last couple of months come in leaking oil from the rear head area and on both he has found the head bolt on the rear head by the exhaust port broken. The first bike he repaired by the manual and the customer picked it up and two days later brought it back with the same problem, pulled it apart and found the same bolt broken again. He called S&S and they told him that the manual was wrong and how to correctly torque the head bolts. The second bike he is working on now and I was talking to him today and hew was installing the heads. this bike is a 2019 Street Glide M-8 107 with less that 1000 miles on it and the customer brought it to him leaking oil from the rear cylinder head area. The motor had just been rebuilt and had been sold. The customer had just bought the bike from another person and had no idea what was done to the bike so he also wanted to find out what was in the engine. The cylinders were pretty beaten up so the customer decided to go big,so he is installing as S&S 124 kit on it. It already had a S&S 465 gear driven cam, cam plate and oil pump in it. On page 4-38 of the service manual gives torquing sequence of the head bolt and the last step is to torque it an additional 90 degs. That last step over torques the head bolts and causes the rear one to snap because of heat. S&S says to torque the head bolts to 45 ft- lbs.

 

[Dan SC]

The torque is correct.

If it were the cause of head bolt failures it would have been discovered early on (because a zillion bolts would have failed, and the MoCo would have had to replace them under warranty), but the torque is the same in all model years of the M8 (2017-present).

There was a change made to the service manuals sometime after 2019:

The head bolts are not to be reused.

Use new head bolts and follow the procedure in the manual.

Forget about the torque for S&S, unless you are using S&S head bolts.

 

[ROAD DOG]

I always use the S&S bolts and there torque sequence, Never a problem.

 

[rhino 2]

Any bolt that is subject to high heat should not be reused. You’ll never get the proper torque values…. that was the problem with the early Tri-Glide tie link bolts that would loosen up and people would just re-tighten them, instead of using a new one and preferably an un shouldered bolt..

 

[Dan SC]

Any bolt that is subject to high heat should not be reused.

I have been a Jet Engine mechanic since 1974, and I can tell you that is simply not true.

The service manual will tell you if a fastener can be reused.

In the case of M8 head bolts, the service manual now says not to reuse them.

 

[rhino 2]

I have been a Jet Engine mechanic since 1974, and I can tell you that is simply not true.

The service manual will tell you if a fastener can be reused.

In the case of M8 head bolts, the service manual now says not to reuse them.

I knew that long before Harley figured that out.....And we are talking about Motorcycles here ...So 'I' Me not being familiar with jet engines ill have to agree with you on jet engines..

 

[Dan SC]

I knew that long before Harley figured that out.....And we are talking about Motorcycles here ...So 'I' Me not being familiar with jet engines ill have to agree with you on jet engines..

The point is to follow the service manual.

There are many fasteners that are used in high heat locations on Harley Davidsons that are reusable.

 

[Jack Klarich]

I have been a Jet Engine mechanic since 1974, and I can tell you that is simply not true.

The service manual will tell you if a fastener can be reused.

In the case of M8 head bolts, the service manual now says not to reuse them.

It has been an ongoing thing since Evo days to refer to the manual and TSB on reuse of head bolts, even TC engines had similar warnings and TSB concerning this problem

Torque to yield fasteners are here to stay and are more critical to follow the manufacturer guidelines be especially careful to clean mating threads and also #1 to lube or not and where to lube( IE the head surface of head bolts, not the threads)

 

[Dan SC]

It has been an ongoing thing since Evo days to refer to the manual and TSB on reuse of head bolts, even TC engines had similar warnings and TSB concerning this problem

Torque to yield fasteners are here to stay and are more critical to follow the manufacturer guidelines be especially careful to clean mating threads and also #1 to lube or not and where to lube( IE the head surface of head bolts, not the threads)

Keep in mind, just because a fastener is torqued and degreed does not mean it is a torque to yield fastener.

The latest (2016) service manuals for the TC models do not designate the head bolts as one time use.

The issues with Evo engines was not the head bolts, but the cylinder studs.

There are very few reports of broken M8 head bolts on any of the Harley forums, in fact, Fuel Moto was reusing M8 head bolts for years without issues before the factory determined the bolts were one time use.

When I recently assembled the M8 engine in my 2019 Electra Glide Standard, I followed the manual (2019) and reused the bolts, I have had no issues.

If the heads ever come off again, I will follow the latest manual which says toss the old head bolts into the scrap pile.

 

[Jack Klarich]

Keep in mind, just because a fastener is torqued and degreed does not mean it is a torque to yield fastener.

The latest (2016) service manuals for the TC models do not designate the head bolts as one time use.

The issues with Evo engines was not the head bolts, but the cylinder studs.

There are very few reports of broken M8 head bolts on any of the Harley forums, in fact, Fuel Moto was reusing M8 head bolts for years without issues before the factory determined the bolts were one time use.

When I recently assembled the M8 engine in my 2019 Electra Glide Standard, I followed the manual (2019) and reused the bolts, I have had no issues.

View attachment 113500

View attachment 113501

Evo engines had head bolts ( nuts) with CP stamped on the head that Harley replaced with a newer model because of stretching threads, that said it is important to always check the cylinder studs torque before reassembling a fresh top end

 

[JTJersey]

I miss my Panhead days. Torque the bolts? Get them as tight as you can then hit the wrench with a hammer a few times. Go riding.

 

[Rmitchell55]

Talked to the shop today and found out more info on the head bolt issue, it is not the studs that are breaking it is the nuts that are breaking at the washer face. The sidewall of the nuts are really thin, so it doesn't take much over torquing then to get them to crack. From talking to S&S that last 90 degs. of torque according to the repair manual takes the torque value to over 70 ft-lbs where-as the torque value should be 45 ft-lbs. The first M-8 bike that my friend rebuilt he used all new Harley studs and new Harley nuts and used the Harley procedure. He Dynoed the bike and sent it out with the owner, and two days and 200 miles later the guy brought it back with the same problem, the right rear nut on the rear cyclinder snapped off at the washer face.

 

[Dan SC]

Talked to the shop today and found out more info on the head bolt issue, it is not the studs that are breaking it is the nuts that are breaking at the washer face. The sidewall of the nuts are really thin, so it doesn't take much over torquing then to get them to crack. From talking to S&S that last 90 degs. of torque according to the repair manual takes the torque value to over 70 ft-lbs where-as the torque value should be 45 ft-lbs. The first M-8 bike that my friend rebuilt he used all new Harley studs and new Harley nuts and used the Harley procedure. He Dynoed the bike and sent it out with the owner, and two days and 200 miles later the guy brought it back with the same problem, the right rear nut on the rear cyclinder snapped off at the washer face.

Amazing, the M8 engine has been out since 2017, if the problem were widespread, it would be all over the tech forums (even small problems look like major catastrophes on the internet).

Again, what S&S says is irrelevant, they are using different parts than Harley.

Just because one mechanic has a theory that the torque is incorrect does not make it so, especially since he has had repeat problems...

Something else is going on there...

The torque in the manual is correct, or we would be reading about a zillion head bolt failures.

 

[Dan SC]

Evo engines had head bolts ( nuts) with CP stamped on the head that Harley replaced with a newer model because of stretching threads, that said it is important to always check the cylinder studs torque before reassembling a fresh top end

I have been lucky with head bolts and studs on my Evo, it still has the oem parts from 1989, not one stud has come loose or pulled out, so far...