Loose head bolt

Towner · Jul 3, 2013

Hello,

after a exhaust thread repair, I retorqued the head of my 850 Commando for the third time (first time after 20 mls). All bolts turned a bit, but the front bolt on the right side was relatively loose. It needed nearly one turn. I already recognized that at the last time. Can it be a sign of material weakness ? Should I renew all the bolts ?

Regards
Ralf

Guido · Jul 3, 2013

It could be a sign of a pulled thread. Are you talking about one of the head bolts near the spark plugs or one of the stubs in the head.
The head studs threads are more likely to be pulled than ones screwed in the barrels.
Remove the bolt that has become loose and inspect the threads for material.

Towner · Jul 3, 2013

Guido said:
It could be a sign of a pulled thread. Are you talking about one of the head bolts near the spark plugs or one of the stubs in the head.
The head studs threads are more likely to be pulled than ones screwed in the barrels.
Remove the bolt that has become loose and inspect the threads for material.

I mean the bolts near to the spark plugs. They are made of steel, even like the threads in the barrels. I just ordered 4 new bolts. They seem not to be the first bolts. May be the PO changed them and the quality is not ok. The threads in the barrels can usually not be the cause. The bolt can be torqued without a problem. But I will renew the 4 bolts and check it after another 300 mls.

Ralf

ML · Jul 3, 2013

I suggest as a pre-caution you should check the length of the new head bolts with the depth of the holes from the head through to the barrel. If a bolt is too long it will bottom out and the torque reading is false, it is not actually pulling the head down.

ILLF8ED · Jul 3, 2013

Towner said:
Hello,

after a exhaust thread repair, I retorqued the head of my 850 Commando for the third time (first time after 20 mls). All bolts turned a bit, but the front bolt on the right side was relatively loose. It needed nearly one turn. I already recognized that at the last time. Can it be a sign of material weakness ? Should I renew all the bolts ?

Regards
Ralf

What is it with the right front. That's the one that stripped on my 750 head last year. It pulled the helicoil that was there. Phil Radford had to put an insert in. All is well now.

Nater_Potater · Jul 4, 2013

illf8ed said:
What is it with the right front. That's the one that stripped on my 750 head last year. It pulled the helicoil that was there. Phil Radford had to put an insert in. All is well now.

I'm guessing it's the left bolt that strips on our brother's engines in the southern hemisphere... :roll:

Towner · Jul 4, 2013

ML said:
I suggest as a pre-caution you should check the length of the new head bolts with the depth of the holes from the head through to the barrel. If a bolt is too long it will bottom out and the torque reading is false, it is not actually pulling the head down.

Thanks for the tip ! I will check that. But I get the original AN bolts - suppose they would be ok.
I applied some oil on the threads before mounting. That maybe a reason as well. I'll clean them before mounting the new ones.

concours · Jul 4, 2013

Towner said:
ML said:

I suggest as a pre-caution you should check the length of the new head bolts with the depth of the holes from the head through to the barrel. If a bolt is too long it will bottom out and the torque reading is false, it is not actually pulling the head down.

Click to expand...

Thanks for the tip ! I will check that. But I get the original AN bolts - suppose they would be ok.
I applied some oil on the threads before mounting. That maybe a reason as well. I'll clean them before mounting the new ones.

Oiled threads are correct. Not TOO much, eh? like partially filled the blind hole? (Hydraulic lock leaking down slowly)

Towner · Jul 4, 2013

concours said:
Oiled threads are correct. Not TOO much, eh? like partially filled the blind hole? (Hydraulic lock leaking down slowly)

Maybe, but it was the first time I applied oil and without oil I never had any problems.

CanukNortonNut · Jul 5, 2013

Towner said:
ML said:

I suggest as a pre-caution you should check the length of the new head bolts with the depth of the holes from the head through to the barrel. If a bolt is too long it will bottom out and the torque reading is false, it is not actually pulling the head down.

Click to expand...

Thanks for the tip ! I will check that. But I get the original AN bolts - suppose they would be ok.
I applied some oil on the threads before mounting. That maybe a reason as well. I'll clean them before mounting the new ones.

Towner
Did you replace the washers under these bolts? Or the P.O.? The washers for the head bolts beside the sparkplugs need to be extra thick. This might be causing your bolts to bottom out.
Regards,
Thomas
CNN

pete.v · Jul 5, 2013

CanukNortonNut said:
Towner said:

ML said:

I suggest as a pre-caution you should check the length of the new head bolts with the depth of the holes from the head through to the barrel. If a bolt is too long it will bottom out and the torque reading is false, it is not actually pulling the head down.

Click to expand...

Thanks for the tip ! I will check that. But I get the original AN bolts - suppose they would be ok.
I applied some oil on the threads before mounting. That maybe a reason as well. I'll clean them before mounting the new ones.

Click to expand...

Towner
Did you replace the washers under these bolts? Or the P.O.? The washers for the head bolts beside the sparkplugs need to be extra thick. This might be causing your bolts to bottom out.
Regards,
Thomas
CNN

I sure agree with this. Without those thick machine washers, those bolts will suck right into the soft head. Although you surely do not want to bottom out, you do want to utilize all the threads you have.

Towner · Jul 7, 2013

Thanks all for your hints. It was not the first time I removed the head and last time everything worked fine with the same bolts and washers. The only difference was that I oiled the threads this time. Meanwhile I fitted new bolts with the old washers. The washers are thick and the new new (original AN) bolts have the same lenght as the old bolts. So I think, it is no bottom out problem. The loose bolt was more wet than the others, so it could have been the reason. Is it recommended to change the washers everytime? Ok the washers can wear out a bit, but do you think that that could be so much, that the bolts can bottom out ?

Edit: With other words: Is the space between bolt and bottom such close, that a worn washer could cause that the bolt bottom out ???

Ralf

Towner · Jul 8, 2013

Just ordered new washers. I will change them and measure it.

Towner · Jul 12, 2013

Now I replaced the washers and measured the holes. There is about 1cm space left at the bottom. So it is definately no bottom out issue.

Ralf

Loose head bolt

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