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1975 850 T rear main bearing bolts.

pizza for you

pizza for you

Cruisin' Guzzisti
GT Contributor
Joined
Jun 8, 2015
Messages
176
Location
Ohio
When I was tightening the 25 mm long bolts on the rear main bearing on my 850 T they felt like they may have bottomed out. I tightened them to specified torque of 22 ft lbs but I was getting an uneasy feeling. The main bearing is tight and have all the proper washers installed. Should I have used a 20 mm long bolt instead ?
Bolts
 
I use 25 mm and have never had any issues. 20 will not give a sufficient number of threads engaging. The part number for the bolt is 98054425 - the 25 on the end means 25 mm long.
 
Just checked the depth of the holes and they vary from 22.78 to 23.4 mm. The one bolt was tight and the torque wrench had not clicked. Was worried about braking it. Will try again with a new bolt and go from there. Thanks everyone for your help.
 
You need to add the depth of the hole, the thickness of the main bearing flange, and the thickness of the washer. The flange is at least 8 mm thick, washer another 1+, so a 23 mm deep hole should be plenty deep.
 
You are correct, that's about what I have. I stopped trying to tighten the bolt as I have broken bolts in the past and it felt similar to that. Will use another bolt and go from there.
 
These need to be high-quality graded bolts. Not your generic soft metal 8.8 grade Chinese made Home Depot variety.

You want grade 10.9 and preferably 12.9 grade.
 
note for the future, for you and any others: mcmaster.com is a lovely source for all kinds of fasteners - no reason to compromise :)
 
scottmastrocinque said:
These need to be high-quality graded bolts. Not your generic soft metal 8.8 grade Chinese made Home Depot variety.

You want grade 10.9 and preferably 12.9 grade.
Click to expand...
The factory used 8.8 and in my opinion that's strong enough in this application, if one buys good quality bolts. As tobinh wrote, McMaster-Carr is a good source.
 
You must use your own judgement and different people have different levels of comfort and tolerance.

I myself, prefer to use the “best” parts I can obtain for any job. Especially one that involves major tear down in order to access.

YMMV.

Good Luck.
 
A higher tensile strength bolt requires a higher torque. The torque "stretches" the length of the bolt which locks the bolt and stops it coming undone.
Increasing torque of the bolt means the holes threaded section needs to be able to take the tension. If factory use 8.8 I wouldnt change.
 
Oh God…WTH. Something so innocuous draws all of this fire…

I’m out…this is reaching the ridiculous stage…

Just go ride your bikes Scott. Be happy. Just ride… Stop offering help…. Just ride…
 
Amboman said:
What "fire"? Nobody is allowed to have a differing opinion?
Click to expand...

Of course they can however it’s just reached the ridiculous stage.

My original intent was one of that this repair is not an easily accessible area and that assuming that the OP was not using OEM hardware, that the use of a higher quality steel might be a prudent precaution.

This has morphed considerably.

I personally think that it is over the top. YMMV.
 
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