I finally had some time to focus on assembling my 730. I tightened the four studs to 37ft-lbs; went fine. Then went to tighten the four 8mm bolts to 24 lbs. They never got that getting tight feeling. Felt mushy...you know what I mean. Then just as I was ready to pull them back out to check into things, one got tight and clicked the wrench. Cool, I was just being Mr. Worry again. Moved to the next and it snaped about 1/4 turn from where I last left it. WTF? I pulled out the others and the one that clicked was actually streched. The manual says 24 ft lbs and another post here, by who I respect as a good builder, says the same. However, as you probably know, another page in the book has a torque spec for all bolts and it shows 18 ft lbs for 8 MM grade 8.8 bolts. What am I missing. I don't want to buy new bolts and break them off too. I was lucky and got the old one out easy. I'm asking for experience and some sort of input. Thanks. By the way, I had my wrench calibrated before assembly. I've broke or stripped many Rotax bolts in my past and wanted to rule out a bad wrench.

 

Torque should be with clean thread surfaces and one continuous motion (don't wratchet tight torque wrench).

If did that, then find out from vendor and tell us why.

Different instructions sound like need to go to source for backup.
Torques are by bolt size/threads/material and with locktite, shouldn't be problem of backing out.

Recalibrating wrench is extra, so did all you can do.

 

If this motor has been apart before, its possible the bolts were stretched before you removed them when diassembling. If so, the already stretched bolts are not going to tighten to the torque spec. Just always to be sure to tighten the bolts in 2 or 3 steps in a criss-cross patern and to always torque the bigger bolts first then the smaller ones.

 

Torque sequence is important, but most people don't know how to use torque wrench: even those who use them 100's of time per day, like at Sears auto. Everything effects the torque measure, and if someone wrote increased specs from standards, the reason should be explained if possible. Otherwise, I'd go with industry standards if can't explain the variance in specs.

 

[img]i/expressions/face-icon-small-shocked.gif[/img]

 

This motor was only assembled at the factory. I broke it and am now putting it back together. That was my first thought, bolts streched at assembly at factory. But alot of builders on here would have mentioned if that has ever happened before. It has to be me. I'm going to buy new bolts and try again. As a corrective action, I am not going to put grease on the flange. Only on the threads. Maybe the lack of friction on the bolt head caused the over torque. That's all I got.

 

Why are you putting grease on any part of the bolts? I don't see that mentioned anywhere in the book or online.

 

Somewhere it was mentioned to put oil on the threads. I assumed to get a true reading of torque by elimiating friction. I used a small amount of grease to reduce the chance of getting oil between the gasket surfaces. Super **** I know, but that is my life. As for the grease under the bolt head, that was mentioned in an assembly of a Rotax 670 engine. I'm sure this is the problem because no one else here has mentioned having an issue. One thing still concerns me and that is one page says 18 ft lbs and another shows 24.

 

Here is a segment quote from another recent post

"The outer water-jacket bolts must be torqued to 24 ft lbs. Apply oil to these threads also. The cam bolts must be torqued to 37 ft lbs- apply LOCTITE"

I know I saw this in the service book also. I know it says oil and not grease but i realize that might be the issue now.

 

Halfliter,

I know you may have heard of QS9000 or ISO9000, and engineers must find source documentation which is not that difficult with web now.

There are standards for torqueing with bolt material/dia/length/thread, what you're torqueing into, different quantity/kind/size/thickness of washers, etc.. THAT DON"T CHANGE FOR ANYTHING. You just have to interpolate if within boundaries and extrapolate if beyond boundaries. It would be good to know if you have any doubt. I will not get your particular 730 bore, but I will check what mfgr says which in my case will be direct source machinest/metalurgist. Your right about questioning everything and why isn't the typo even addressed after you asked at least once I know. Correlation and consistancy is always a primary crosscheck that should have no loose ends. If it barely torques and breaks while running, ...whoops!

However you do it, it sounds like you need to verify the correct specs somehow. Since they are not critical strength bolts, averages of your best estimates would be better than the bleeding edge of bolt fractures. An engineer would never dismiss your observations, and you seem engineer detailed with the information presented to you: good thing because you will pay when it goes wrong. Feel is always good with torque specs, just go slow and constant. If it don't feel right...? You know already.

Also check for AL flash on bottom and on/in screw holes. That would effect major. AL flash is common and may not have been cleaned completely. ie no sharp edges either on any interface.