twinc bolt size

[S2Jay]

I agree about the elongation, hence measuring bolt length rather than torque to check rod bolt installation.

I think that there is also another issue of concern. IIRC, the high strength material used for ?Grade 8? type fasteners is indeed much stronger when loaded in tension, but not as strong in shear. Rod cap bolts are [edit] an example where very high strength materials are used for a fastener that is loaded only in tension and does not experience any side force in normal operation. Any applications that could expose such a fastener to high shear load must be avoided in favor of the Grade 5 type [sorry for the U.S. nomenclature]. The harder material of a Grade 8 bolt makes it less flexible & therefore more ?brittle?. It will snap at a lower force if exposed to a load off the longitudinal axis. The relatively ?softer? material of the lower strength hardware provides a greater degree of flexibility, which allows it to absorb a thrust load at some angle off axis. Sorry to drag this even further off topic.

jay
26-5009

Edit:
Ok this edit is just to adjust the ever-so-minor oversight [major error] noted by Rohan [posted below]. My excuse will have to be that it was like really, really late and I was in a bit of a hurry when I wrote the original response. [this is no doubt important only to me].

What I probably meant was that the Connecting Rod itself is constantly cycling through compression & tension loads, the Rod Cap Bolt keeps the cap securely mated to the beam. This is an example of high strength bolt being loaded only in tension with no side forces under normal operating conditions. jay

[vernon.taylor]

Salut

More generally is there a list somewhere of bolt sizes used on the Elan and +2? Apart from Girling servo mounting bolts, I don't need anything in particular but the question arises often.

Merci et @+

Vernon

[rgh0]

Rod cap bolts are a good example where very high strength materials are used and hammered throughout their life in rapidly repeating compression / tension cycles.
jay
26-5009

Hi Jay

Rod bolts actually do not cycle. The design of the join and the bolt is that the rod bolt tension is kept constant and at a high tension load which is why special high strength bolts are needed. As the load changes on the join with the crank cycle the load transfers between the rod join in compression and less compression on the rod join and some transfered to the crank. During this cycle the load on the rod bolt stays the same which is why it does not fail in fatigue. If the rod bolt is not tightened enough it does see some cyclic load and will rapidly fail in fatigue which is why tightening rod bolts by elongation is a good idea especially in race engines rather than torque. Have a look at my avatar !!!!

Bolting is a very complex topic and the right bolt for any particular application is not a simple answer. Carrol Smiths "Nuts , Bolts , Fasteners and Plumbing Handbook" is an essential reference if making changes from standard in this area and a Mechanical Engineering degree helps also.

cheers
Rohan

cheers
Rohan

[Matt Elan]

'Salut

More generally is there a list somewhere of bolt sizes used on the Elan and +2? Apart from Girling servo mounting bolts, I don't need anything in particular but the question arises often.

Merci et @+

Vernon'

For 'standard' fasteners the Parts manual (for the Plus 2) page 9 'Standard Hardware Part Number Coding' gives the code for decyphering type, length, diameter etc for nuts, bolts, screws studs and washers from their part numbers. The system is used on many fasteners on the Elan and Plus 2 but not all (and the 'not all' ones are usually the ones you want of course ) and has been described here before but i can't find the thread.....