Connecting rod screw - reuseable?

[Torch]

Just as the title says, are the connecting rod screws reusable?

Says nothing about this in the engine workshop manual, just the procedure of how to re-torque them.

What does pros like Allen do?

[DrDuc]

I have no idea what Aprilia recommends, but I swore off ever reusing them back in my carting days when I tried reusing one and a few miles later had bits of crankcase, connecting rod, and piston sitting in my lap and a huge hole in the crankcase - but that was a looonnngggg time ago and a two-stroke engine.

[cal550b]

yes they are ,

[Torch]

I see your point DrDuc.... but a twostroker with rod screws?

What it all comes down to is how the screw joint is designed. If the screws are not stretched past yield strength during torquing, and past fatigue yield strength during operation, then it should not be necessary to replace the screws. But that's theory. I want to hear what the experienced engine builders in here do.

Thanks cal550!

[Mooseknuckles]

fyi Cal IS an experenced engine builder

[Allen Noland]

yes they are ,

^^^ what he said!

[amauri]

Rod bolt school, good article:
http://www.chevyhiperformance.com/te...nfo/index.html

When I was working on the race team motors I would re-use the bolts one time and then discard.

[Torch]

Thank you all, you're great!

(For easier future forum search, here's the part no for Connecting rod screw AP9150127)

[Danneh]

Still on topic:

What methods do pro's use to torque the rod bolts?

[amauri]

Aprilia service manual calls for the torque angle method described in the article I linked.

The most accurate method is to measure bolt strech, but not possible with a bolt that screws into a blind threaded hole.

[Danneh]

Aprilia service manual calls for the torque angle method described in the article I linked.

Thank you amauri, much appriciated!

As when you first go with the torque wrench to 15Nm then add 48-50 degrees of turning (little more than 1/8 of a full cycle)

Any good way to measure the 48-50 deg?

And where to put "Molicote G-N Plus", in threads or on bearings?

[Torch]

Thank you amauri, much appriciated!

As when you first go with the torque wrench to 15Nm then add 48-50 degrees of turning (little more than 1/8 of a full cycle)

Any good way to measure the 48-50 deg?

And where to put "Molicote G-N Plus", in threads or on bearings?

The only time I've heard of the Molykote G-N product (G-N Plus I have never encountered, and I can't find it on Molykotes website) is in nuclear power plant application, where the clamping force of a torqued screw joint connection is extremely important to control. Surprisingly I have seen results showing bolt stretch (As Amauri writes) as a function of applied torque, with an extreme consistency when using Molykote G-N. And when not using Molykote, the actual bolt stretch has varied hugely at a given bolt torque.

Hence, in a screw connection so important in our engines as the connecting rod screws, I can not enough emphasize the importance of using the recommended Molykote product.

Perhaps you and me (both from Sweden if someone didn't notice) could make a group buy of Molykote G-N Plus since the price is ridiculous. I will contact my friends at the nearest nuclear power plant maintenance department to see if I can get a free sample... I'll let you know, or you've already got it?

In other words, use it on the threads, and on the friction surfaces between the screw and the rod, not on the bearing itself.
.

I suggest you print one of these in suitable size for measuring 49°±1° (and also crank/cam timing etc.):

[Danneh]

Did some googleing on the molykote and came up with

Svenska (för glidlager), swedish (for glide style bearings)
http://www.lundqvist.se/frameset.asp...asp?nr%3D61569

Datasheet:
http://www.devo-tec.de/data/pdf/techinfo_38.pdf

can buy from here in UK it appears:
http://www.univarsc.com/molykote-gn-...lack-1kg-GNPL1

Ahsell (a large swedish distributer) seems to carry it too..
http://np.netpublicator.com/netpubli...n54666425/1034

[Torch]

Did some googleing on the molykote and came up with

Svenska (för glidlager), swedish (for glide style bearings)
http://www.lundqvist.se/frameset.asp...asp?nr%3D61569

Datasheet:
http://www.devo-tec.de/data/pdf/techinfo_38.pdf

can buy from here in UK it appears:
http://www.univarsc.com/molykote-gn-...lack-1kg-GNPL1

Ahsell (a large swedish distributer) seems to carry it too..
http://np.netpublicator.com/netpubli...n54666425/1034

Good, you did your homework better than me. Seems as if molykote on the bearing surfaces wont do any harm, a derivative from it, (Swedish molybdendisulfidfett=MoS2) is often recommended to use when assembling sliding bearings (NOT between bearing and connecting rod, only crank side of bearing). And in our engines where gearbox and engine oil is separated it wont mess up our clutch either, (given we succeed in keeping them
separate...))

Again, main point here is threads and contact surfaces between screw and connecting rod - we want to control screw clamping force (=screw stretch) by measuring torque applied to screw.

[Zicks]

Just did a rebuild of my rxv and used molykote (spelled molicote in manual i think) on conrodscrews bought from ashell in sweden.
Used old conrods and screws had no problems.