I did the 5,000 mile service today myself.

Of course, I screwed up one of the derby cover bolts when I removed it (stripped the tork head). It was a dicey day, had to use a bolt remover but was able to get it out.

Anyway, went over to the dealership and of course they're out of zinc replacement bolts (both local dealers are out). I am going to Laconia on Friday, so I ended up buying the chrome bolts that they did have in stock.

However, there are NO chrome bolts for the '06/'07 dynas - only '05 and earlier. Long story short - looked up the specs, and the '06 derby bolts are 1/4-20 and 5/8" long. The previous bolts are also 1/4-20, but either 9/16 or 1/2" long. So the chrome bolts I put in are a little shorter than the stock bolts.

However, as far as I can tell there is plenty of thread catching, and I did put some loctite on them.

So any reason to think there is any problem using the slightly shorter bolts? As far as i would assume, the derby cover has no mechanical stress on it - it is just to prevent oil leaks.

Just wanted to double check other's opinions - because the HD packaging was quite specific as to the year of the bike. Thanks.

 

As a general rule of thumb, if you're threading into aluminum you should have a minimum of 1.5X the fastener's nominal outside diameter worth of thread engagement...if you threading into steel, 1X the fastener's nominal outside diameter.

A 1/4" fastener has a nominal O.D. of .250". Multiply .250" by 1.5 and you get .375" as a minimum thread engagement into aluminum. A 1/4-20 fastener had 20 threads per 1". Divide 1 by 20 and you get a pitch length of .050" (distance between threads). Take your minimum thread engagement of .375" and divide it by the pitch length of .050" and you get the minimum number of turns for a 1/4-20 fastener threading into aluminum.....7.5 turns.

Remember...this is a minimum engagement. Normally 2 to 2.5X worth of engagement is better.

 

hey warren888, I would call that a very temporary fix myself. the application of loctite should help the screws stay attached to the primary case. did you check with your local "ace" hardware store for some chrome replacements or the zinc variety. I would also place an order with your local dealers to get some OEM screws in before you go to Laconia. get some clear fingernail polish and "paint" the inside of those chrome heads on those screws.

 

I always put my torx bit in thehead of screw and give it a five dollar rap with a hammer before I try to loosen it. Havent stripped one yet. And they always come loose nicely. Just dont miss.

 

Warren,
I am no mechanic but I can tell you this. If you run into problems once you are in Laconia. You can always stop in a Merideth HD and get some bolts. It is a good sized dealer, so they should have some. The is also a New dealer in Rodchester NH. (I think on RT11) so you can try there too.

Good Luck!!

 

Thanks for all the input.

A few questions:

a. We are talking about a difference of around 1/16" in terms of bolt length - do you really think that will make a big difference?

b. What is the risk of having less than ideal thread engagement in Aluminum? I am sure there is a strength difference - but given that these are not under any real mechanical stress (that I am aware of), what is the possible failure scenario?

c. I believe the derby cover itself is probably 1/8" thick, and there is a washer (around 1/16") - so about 3/16" worth of thread is wasted. If I put in 9/16" bolts, then there will be 3/8" length of thread engaged, which is exactly 1.5x the bolt diameter. This would just make it in the spec department (thanks Mtnlvr - really interesting to hear the correct specs).

d. If I were to change these - the derby cover has a bolt torque sequence. Given that, can I simply remove one bolt at a time and change it, or will I require a new gasket and re-tork everything from scratch in the correct order?

Appreciate any feedback.

 

you shouldnt need a new gasket and yes you can replace 1 screw at a toime.iv never trqed em ever its just a cover is all. I do tighten em back on sequence like the service manual show.
Far as peeps stripping theses trx screws out part of the problem is you might have a cheap set of bits.on my 96 i cussed them screws a few times.i started things right with the 06 tho picked up a set of lysle bits.Also there is no reson to crank the snot outta the screws for covers.

 

Like you said...it's a derby cover. It's not like it's a head bolt or a chain tensioner bolt. Don't sweat it. Next time your at a shop for something else and you haven't forgotten about this fastener, pick up the original to replace it with.

On a side note, I never used to torque the derby cover screws on my Evo. Then it started to leak. I had to buy a new derby cover as my overtightening warped the cover.