Boxerworks.com

Hi Boxerworkers!
New to the Forum.

1983 R45. Fairly new to me. I've only done 500km on it.

The bike starts vibing and rattling a bit around 5000 RPM. I was already planning on doing a valve check and adjust later this coming week, but my father (a more experienced mechanic than myself) suggested I make sure that the valve springs are not weak, and ask around if the R45 or airheads in general are prone to weak valve spring issues.

Do airheads tend to have weak valve spring issues?

Is it more likely just a valve out of spec?

Thanks!

You didn't tell us what is the total mileage. Go through the usual maintenance routine first, as suggested, then start looking for oddball things. The R65 wasn't a well regarded bike, as it didn't come close to equaling the larger twins.

I would expect a check of a parts catalog will show that it uses the same valve springs as the R65. I don't know their history of life length.

Do you get a loss of power, or flattening of power when it starts to vibrate at 5 k rpm?

I've been on the R65.org forum for 8 years and I don't recall weak valve spring ever been mentioned as problem

Some vibration is typical of an R45/R65 around 5000 RPM but I wouldn't remotely describe it as a rattle. My R45 is turbine smooth up to 5000 and then starts to buzz a little but it's not something that bothers me. Once you are satisfied that the engine is tuned and balanced as well as it can be, then engine mounts are worth checking for torque settings.

Some say that experimentation with the engine mount torque settings can reduce vibration a little or move it up the rev range. I found that using the lower 1985 model R65 torque settings helped mine. But the thing that smoothed my engine out the most was sorting out the float levels in the carbs. My big insight was to realise that unless the floats are new or they are known to both weigh the same then the usual methods of setting float levels are invalid and may produce unequal operational fuel levels.

If everything else fails there used to be after market rubber engine spacers available. A search on R65.org will produce some information on them..

Thanks for the thoughts, Gents! It is much appreciated. I will post again after I get back to my bike and figure it out.

Duane, She has about 58,000km (36,000mi). It does seem to flatten out power wise, a bit. In 5th gear it is especially noticeable. I don't think I have gone over about 90km/h and that felt like I was pushing it too hard to stay that high for very long. Trying to be gentle until I get to know all her idiosyncrasies. Yes, I know it is a 27bhp machine, and no, I don't expect it to be a 1200GS Autobahn beast. But I should be able to get a little more out of her.

I have an appointment at BMW next week for some new rubber, so if I haven't figured it out until then, I will ask the guys there what they think. Hopefully they are cool

Cheers, Lads!

Power wise even the 27 HP model should cruise comfortably at more than 90KPH but with a 4.25 final drive I guess you are very close to the vibration period at 5000RPM or approx.100 KPH. If you push through it the engine should smooth out again at higher revs. These engines will spin safely at 6000 RPM all day long.

One option might be to change the final drive to the 3.89 fitted to the 35HP model. You would also need a speedo with a 1441 ratio to match.

Thanks Barry! That is an interesting idea with the 3.89 final drive. I may look into doing that if I can do it without spending a lot. Trying not to put too much money into this bike.

Thanks for the thoughts and ideas!

Cheers!