Boxerworks.com

I've had the turkey gobble sound on my '74 R90s for many, many years. The bike has 141,000 original miles with a 1st oversize re-bore at 110,000 miles. At that time I also upgraded the rear main seal with the newer design and it doesn't leak or weep.

The breather valve is the newer reed type and it replaced the original disc type because it was making the same horrible noise. Changing to the reed type did solve the issue until it was re-bored, and obviously the displacement was increased.

The symptoms are that the bike has to be fully warm and it only occurs at idle.

The oil pan is stock and I only keep the specified 2.4 quarts in it.

I know this is common on a lot of bikes but would really like to resolve it if possible.

Different oil pan with increased air capacity?

Less oil in the stock pan?

Go back to the stock breather or change anything with the reed breather?

Thanks for your assistance,
RPG

That sound was very common back in the day (and just as annoying) but I haven't heard many (if any) of the reed types do that.
Sometimes a slightly higher or lower idle speed will fix it.
Does VERY slight pulling of either throttle cable make a difference in the gobbling sound?

Make it a positive like the (terrible) dry clutch noise on a Ducati! it's a unique noise from a classic bike. Embrace it.

More air space should help so I wouldn't run the oil level at the max mark or you could fit a deeper pan. Try it with oil at the minimum mark first to be sure more air space works before undergoing the expense of a deeper pan. I've always been convinced that the turkey gobble noise is made by the rear main seal sucking air in rather the breather expelling air out and that's why more air space helps by limiting the degree of vacuum created. It also explains why another method worked for me. I still have the disk breather and drilling a small hole in the disc pretty much eliminated my turkey gobble noise, presumably making the valve leak a little reduces the vacuum.

Wow! Sounds like a great idea...I've been listening to that sound since '76...never too late for improvements! Thanks for the suggestion Barry

I'm sure RPG will drop back by but on another forum, he posted that he lowered the volume of oil in the sump and the sound went away.

Kurt in S.A.

I apologize by not updating my findings.

I did lower the oil volume by draining the oil and filling with just two quarts. I had always topped it off to the full mark before by filling with 2.4 quarts. With two quarts of oil, the dipstick showed oil at the mark between the two lines. (stock R90s oilpan and dispstick)

Went for a ride and all seemed well. No chirping noise at idle. Then a week later, the noise returned.

So I decided to drain the oil (not including the filter) and measured 1 quart, 20 oz. of oil was drained.

I then re-filled with new oil, pouring in 1 quart, 4 oz, which put the mark on the dipstick at just above the lowest mark.

Then I went for a 20 mile ride, and the chirping noise is still there, just at idle. It goes away at any rpm above idle.

Based on those findings, I don't think it's an over-filling issue.

I realize that a lot of Airhead's do this, but I would like to resolve it, as I did upgrade to the reed style breather AND my rear main seal was updated some years ago.

Thanks,

RPGR90s

Any chance you could use a mechanics stethoscope to try and locate the source of the noise? If it's at the rear of the engine, then it could only be the pushrod tube seals, the breather, or the rear main seal.

Have you done a compression test? Could you are too low which results in blow-by thus filling up the case with air.

Kurt in S.A.

Good morning Kurt,
Actually, using my stethoscope was the next thing on my mind.

I have a nice dual fan setup in my shop for cooling each cylinder, but I only get the turkey gobble after about a five mile ride, instead of just idling in the garage.

I had never considered the pushrod seals as those were replaced about five years ago. Something to check for sure.

I did a compression test earlier this spring and the motor appears very healthy. 150psi for left cylinder, 151psi for the right on a fully warmed motor.