Octane rating?

[keelerb]

I have an 84 R100RT. Have always used 87 (R+M) octane "regular" without any apparent ill effects, but last weekend doing 80s or so on the highway for a couple hours, I thought I detected occasional pinging under load (passing, etc.).

Does this sound right? From memory, this thing runs about 8.2:1 compression ratio. Pretty low. I've never understood it to need higher octane.

Having said which, when the tank was half full I pumped in a few gallons of premium and didn't experience the "pinging," if that's what it was, again. Placebo effect, possibly.

Welcome your views. Thanks - BrianK

[Manfred]

At what RPM did you hear the ping?

(My inner "Sean Connery" wants to know - was it one ping or two?)

[keelerb]

Gosh, would have to be somewhere between 4K and 5K-ish I think. Wasn't lugging it, I assure you. But it was probably at 7/8 throttle and going WOT would cause the - alleged - pinging. Any thoughts?

[Manfred]

If your RPMs in that range and the bike was not laboring (as in uphill), low octane detonation doesn't make sense.

When's the last time you checked your valve clearance?

[keelerb]

Valves checked and left at .006" intake and .008" exhaust not more than a month and very few miles ago.

Agree, hence my confusion!

Didn't really sound like the pinging I've heard before (like riding a rented HD in Arizona desert in the summer using the crap gas they sell there, or using my until-then-satisfactory low test in my Ducati 900 SS after installing high-comp pistons and before retarding ignition).

But it sounded more like pinging than anything else I could come up with by way of explanation.

[Manfred]

I imagine it's kind of difficult to assess where the noise is coming from, considering the RPMs you're turning. Could it be the noise ain't coming from the top end?

[keelerb]

Certainly could. I just couldn't figure out WHERE. That big noise-reflecting/refracting fairing is not helpful in this regard.

[Manfred]

A suggestion: When I'm trying to hear my engine, I duck my head down below the windscreen and I hear a whole lot dorect engine noise than when I'm sitting up and the fairing and windscreen are masking it.

[keelerb]

Yeah, I know; this was more "transitory," if you will - when it happened, I was surprised and by the time I could pay attention, it had stopped.

The more I think about it, the less it seems to me it could be pinging. But I can't figure out what else it could be.

Thought: Do these bikes have universal joints (they must?!) - I remember from my youth the sounds bad (?) universal joints would make when they were stressed in usage - a sort of "diesel rattle." I wonder if it could be something like that?

[Manfred]

They have a U-joint at the drive hub - see this picture (http://www.realoem.com/bmw/showparts.do?model=0464&mospid=47899&btnr=26_0111&hg=26&fg=05).

If you can detect that the noise is coming from "under the seat", as opposed to behind you, it ain't the U-joint.

Since it's intermittent, could it be any other simple thing? For example, I mounted a compass on my dash and at idle, it rattles sometimes. Took me a while to figure out what that noise was.

[keelerb]

Dunno, have to figure it out next time it happens! This is my winter/highway bike, so could be a while. I think we've convinced me it's not pinging. On to the next theory. Thanks for your help!

[Manfred]

I re-read your initial post. Play with the fuel some more and see if that makes a difference. It's the simplest diagnostic I can think of.

It takes a village to keep an old bike runnin' :-)

[osbornk]

You may have just gotten some lousy gas.

[PMonk]

During hot weather you are more liable to have pinging because motor is hotter. Try 89 octane. How much carbon do you have on your pistons and heads? That increases your compression ratio causing pinging.

I am dealing with that now. I have tried larger main jets, Have Omega ignition set slightly retarded to reduce pinging (usually hot weather on uphill). After the Honor Run ride saturday I am replacing the original crankcase breather with reed valve type. I know the old one isn't working as I have found oil on the garage floor under my right carbeurator and a heavy coat inside air tubes. I figure all the oil that I have been burning has to have left a lot of carbon in the comb. chamber so probably am going to pull the heads for cleaning also.

[keelerb]

Fuel comments may have merit. First, as I said this is primarily my winter bike. So it's been sitting a bit. Fuel may be old

Second, plugs look a little whitish (although it's difficult, at least for me, to read plugs in these days of unleaded gas and ethanol, and I didn't do actual plug chops, just pulled them after I got home), and I got 45 MPG doing 80+ MPH this trip, so it may be a tad lean. I'll look into that.

Thanks folks.

[jforgo]

I have noticed issues with the crap ethanol gas around here when the temp gets around 100. Parking in the sun doesn't help on those days either. As air cools off, sun goes down, no problem.

The corn agrimegabiz is pushing for approval of 15% stuff, BTW.

[PMonk]

They understand well that we have the best politicians money can buy!

alcohol as fuel:
less mileage, less power, higher food prices, killing the fish in the Gulf of Mexico (due to fertilizer washing down the Mississippi), increased water demand to process corn into something you can burn, big bucks in politicians pockets,
What's not to like?

[jforgo]

They understand well that we have the best politicians money can buy!

alcohol as fuel:
less mileage, less power, higher food prices, killing the fish in the Gulf of Mexico (due to fertilizer washing down the Mississippi), increased water demand to process corn into something you can burn, big bucks in politicians pockets,
What's not to like?

hey now! We're "goin green" hyuk hyuk