Engine rebuild...

[Houtman_imp]

Deutz made great air cooled tractor engines , little noisy but lasted forever on the farms.

[pekingduck]

Here's my thoughts on what happened. I assume the onset of the vibration was fairly sudden, and it wasn't ridden much after it started. The visible scuffing on the pistons and cylinders is not abnormal. Four cylinder engines running on 3 cylinders don't really vibrate more, so I don't think the bent valve is the cause - maybe just a red herring here.

The carbon buildup may be caused by a poorly re-mapped ECM that causes it to run rich - or something like leaking injector(s) or a fuel pump with a regulator that is out of spec. That can be tested easily by the dealer with a fuel pressure gauge, turning the key on momentarily to energize the pump, and see if pressure bleeds off. Its should be 50psi, not higher, and should hold for 10 min.

The likely cause of the vibration is a bent rod(s) from hydrolocking, from fuel or water filling a cylinder before it is cranked. It happened several times on 1979 CBXs that developed sudden vibrations. They were left on the sidestand with the fuel valve left on, one of the float needles might stick open, and fuel would fill the primary airbox and fill the far left cylinder (vacuum petcock added in 1980).

I have also seen plenty of bent rods on ATVs are submerged, but also that are pressure-washed and water is shot into the exhaust or intake and into the cylinder.

When they pull the head off again, they could put each piston at TDC and see if one or more does not come up as high. It would be pretty noticeable, maybe 5-8mm difference.

[peterbaron]

The above explanation is logic...
WHAT I cannot understand is, WHY dealer released the bike...correct me if I am wrong (bike in your possession..or at the dealer premisses??) [/i]

[pekingduck]

There are two other causes of carbon buildup that can be owner induced.
First, higher octane fuels do not burn as quickly and will lead to more carbon buildup over time. They don't produce more power, and you're not doing the engine any favors to "treat it to" higher octane.
Second, when the bike is just started up cold, the ECM is on a richer cold-start mixture, which is fine. Blipping the throttle gives an extra-rich mixture that doesn't burn completely, and the cylinder walls get washed with unburnt fuel that can wash oil film off the cylinder walls and cause some of the scuffing on the pistons and bores.

[peterbaron]

There are two other causes of carbon buildup that can be owner induced.
First, higher octane fuels do not burn as quickly and will lead to more carbon buildup over time. They don't produce more power, and you're not doing the engine any favors to "treat it to" higher octane.
Second, when the bike is just started up cold, the ECM is on a richer cold-start mixture, which is fine. Blipping the throttle gives an extra-rich mixture that doesn't burn completely, and the cylinder walls get washed with unburnt fuel that can wash oil film off the cylinder walls and cause some of the scuffing on the pistons and bores.

..and this is correct again, +1

[DBM_imp]

I always allow my engine to warm up at idle for at least a minute before l touch the throttle. This tip was given to me many years ago by a pro level engine builder. I have been using only top tier 93 octane in my new scoot since new. Are you saying l should use 89 or 87 octane insread?

[the Ferret]

There are lots of wives tales that will probably never die. Using an octane too high for the compression is good for the engine, is one of them. If the manufacturer calls for 87 (which the CB does) then using 89 or 93 is a waste of money as it wont properly burn, it won't burn cleaner, and it won't produce more power ... but a zillion " old timers and promoters of the wives tales" will tell you differently.

What MAY make a difference is either burning an 87 non ethanol gas or burning a tier one 87 octane gas which has additives to actually clean up your valve seats, stems and piston tops.

Honda says their engines are designed to run on up to 10% ethanol but no higher. I have never read a study saying ethanol was bad for engines, however I have read where it is bad for rubber and plastic parts. I have also read that it takes more ethanol to produce the same amount of energy than straight gas

If you hang around enough forums you will find many who believe they know more than the engineers that designed the product, and who truly believe the stuff they hear from relatives, friends, neigbors and the local grease monkey with the high school education that has worked on engines "all his life" and will then continue to spread that (mis)information, whether it is based on fact or not.

Try googling some things like " is burning higher octane better for your motor" or "is ethanol bad for your motor", read some findings and make up your own decision, then make your purchases based on that.

Beware of anecdotal evidence, that is not really evidence, but hearsay and happenstance.

[SportsterDoc]

1. 87 octane, as Honda recommends. Higher octane burns slower, to avoid detonation.

2. Top Tier fuel, for minimum deposit accumulation and possibly remove some already accumulated.

3. Minimize idling. Cold idle is rich. Start it and ride easy for a couple miles.

4. If your riding requires a lot of short trips, get out on the higher speed roads regularly. Get the engine heat saturated.

Just my 4 cents

[Cormanus]

Well said, Ferret.

[SportsterDoc]

Well said, Ferret.

Ditto and ditto to pekingduck