Motorcycle Forum

Motorcycle Forum (http://www.motorcycle.com/forum/)
-   Honda (http://www.motorcycle.com/forum/honda/)
-   -   05 750 Shadow engine knock (http://www.motorcycle.com/forum/honda/15930-05-750-shadow-engine-knock.html)

nahidik 07-26-2010 04:04 PM

05 750 Shadow engine knock
 
My wife's 2005 750 Shadow Aero was running great. Not a problem since day one. I called a mobile bike mechanic to do a yearly service on it. He does a few adjustments, changes the oil, filter and plugs. When it comes time to restart it it is a bear to start. (might have been out of gas in the carb) Finally it runs smooth except there is this rattle, sounds like from the bottom end. It is not constant almost like something bouncing around. When you hold the brake and let the clutch out in gear the rattle is constant almost like a bearing knock. The mechanic says when he pulled the dipstick the bottom portion was missing(chewed off). It was not last time I checked the oil.

So questions are any idea what could have happened to the bottom (1/2") of the dipstick?

Any idea what could have changed with simple oil change and plugs?

other suggestions?

How hard is it to pull the engine down?

I did see the mechanic turn the engine over without the spark plugs in a few times with no oil in it. I don't think you could spin a bearing that quickly.

The_AirHawk 07-26-2010 07:45 PM

Quote:

Originally Posted by nahidik (Post 246641)
I did see the mechanic turn the engine over without the spark plugs in a few times with no oil in it. I don't think you could spin a bearing that quickly.

Yes, you can. The oil-film is the actual "bearing" - the insert and crank pin are supposed to never actually touch - and without pressure to keep the metal parts from touching, it takes only seconds to ruin them - the babbet material is nearly soft as lead, you can scratch it with a fingernail.

I bet he started it without oil in it, when you weren't looking.

Exactly WHY was he cranking the engine over, again? (without oil, that is)

nahidik 07-27-2010 08:25 AM

Turning over engine without oil
 
He had the sparkplugs out and he turned it over probably 6 or 7 cranks while he had the filter off and the oil drained.
I myself am an ex auto mechanic and the average car engine could take this without much problem as there would be residual oil on the bearings and crank journal. However I don't know if the tolerances on a bike engine are much closer. Any idea about the dipstick?

The_AirHawk 07-27-2010 09:03 AM

I wouldn't knowingly turn-over a car engine with no oil in it, either. That residual oil-film will be gone within 2 or 3 revolutions, hence the reason the oil pump is plumbed to feed the main bearings first.

The tolerances are similar to a car's, but on a bit-different scale as to the relation between say bore and stroke, and crankpin-size. A moto doesn't have to move such a large, heavy mass as even the smallest cars, so crankpins and bearings tend to be smaller than they would be for a similar-sized car engine.

IIRC, that 750 Shadow V-twin engine is an iteration of Honda's 52-degree 3-valve water-cooled engine; it has a crank with 3 counterweights with staggered, plain-bearing crankpins between them, and two roller-bearing mains, with the crank driving the wet-type clutch via a gear on the right, and flywheel-stator mounted outboard of the left main, respectively.

The oil dipstick is in the clutch-case (right side of the engine), rearward of the clutch assembly, well out of the way of any moving parts. So, to break-off the end of it, something that moves had to come loose.

Here's a pic from a similar engine, the HawkGT:



Has the bike been dropped on its right side recently? Perhaps a clutch-plate broke, or the basket, or both - and now you've got bits and pieces jangling-about in that section of the engine.

Easiest way to find out, is to pull the clutch case-cover and have a look-see.

nahidik 07-27-2010 09:20 AM

Thanks.

The bike has not been dropped or layed over. If something breaks in the clutch area does it contaminate the whole system? Also when it is not under load the rattling almost sounds like something banging about. Not consistent. However when releasing the clutch with front brake applied it becomes a consistent rattle. Almost sounds like pre-ignition.

The_AirHawk 07-27-2010 09:37 AM

The clutch-case area is part of the engine sump. Anything that's small-enough to become entrained in the oil, will go into the rest of the engine and transmission.

By your description, I'm just about convinced you'll find what's broken when you remove the clutch-cover. It's a "wet" clutch - so you'll have to drain the oil first to keep the mess to a minimum, but that goes without saying.

Hopefully, there's not too much junk being splashed-around. These are hardy, tough and dependable engines that tend not to break unless modified (I know of several examples with over 100k miles). If you find broken clutch bits and a small amount of shavings, clean everything you can and change the oil, and at least clean-out the oil pump (or change it), then several oil-changes at short intervals, and it should be fine.

Probably the life will be shortened of the engine, but by how much, I cannot guess.

The_AirHawk 07-27-2010 09:40 AM

I also should not have to say this, but it's deRigeur for us here at MO - but you should obtain a Service Manual specifically for this bike, ASAP.

Clymer or Honda, both are good.


All times are GMT -7. The time now is 03:55 AM.