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Post by rcq92130 on Nov 1, 2014 18:28:23 GMT -5
VERY INTERESTING!!!!!!!!!!!!!!!!!!
1. So you are also getting vac readings around low teens at idle. Good to now that seems to be "normal" vac for these little mouse fart engines.
2. Can't believe with vac that low the fuel pump even operates! Electric!
3. GREAT to see what normal fuel pressure is. THANKS! The small electric pump I have on now is clearly too much - have not measured, but the spec is 6 to 9 psi. Have been worried it is forcing fuel past the needle valve. The newer pump is rated 2 to 4 psi - PERFECT for this little engine! Think I'll then move the larger (psi-wise) electric pump over to the Goldwing, which has a mechanical pump that sucks and is an Islamic Terrorist. Thanks for the info!
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Post by rcq92130 on Nov 1, 2014 16:49:44 GMT -5
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Post by rcq92130 on Nov 1, 2014 15:47:39 GMT -5
THANKS, Scoot!
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Post by rcq92130 on Nov 1, 2014 13:41:36 GMT -5
ps: probably should ask:
The compression rings were marked "1T" and "2T". I assumed the "2T" was the lower compression ring, marked side up.
Hope that is correct.
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Post by rcq92130 on Nov 1, 2014 13:39:41 GMT -5
Wow! Mine lasted 500 miles or so before biting the dust!
Yeah, in an earlier Thread (2 days ago) I showed photos of the new piston i was about to install - identical to the failed one already in there - and Shannon helped identify I had probably installed the wrong one upside down. Like yours, these 60mm pistons only had an arrow (and on the other side "60"). I didn't interpret the arrow as meaning "Up", but rather pointing to the intake side. Most pistons I've played with are MARKED "in" - so it made sense if they were not THAT explicit they would at least be showing with the arrow which side was 'intake'.
Shannon though the indent on the other side looked slightly larger - thus for the larger intake valve - and sure enough, it's 0.1" larger. Since there was no evidence of contact with the valve, though, I was not comfortable this explained the rapid failure - didn't want to fix this one problem only to find out another thing entirely caused the failure.
Well, anyway, the scooter is back together (this time with the arrow pointing to exhaust) and as soon as the battery is charged will give it a try. Hope the issue is resolved!
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Post by rcq92130 on Nov 1, 2014 12:14:04 GMT -5
Thanks, crr
Yeah - as I said at the top the piston WAS in backwards .... and I was HOPING that was all that caused the problem, though I wasn't very confident of that since the piston looked pretty symmetrical (and thus it wasn't clear why it would wobble). But hopefully that's all the problem is and it's now solved.
Just like Scooter said, I was worried about lack of oil delivery after seeing the gudgeon pin and how it was burned - thought maybe it was freezing up and preventing the piston from rocking correctly (and thus hitting the cylinder wall). It was REALLY a surprise when Alley explained there isn't even an oil delivery path within the rod, and the design depends on 'splashing" to get oil to where it needs to be. I'm kind of amazed this gets a good enough supply to those parts that need a constant 'film of oil' ... but I guess it works OK. Kind of amazing.
But, I guess (hopefully) it's only because of the "backwards" installed piston ....
Thinking of doing a write up for others so they can avoid this. I'm not exactly a novice (compared to most) in tearing down / rebuilding engines ... have done so with a V12, a BMW 6, a Ferrari, a Honda Goldwing, a couple of british sports cars ... And (from the markings on the piston) I STILL made this mistake. A better write-up might help someone avoid things like this (I was using only the Scoot Dogs video, which glosses over a lot).
Anyway, thanks much for the info!
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Post by rcq92130 on Oct 31, 2014 19:54:39 GMT -5
Hot as in "lean mixture", or hot as in "needs an oil cooler"?
Or just "hot' as in the rings were not conducting heat away from the piston becasue of the damage?
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Post by rcq92130 on Oct 31, 2014 19:53:45 GMT -5
Oh. Thanks! I was hoping that might be the whole problem, but didn't understand why it WOULD be (and the burning on the gudgeon pin made me think of "oil shortage' of some kind.
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Post by rcq92130 on Oct 31, 2014 19:36:42 GMT -5
Yes, I said this at the very top of the post.
My question was - and is - if this would cause this kind of damage. The piston appears symmetrical (other than the indents, which are 1/10th of an inch different), so it's not clear why the piston would wobble (unless a valve struck it, which does not look like happened).
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Post by rcq92130 on Oct 31, 2014 18:56:21 GMT -5
The mystery of why the BBK had gone bad (low compression, blowby) are becoming more clear as the pix of the piston and cylinder liner make clear. But I'd very much like to hear from anyone as to WHY this likely happened so the new BBK (just installed) does not suffer the same fate. The piston WAS installed "backwards" (indent for intake valve down & that for exhaust up) - but there does not seem to have been any valve-to piston contact ... and the piston seems to be symmetrical other than the indents, so i doubt being backwards caused any 'wobble'. Pix of piston from 180 degrees apart:  and from the other side  Notice the lower compression ring - pushed and stuck all the way into the grove (and, seemingly, ground down). With great effort i was able to remove this ring - which looked not bad (and the right inner & outer diameter) once removed. But it was indeed jambed in tight into the groove! Here are 2 pix of the cylinder liner--- scored, of course, but only a few that could be felt to the touch:   And here is a pic of the gudgeon pin --- discolored from heat on both ends.  AGAIN -- ALL THIS HAPPENED IN ONLY 600 OR SO MILES. Did NOT run low on oil; did NOT have the incorrect oil in the crankcase. I'd dearly like to not have this happen again, but am not sure WHY this took place. Any experts able to shed light on this? |
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Post by rcq92130 on Oct 30, 2014 20:10:36 GMT -5
I wonder if that is the cause of the early failure. This is a crappy photo (of the initial BBK install), but you can see the "60" at the BOTTOM (exhaust side), which i guess is WRONG:  There isn't any obvious evidence of valve-to-piston contact, but maybe at high RPM (for me only 7,000) the two WERE contacting, and maybe the valve bent just enough to mess up compression (and performance). No EVIDENCE of that, but if soot then covered over any shiny marks ... Or maybe I'm just grasping at straws. Anyway, it DOES seem i installed the piston upside down. |
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Post by rcq92130 on Oct 30, 2014 19:41:33 GMT -5
BTW, someone asked that I measure the actual size of the piston to see if "60mm" is true or a lie.
At the top (above the #1 ring) the diameter is 2.342in (that's 59 1/2 mm)
At the skirt the diameter is 2.365 in. (that's 60mm)
I don't have a proper micrometer to measure the inside bors of the cylinder liner, and with the mic. I have am getting measurements SMALLER than the piston skirt (2.362 at the top, 2.360 at the bottom), which is obviously wrong since the piston slides easily inside the liner (brfore the rings were installed, of course).
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Post by rcq92130 on Oct 30, 2014 19:32:31 GMT -5
Thinking the reason the last BBK install failed (after only 5 or 6 hundred mi!) is the piston was in upside down. Here is a photo of the piston, with the sizes of the indents:  During the first install - no directions included in kit - I thought ("ASSumed") the arrow etched onto the face of the piston pointed toward the intake side, and installed it with the arrow pointing "up" when installed. But measuring the valve indents, the one next to the etched "60" is larger --- so, probable for the intake valve ... right? Or is that wrong .........  ? |
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Post by rcq92130 on Oct 30, 2014 17:02:01 GMT -5
are you sure i will need to have an oil cooler with my little 60mm bbk?
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Post by rcq92130 on Oct 29, 2014 15:36:57 GMT -5
They DO make a great, comfortable seat. It's called a Honda Goldwing.
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