Author Topic: One for the 250cc folk  (Read 101348 times)

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Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #30 on: February 23, 2013, 10:33:11 PM »
Tiny, on no!  At least it was a non-violent engine failure.  Try to post some close up views of your spark plugs and the undersides of your pistons when you get it apart.  It sure sounded good when it was running on all four.

Offline Old Scrambler

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Re: One for the 250cc folk
« Reply #31 on: February 23, 2013, 10:39:39 PM »
You were very cool and under control when the bad sounds appeared :cheers:  I think we all feel for your carnage but we still want to see pics of the real thing...........maybe we can learn a lesson to three :lol:
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

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Offline generatorshovel

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Re: One for the 250cc folk
« Reply #32 on: February 23, 2013, 11:37:24 PM »
I'll post the autopsy pics when it happens, NP
I had a bloke wanting to buy it early in the week, I didn't say no, just see me later in the week, adding it may have a ventilated crankcase by then, so I was expecting trouble so a mere holed piston was a relief.
1st job is to fit the EGT, 2nd is to drown every bolt in WD40, as this will be the 1st time it's been opened  :oops: and they have a habit of snapping cam bolts.
It may have sounded sweet, but it wasn't, my last test run was sweeter than illegal thought, with a 580 main, I fattened to 600, then the more I thought of its future,,went up to a 640 main, it didn't like it much, but cleared in 4th, up until that, my right wrist looked like it was opening screwtop beers, feeling for the sweet spot, on the previously mentioned test, I hardly had time to select the next gear before hitting 1700 (which is 16200 btw) @ WOT
My cool had vanished after pushing it for 1/2 mile I can assure you  :evil:
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline gearheadeh

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Re: One for the 250cc folk
« Reply #33 on: February 24, 2013, 03:56:21 AM »
Feel for you, Iam a fan of your efforts and look forward to more info.
40 is the old age of Youth, 50 is the young age of the Senior years.

Offline Stan Back

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Re: One for the 250cc folk
« Reply #34 on: February 26, 2013, 10:30:00 PM »
250!!!  How fast did it get to?  Overshot the return road -- none of us has ever done that.
Past (Only) Member of the San Berdoo Roadsters -- "California's Most-Exclusive Roadster Club" -- 19 Years of Bonneville and/or El Mirage Street Roadster Records

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #35 on: February 26, 2013, 11:58:17 PM »
Autopsy pics


#4 cylinder arrowed (the holed piston was #4)



Water got into #1 as I hosed the salt off , numnuts me didn't re-tighten the plug after removal for inspection saltside.
Tiny

PS, Stan, who overshot what ???? where ?  :? :? :?
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #36 on: February 27, 2013, 12:37:14 AM »
It looks like there were similar piston crown erosion problems on all cylinders and only one had enough of a problem to burn through.  From what I see, this was not the case.  It seems that the problem was on the one cyl only.  A problem with an advanced spark would show up on the cyl on the other end, too.  It looks like it did not, so the timing was OK.  It seems a lean mixture might be the problem.

Offline Stan Back

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Re: One for the 250cc folk
« Reply #37 on: February 27, 2013, 12:42:53 PM »
I thought at the end of the video that the rider crossed over what I took to be the return road.
Past (Only) Member of the San Berdoo Roadsters -- "California's Most-Exclusive Roadster Club" -- 19 Years of Bonneville and/or El Mirage Street Roadster Records

Offline DND

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Re: One for the 250cc folk
« Reply #38 on: February 27, 2013, 03:31:23 PM »
Hi Shovel

The crank must look a bit odd with the end throu hanging out a bit to make room for the cam drive stuff.

Its a shame you holed a piston but at least you don;'t have a rod throu the case.

Need more fuel !!!

Sure liked your video and neat sounds too.

Don

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #39 on: February 27, 2013, 04:20:38 PM »
I thought at the end of the video that the rider crossed over what I took to be the return road.

Ah HA,,now I understand , that was the Fire & rescue road, once I'd crossed that, the track was clear.
Tiny
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #40 on: February 27, 2013, 04:31:43 PM »


The crank must look a bit odd with the end throu hanging out a bit to make room for the cam drive stuff.

Its a shame you holed a piston but at least you don;'t have a rod throu the case.

Need more fuel !!!

Sure liked your video and neat sounds too.

Don

The crank extension is supported by a hybrid ceramic bearing, there was 3 poofteenths room for the shaft to pass the hall effect sensor wire.
Throwing a leg outa bed was expected.
I think I'd started a piston crater during testing, when I burned a plug earth strap #4 plug with #500 main jet, subsequent tests were done with #580, then #600 main, the #580 was not leaning out, the #600 was "safe"
I burnt the piston using a #640 main, the engine didn't clear until hitting 4th gear (the 2 mile ride to the line wasn't such a good idea), and power was down .
The ironic part of the story is that I have an EGT gauge in the filing cabinet, but chose not to use it, as they make you worry too much  :oops:
It will be fitted now, after the horse has bolted
Tiny
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline DND

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Re: One for the 250cc folk
« Reply #41 on: February 27, 2013, 07:53:46 PM »
Hi Tiny

That egt sounds like the way to go , as you sure don't wan't to hurt that neat little engine anymore than you did.

Don

Offline wobblywalrus

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Re: One for the 250cc folk
« Reply #42 on: February 27, 2013, 09:13:36 PM »
Did the other three cyls have the same size jets and no problems?  If so, the main jets can be big enough and there is another restriction somewhere in that carb or the float level is off.  Or maybe there is an air leak on that bad cyl.

 

Offline generatorshovel

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Re: One for the 250cc folk
« Reply #43 on: February 27, 2013, 09:50:07 PM »
Did the other three cyls have the same size jets and no problems?  If so, the main jets can be big enough and there is another restriction somewhere in that carb or the float level is off.  Or maybe there is an air leak on that bad cyl.

 

One carb, 8 lb boost, leaks would be to atmosphere, not drawn in.
Tiny
Tiny (in OZ)
I would prefer to make horsepower, rather than buy, or hya it, regardless of the difficulties involved , as it would then be MINE

Offline gearheadeh

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Re: One for the 250cc folk
« Reply #44 on: February 28, 2013, 01:44:20 AM »
Instead of looking at the fuel is it prudent to wonder if that 1 cylinder sitting off by itself will run a little hotter than the others, just enough that it goes over the edge first!
40 is the old age of Youth, 50 is the young age of the Senior years.