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Author Topic: One for the 250cc folk  (Read 40696 times)
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tauruck
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« Reply #195 on: January 14, 2016, 11:40:03 AM »

At least it's not a d$%K in a shirtsleeve?. grin
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generatorshovel
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« Reply #196 on: April 07, 2016, 08:59:01 PM »

The horse is not yet completely dead,,but needs resuscitation, again,,,
The engine didn't enjoy a feed of Teflon, but most if it parked itself against #4 cyl intake valves, which seems to have contributed to the heat build up in that cylinder, it didn't help that, in my rush to leave for the salt trip , forgot the correct carby slide, the one that was in it had been trimmed to lean off the gas (post methanol use) mixture.

Maximum blower rpm is 11,250 (15,000 engine rpm)


My extremely meager race budget does not allow for coughing up over $3,000 to get custom forged pistons, and I know I'm really wasting my time using cast krap, but they have "sorta" worked in the past,,,with 10 lb boost, so I'll go back to 5 to 8 lb, reuse the stock cams (lots of overlap) , and rev the Krap out of it again next (my last attempt with this one) year
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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
wobblywalrus
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« Reply #197 on: April 07, 2016, 11:23:26 PM »

Is there a black or dark brown stain from oxidized oil at the centers of those pistons on the undersides of the crowns?  Can you show close up pictures of any problem areas on the pistons?
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generatorshovel
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« Reply #198 on: April 16, 2016, 06:46:46 PM »

I haven't looked yet Bo, I'll leave the pistons on their individual rods 'till the new pistons return from the ceramic crown treatment, less chance of mixing 'em up that way  rolleyes
The failure had many  contributing factors, hotter plugs, wrong carb slide,power jet isolated etc. , I thought it strange the egt's didn't get over the high 800's (f) huh , although I wasn't riding it & can only rely on the video and feedback from a rider who has very little seat time on the bike.
 I'll go back to the "safe" tune I used last year, back the boost off a tad, cooler plugs, slightly richer (than last year) mixture using the power valve in an attempt to do the timer trip trick, in top gear, and with water wetta in the system, not just air,,,, shocked
Boost can always be increased when needed, on the salt.
Tiny
« Last Edit: April 16, 2016, 06:49:10 PM by generatorshovel » Logged

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
wobblywalrus
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« Reply #199 on: April 16, 2016, 11:55:56 PM »

The ceramic treatment was what I was going to suggest if the oxidation on the underside indicates the center of the crowns are getting hot.  It seems that you are doing this.
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generatorshovel
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« Reply #200 on: April 27, 2016, 02:31:33 AM »

Here you go Bo,,,



* Bo pic.jpg (218.05 KB, 822x567 - viewed 211 times.)

* New'n'old.jpg (204.35 KB, 822x567 - viewed 200 times.)
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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
wobblywalrus
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« Reply #201 on: April 28, 2016, 12:18:23 AM »

There are shiny areas on the upper skirts on the outer pistons just below the rings.  Does careful examination indicate those two got hotter and expanded more than the two inner ones?
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generatorshovel
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« Reply #202 on: April 28, 2016, 04:33:49 AM »

The black areas is  a Molybdenum Disulfide DF1 coating Bo, it wears off real quick,,,,
#2 piston has only done 6 miles work, mostly at full noise, the others have had 2 years worth of abuse( 10 miles?) grin
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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
wobblywalrus
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« Reply #203 on: April 28, 2016, 07:57:21 PM »

Sometimes the ignition trigger coils or the ignition triggers on the flywheel are out of alignment.  This affects the timing curve of either the two inner or the two outer cylinders.  It looks like only one is having problems is that outer one so that cannot be an issue.

Many times I used cast pistons in applications where forged would be proper.  One problem with the cast ones was the lack of thermal conductivity on the crown and this resulted in hot spots.  The ceramic coatings will help with this, I am told.

Sometimes that problem is seen on the cylinder whose carb is furthest from the fuel supply.  It starves for gas first 'cause it sucks hind tit, as folks say.  It goes lean and the piston crown melts.  As I recall, there is a single Weber or Holley for all four cylinders.  This probably is not the problem.

The only thing I can think of is fuel condensation.  The fuel is condensing on something and it flows along the walls of the inlet tract to some cylinders but not all.  Or, it condenses and revaporizes in a way that gives that end cylinder a lean mix.   
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generatorshovel
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« Reply #204 on: October 02, 2016, 07:10:40 PM »

I'm slack with updates, sorry,,,,
Most of my problems this year were a result of a very poor valve seat job, plus some impregnated alloy in the valve faces, the problem was cured by doing the job properly, myself,,A job not made any easier by the valve seat dia being smaller than the smallest Neway cutters, but , as usual, they were modified to do the job.
Another problem reared it's ugly head when putting the "stock" cams in, in an attempt to detune the setup a tad, these cams have 1mm more intake lift, the problem I now have, is .001" less piston/ valve clearance than I have lift, this took some research & careful measuring, and I discovered the pistons I am using have .96 mm higher domes,,,,,than stock
Measure twice eh !  rolleyes
Tiny
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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
wobblywalrus
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« Reply #205 on: October 02, 2016, 07:35:10 PM »

The same thing happened to me when preparing the Triumph for Pendine.  Some late night work with an angle grinder on the piston crowns did the trick.  The valve pockets were deepened in the pistons.  It takes a pint or three to calm the mind and steady the hand before that sort of precision work.
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generatorshovel
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« Reply #206 on: November 03, 2016, 06:25:40 PM »

It seems I'm the only person to ever try to repair these bike(ette) engines , EVERYTHING needs to be special order, even to machine the minuscule 16.5mm exh valve seats (3.5mm valve stems)
 Dead Horse
Tiny
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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
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« Reply #207 on: November 03, 2016, 11:39:23 PM »

On the Triumph, these are modified stock:  cylinder head and crank.  These are special order:  rods, crank and rod bearings, pistons, rings, and pins, cylinders, head and base gaskets, valve seats, valves, springs, guides, keepers, tappet buckets, valves, cams, cam gears, clutch plates, clutch springs, ignition module, coils, spark plugs, exhaust system, intake manifolds, carbs, and air filters.  Sometimes I wonder why it is called a Triumph on the entry sheet.  "Mongrel" would be a better description.  Do not feel like you are alone on this matter.   
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generatorshovel
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« Reply #208 on: November 04, 2016, 01:24:09 AM »

I don't mind the challenge of finding the "right" parts Bo. but the waiting for them to be made & delivered sure frustrates the hell outa me,  my hates also include deadlines, and being forced to try to "compromise", as it usually leads to failure.
 Why is a good,cheap build idea always transformed into a 5 year expensive addiction ? has stubbornness got anything to do with it ?
Tiny
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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
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