One for the 250cc folk

[generatorshovel]

How far up are the plug threads showing color?  Just curious.

When testing #4 burnt 1/2 the earth strap from the plug (#500 main) , I had a "safe" #640 in it when the piston melted, I will never know if I began to melt the piston then, or not, if so, the piston would have been very weak on the crown
While pulling the piston off the rod, the pin was tight,,and the top ring was also tight, poor little piston had a hard life

All the plugs show only up to one thread discolored,

[DND]

Hi Tiny

Maybe a new manifiold is in order, a log or plenum style with the same length runners.

The one you have now just might be giving the different holes different mixtures, worth a little fab time to make a more efficent system so each of the 4 guys are getting the same load.

Don

[maj]

I think the same as Dave and Don
looks like your getting less fuel on the hurt cylinder
my best guess ,  supercharger is probably directing the methanol as a liquid more than vapor and flinging it towards the upper tubes from the lower half of the supercharger
only 10% less flow to the cyl could be enough to cause problems

[generatorshovel]

Thanks for your input guys, there's nothing like a think tank
The plenum change makes sense , it might even end up being easier to fit,,surely it won't be harder,,,,,
Funnily enough, the original plan was for a "normal" type plenum, but was dropped after trying to think like a pocket of fuel / air mixture, and how it would behave,,best I revert to not overtaxing my last 3 remaining brain cells, and do more research,
EDIT,,,
Space is always a problem, the frame rails do not allow any other intake at the moment, so it's time to reinvent the wheel,,,,,
My co-builder always wanted to build a sidecar,,this engine is a test bed for it,,,I think , with all the input received from you guys , and the gut feeling I've had regarding the plenum appears to be true,
I absolutely HATE working on fiddly things, so the new frame design needs to allow the engine, or parts attached to it to be easily removed when needed . I'm thinking no backbone, maybe a removable one, , structural strength can be designed without the need for a backbone, and the different layout of a sidecar frame will allow for thinking outside the square ?
Although designing a better plenum will be a challenge (I still worry about cylinders #1 + #4 not receiving as much mix as #2 + #3). but if I build a blower / plenum test bench and measure each cylinders flow rates while spinning the blower with a drill or simillar, changes can be made inside the plenum untill I'm happy with the result ?
Long & low is the plan, detachable 3rd wheel on a stick  maybe ?
Tiny

[Peter Jack]

While you're at it I'd be tempted to make the flanges out of somewhat heavier material. A leak in one location could definitely affect the mixture in the area of the leak.

Pete

[JimL]

 I see heat line almost to the top of the threads.  Thats a little spooky.  Not the carbon line, but the metal discolor.

Thats too far for extended run.  Once you get that kind of heat flowing through the shell, youve leaned out and the pistons are toast.  It takes time and distance to heat soak an aluminum head to the point that it stops accepting more because the only path left for the calories is into the coolant.

Many of us with marginal cooling capacity, for our power output, try not to sink too much heat into the head before we start our run.  When we get it right, the engine gets about good in the mile that matters, though it is feeling a little raggedy in the first mile or so.

I havent blown an engine up since I was taught to do it that way.  My plugs come out without a color line, so I could be a little more brave but I have that Italian disease...."mufunzalo".

Anybody else here seeing that hot steel color way up the threads?  I aint that sharp on this stuff, so steer him right if I'm off base!

Thanks

[wobblywalrus]

The bottoms of the pistons show that things were getting pretty hot in all four combustion chambers.

[DND]

I was looking at your blower pic and it looks like you can see the bolt shank between the two center flanges, oops not too good as this would leak out your boost.

Like Peter Jack says you need thicker flanges and make sure they are flat after your welding too.

That sure is a neat little blower, what was its main use?

Don

[Grandpa Jones]

Hi Tiny,

Found some intake manifold pictures on the SOHC Honda forum. Didn't want to post the pix
without permission, so here is a link.

http://forums.sohc4.net/index.php?topic=101267.100

I guess with the inlet being offset from the runners, the flow from the turbo/blower can't
favor one runner over another. Boost/mixture hits the "wall", and is diffused into the plenum.

Charlie Toy went fast with a draw-thru turbo, scroll down the page and you can see this
type of manifold on one of his bikes.

http://www.landracing.com/forum/index.php?topic=3972.0

Cheers,

Dave

[wobblywalrus]

Type "48.5mm pistons" into your search engine.  Aliexpress.com pops up.  They have your pistons.  They are made by lpmotoparts.

Send me a pm if you can't find them.

[generatorshovel]

JimmyL, the plugs have oxidised quite a lot sinse they were pulled, I pulled # & #4 on the salt (the others take 1 hr) #1 had thread heat discolourisation on 1 side of the 1st thread only, and 4 was contaminated when the hole appeared
#2 & #3 had one complete thread discoloured when they were eventually pulled

Wobbly, the engine has done 24,000 liles before I bought it, I suspect the gold under the piston crowns was a result of the test ride when I melted the plug from #4
I don't trust the Chinese, they have already planted a virus enabling them to change a cut & pasted email address so they got $200 of my hard earned,,PayPal told me to go plait my sh*t
Honda make good pistons, but not good enough,,custom flat top forged with ceramic tops should be up to the task, an egt gauge is a must
I wont buy chinese,,EVER, if I know who made it first

DND,,the blowers were used on Subaru Vivito 660cc delivery vans in Japan only-- point taken on the flanges (they were 8mm plate before being milled flat---

Dave,,anything I've posted is considered public , anyone can re-post, but thanks for the consideration you showed
Tiny

[DND]

Tiny you were saying that the coated pistons would be a good deal, maybe not if the heat kills your 4 valve head.

Might be better to hole a piston than kill that neat little 4 valve head !!

Don

[Dr Goggles]

I absolutely HATE working on fiddly things, so the new frame design needs to allow the engine, or parts attached to it to be easily removed when needed . I'm thinking no backbone, maybe a removable one, ,

just make up some mini exhaust type flanges, or a pipe sleeve for the top tube , or tell me to GFM, no, not "go find mum"

Spoke to Frase on Sun night, thanked him for feeding us orphans , he told me the high point of the week was the old fellas whinging about the chili c.c, I brought up the big-block, he changed the subject.

[generatorshovel]

Tiny you were saying that the coated pistons would be a good deal, maybe not if the heat kills your 4 valve head.

Might be better to hole a piston than kill that neat little 4 valve head !!

Don

Don, A ceramic coating may give me some time while I sort the mixture, heads are a dime a dozen if you are patient, valves, they are another story,,,,

Goggz,,GFY  :lol:
Wilso boned up when I told him the plan, and started muttering things like,,110" wheelbase,,rear engine, inverted wing chair structure, doubling as fuel tank nsr single sided swing arm,,mutter mutter,,
Still trying to get to Sunshine to see a man about a dog,,,
T'fer

[wobblywalrus]

Tiny, that idea of a log type plenum with equal length intake stacks is a good one.

The Triumph runs on pump gas on the street.  It is near sea level here and it is jetted for unleaded non ethanol pump gas on the dyno.  ERC MULB, an unleaded racing gas, or ERC 110K, a leaded racing gas are used at B'ville which is at just over 4,000 feet elevation.  The bike runs OK on those race gasolines with no jetting changes on the salt.  This tells me those race gasolines may be oxygenated and I could burn up the engine if I used them at lower elevations - unless I jetted the carbs richer.

I am not familiar with how you did the jetting or the equivalence of Australian race and pump gas.  It is something to consider if the bike was jetted for pump gas and raced with an oxygenated one.