Looper exhaust porting

[powerabout]

A lean sneeze that stalled engine so had time to burn yet the Captain says it never missed a beat?

[FMP]

What's the blowdown interval, the high boost ports? Double, cross firing ign?

[Captain75]

A lean sneeze that stalled engine so had time to burn yet the Captain says it never missed a beat?

Only backfireing in the exhaust, never carb side...
Just realized that the sudden idle problems I got during and after a long trip this summer probably appeared when the idle relief stuffers was burnt away (post #567)

No thoughts on exhaust liner?

[Captain75]

The more I look at things the more certain I become that the cylinder scuffing was caused by a too generous amount of clearance(piston tilting from lack of support from opposite Wall) However I need to wait and confirm with a bore gauge.
If this seems to be the case I will order some WSM .010” pistons and start to enlarge the bores with the 80grit Stones...
Whats the better choice: Pistons with f/p holes already in place or the early big bore Pistons with ringstops in f/p area (I drill f/p holes myself)??

[FORBESAUTO]

The best option would be get your bore gauge, go at least 0.010 inch larger and get it bored. If you open it up much with a hone, almost always gonna end up with taper in cylinder with the bottom being smaller than the top. The bottom will not not get near the amount of strokes the top will get due to trying to stay off the floor.

[FMP]

As already suggested fit your used rings at various depths and check fit and gap, compare to your records before running. Measure ring widths difference from ex to transfer side and compare ring wear to bore shape.

[powerabout]

Drill your own finger ports, you can put them higher and on a better angle than stock

[Captain75]

No water in the fueltank!
Concerning the idle reliefs: Straight, non tapered Allen screws could probabably do the trick, question is weather std Locktite thread lock could cope with the heat?? Still can´t understand why the JB Extreme didn´t work when people on this board are using Marine Tex??
I posed another question earlier (lot of q`s...)Do I have anything to gain by cutting the exh liner just below the flange? More space for the gasses to expand at take off!?

Look forward to your thoughts and insights!

Standard M5 thread fit perfectly!





Perhaps som JB Weld as thread lock?

About cylinder wear and Bore size:

I have avsked some questions in another thread concerning piston to wall clearance:
Due to the cylinder wear I have suspected a too big clearance that perhaps allows the piston to rock a bit in the bore, at least when cold.
I don´t own a caliper with long enough jaws, but with an alternative method I got some preliminar results:
Piston size: 93,30mm (3.673”) 90 deg from wristpin, at the height of wristpin.
Bore sizes: + 0.0086”- 0.0098”, all bores are straight, measurement at serveral spots at various locations and heights.
Even though I don´t have the proper caliper, it feels like the Pistons are too loose in the bore!
I am considering to buy six .010” WSM Pistons, these should almost slide in there right now. Just carefully hone the bores to spec (my wisecos says +0.003 on the box)

Any ideas?

[mholm]

Doesn’t it say on your wiseco box what bore size should be?

I have bored my 90hp yamaha and waiting for Wiseco pistons. On their website is the bore size for each piston size.

Have you chamfered the cylinder ports? I read back and looked at your pictures and couldn’t see any chamfered ports. Wiseco says ports should always be chamfered. I did mine after Jennings Two Stroke Tuning Handbook with a dremel . See pic.


Do you think that the rings could had snug in the ports and caused wear in the cylinder? Just throwing out some ideas.

[NosBoss]

Pistons are to be measured at the bottom and 90 degrees to the wrist pin. You really need to get the proper measuring tools for the job. Otherwise the results may not be correct.

[Captain75]

Pistons are to be measured at the bottom and 90 degrees to the wrist pin. You really need to get the proper measuring tools for the job. Otherwise the results may not be correct.

Ok, apparently different methods out on the board. Look at post #26 in the thread wiseco clearance.

[powerabout]

IMHO, I would start with the bore measurement and how much it is over stock is your added clearance for a forging before you need to worry about 50 ways to measure a piston

[NosBoss]

Ok, apparently different methods out on the board. Look at post #26 in the thread wiseco clearance.

Evidently I'm doing it wrong. Sorry for misleading information.

[Captain75]

Doesn’t it say on your wiseco box what bore size should be?

I have bored my 90hp yamaha and waiting for Wiseco pistons. On their website is the bore size for each piston size.

Have you chamfered the cylinder ports? I read back and looked at your pictures and couldn’t see any chamfered ports. Wiseco says ports should always be chamfered. I did mine after Jennings Two Stroke Tuning Handbook with a dremel . See pic.


Do you think that the rings could had snug in the ports and caused wear in the cylinder? Just throwing out some ideas.

Hello,
I really appreciate your ideas!!
Pistons were bought fit the standard 3.685” bore. When I measure the bores I find that the wear is very small, but at the same time, Pistons seems to be a bit loose...
Just trying to establish a baseline iot decide the next move.
And yes, ports are chamfered!
//Anders

[powerabout]

how much bigger are you bores than 3.685"?
dont forget they are forged so expand more then permamold/hypereutectic stock pistons, hence seem loose when cold.
Personally wouldnt use them unless running well over 7k all day