61x cylinder to sleeve mismatch

[Polish jet pilot]

hi all,

Just a few minutes ago i took off the cylinder off my 2000 engine. It has never been rebuilt and generally all parts look as they should. The crank has no play on the rods, the pistons and sleeves have justtiny bit of scoring, but superficial.

I am astonished how bad the mismatch of the sleeve windows to cylinder casting is. I heard about it, read about it, but once i took apart my first yami motor i really understand how much can be gained from porting it - or rather from actually matching the ports. .
.. Will post pictures soon so we can have alook at this..and maybe you can all chip in... Thank you

 

[WaveDemon]

DO NOT port match the top of the ports. you will ruin the low end.

 

[waxhead]

DO NOT port match the top of the ports. you will ruin the low end.

Huh where did this come from
I have found far different results

 

[kevbo]

There is a little more to porting than just matching the liner. Dont do it unless you are willing to spend a lot of time learning. A bad port job can be worse than stock.

 

[Waternut]

Do a quick search. This has been covered a few times with one thread less than a week ago. It'll probably be more info than will get posted the second time around.

 

[Polish jet pilot]

Thank you all for your input. I just wanted to share my observations and actually show that cylinder so we can compare it to other 61x and see how much can two cylinders differ (if at all). Regarding the mismatch:

I am also not sure why matching the windfows of the cylinder casting to sleeve window result in loosing the bottom end. I would not touch the sleeve windows just the casting + sport port job...?? I mean the difference in casting to sleeve window is about 3-4 mm!! Shouldn't all be aligned nicely? My kawi cylinders (550) had them aligned exactly...

 

[Waternut]

http://www.x-h2o.com/threads/65566

 

[WaveDemon]

All I'm trying to say is if you are a home hack (like me) you are far better off matching port widths than raising port hight. The miss match is not a mistake by yamaha.

 

[Polish jet pilot]

I was reading a book on 2 strokes yesterday before bed time and there were great pics showing flow inside the cylinder. Since Yami cylinder is a 5 port design it flows generally well. If you look closely there are certain angles to the casting and sleeve that direct the flow (it has to be in harmony with flow from all ports). Thus my conclusion (correct me if I am wrong here), port matching the cylinder to sleeve is OK, as long as we do not increase the heights of ports and we do not change their angles which direct flow. Making them smooth is key.

Am I right or just silly?

Andrew

 

[WaveDemon]

You are making the assumption that the mismatsh is a mistake?

 

[Polish jet pilot]

the mismatch has a regularity in itself - angles of the port windows, and these must stay the same as yamaha made them. we can keep these, but the edges, steps could be smoothened imho... Not sure but nobody really says anything - is this such a secret in the industry??

 

[SUPERTUNE]

Yamaha did a LOT of things different than their rival Kawasaki... So when you compare a Yamaha 61x 701 cylinder twin carb engine (96-up Superjet) to a SXI 750 twin carb Kawasaki (JS 750) they have very different power delivery with the Yamaha with more power down low and the Kawasaki makes more power in the mid range and top end.

If you look at the 62t cylinder that came on the 1st twin carb 701 Waveraider (I think it was the '95 model) it had more of the Kawasaki SXI powerband.

Both porting styles work well. You just have to have the matching setup for the different styles to work.
If you want to learn how a 2 stroke engine works start modifying and testing them in your application.

 

[Waternut]

The fail safe thing to do is leave the intake ports alone and do the template first. Once you've gotten a good baseline on the water and you're feeling spunky one weekend, then rip into the engine again and port the intakes and see if your power is better or worse.

Yes it requires more work. However, spending thousands of dollars and countless hours on a ski and thinking it performs great only to ride a friends ski that performs better with the same mods and no porting will piss you off and you'll hate your ski.

 

[SUPERTUNE]

Or PAY someone that's done the homework already and buy a finished product.

 

[luker]

x2

 

[Polish jet pilot]

I'd pay, if you open a branch in Europe Or if you sell "oem" cylinder style setups for few hundred bucks, not few thousand - just not in my budget as yet...a cheap entry version would sell nicely IMHO.

There are a few specialist here that deal with 2 strokes, I of them being a guy with 35 year experience in jet boats (he even has a F1 license for jetboats) and he did my previous Kawi cylinder, but I was wondering whether you had some proven recipies (which you could share) for standrad cylinder, now that everybody is moving to billet cylinders from well know builders such as Xscream or DASA, BUN, etc...

 

[Polish jet pilot]

Anyways, the first thing to do (and I bet everybody will agree) is to bring the engine to actual OEM specification (blueprinting). Gains from it are very noticeable - factotries do not make the best assemblies... then off to porting...

 

[Polish jet pilot]

I took the cylinder to that person who races 2 stroke jetboats. He looked at the oem cylinder and made a big smile. He said it is totally horrible and that everuything should be smoothend (but maintaining correct angles so the flow is kept). He also said that what I could do is take out oem sleeves and insert them lower in the cylinder. I told him this is not worth it on this setup.

 

[Matt_E]

He also said that what I could do is take out oem sleeves and insert them lower in the cylinder.

So ask your buddy what he would do to compensate for the cylinder that's now 3-4mm shorter. The piston crowns will now come above the cylinder deck at top dead center. Is he going to run special domes? Is he machining them?

 

[Waternut]

I took the cylinder to that person who races 2 stroke jetboats. He looked at the oem cylinder and made a big smile. He said it is totally horrible and that everuything should be smoothend (but maintaining correct angles so the flow is kept). He also said that what I could do is take out oem sleeves and insert them lower in the cylinder. I told him this is not worth it on this setup.

This is just my 2 cents and I'll fully admit that the guy who builds jet boat RACE (keyword race) engines knows more about engines than I do. However, some of the people who have posted here so far are also engine builders and they build jetski engines but more importantly they build/work on Yamaha jetski engines that are designed for freestyle. You might want to listen to them...or at least take the advice into consideration.

To put it into perspective a little beter. A Formula One engine builder undoubtedly knows how to squeeze every last pony out of a race engine. However, he's building an engine to run at 15,000-18,000 rpms and NOT 3,000-5,000 rpms.