5 mm strokers

[eel]

What are people running, cylinder wise?

 

[Mike Serlin]

art at jetworks makes a mean and affordable 4 mil stroker that I've been hearing good things about.

 

[sjetrider]

You should be able to run a 5 mill w/ flat top Kawi pistons and a thicker base gasket. Otherwise a 5 mill plate is required at base of cylender.

 

[D-Roc]

Team Scream builds an amazingly powerful 5mil on a 61x cylinder, the pistons stick above the cylinder so he cuts the domes and who knows what else he does to these motors of his but the end result is true smooth delivery of high hp!

 

[#ZERO]

I'm building a 62T/61X flat top 5mm stroker right now and I'm using the Northwest sleeves #1588-BB because the transfer port timing is about 2mm lower then stock and it has a 16.4mm window opening for stroker use. The exhaust port is about the same height as the 61x sleeve which should give me some great bottom end. The only problem is that I'm going to have to mill the cylinder bottom, cut the sleeve length and machine the domes to obtain the correct port timing for freestyle use.

If you're going with a 5mm crank re-sleeving is a must or the only other way this would work is to purchase a Lamey or ADA cylinder and they're just a bit more then I want to spend right now on something that I'll probably end up blowing into pieces anyway.

Here are the measurements taken with the engine on a degree wheel with the sleeve at different heights.

88° Exhaust Port Opens
117° Transfer Port Opens
184° Exhaust Port Duration
126° Transfer Port Duration
29° Blow Down

89° Exhaust Port Opens
118° Transfer Port Opens
182° Exhaust Port Duration
124° Transfer Port Duration
29° Blow Down

90° Exhaust Port Opens
119° Transfer Port Opens
180° Exhaust Port Duration
122° Transfer Port Duration
29° Blow Down

 

[Watty]

Dude!

 

[eel]

#0.

I was looking at the port map, are you sure about the 58.2 transfer height with an 8.88 top flange? I'm measuring approx 58.2 to get the sleeve to align with the stock mismatch with stock 3.5mm flange.


How wide is the ex. at the widest point?

The ex. roof looks scary flat. Have you had issues before?

cheers, eel.

 

[#ZERO]

Yes… the measurements were taken from the outside of the sleeve with a digital micrometer. These sleeves are very well made with steep roof angles on the transfer ports that go all the way through. They will almost line up with the transfer port roof angles on an un-port 61x cylinder. The measurement taken from the inside of the a brand new sleeve is 57.3mm and as you increase the bore size the transfer ports top deck height will be lower each time. They were made mainly for flat top pistons because they are 3.88mm lower then the oem Yamaha dome pistons. The 8.88mm or .350" top flange is there so you can install the sleeves at different heights to change your port timing and to keep the sleeves from developing cracks as the bore size increases. The exhaust port roof has a very nice contour to them and if you want to see scary flat take a look at the big bore LA sleeves. You can run them flat across the top but you have to chamfer the ports real well and they should not be more then 66% of the bore size for freestyle calculated from a value to a value. Here's the port timing map for the Northwest sleeve exhaust side and a picture of the LA big bore sleeves exhaust port with a map. The Northwest sleeves will work great with a 5mm stroker with dome top or flat top pistons. If dome top pistons are used you have to install a 1mm ~ 2mm base plate under the cylinder and if flat top pistons are used you need to machine the bottom of the cylinder about .090" ~ .140" to get your desired port timing, duration and blow down.