my first case reed project

Both the pistons I got here at home are like the one on the left in your pics... I'll take some pics of my pistons in a little bit. I'm also interested in that Hoca piston since it uses the thinner rings.
I just partially assembled the old engine by putting the crank back in with the same jug and piston and measured the stroke, it does measure out at 40mm so it's either the rod length or the deck hight of the bottom end that's different.

Here's the pics... The last pic is just the crank on the lathe after being trued, but it still needs the pin welded before I feel safe using it...

mrfubs said:

View attachment 69683


the piston on the left is a 40mm stroke piston the middle is a 38mm and the right is a hoca that is a perfect fit for a 40mm and uses 1mm thick rings instead of 2mm thick.

if you look closely you can see my added transferport in the back ground lol

and i found another jet too

View attachment 69684

Click to expand...

That ''jet'' is an air bleed. It does affect operation but does not affect mixture much, if at all. It is a reference for intake pressure (I think)

Thanks for the link to the Hoca piston... This looks like a much better piston for a performance build and the thinner rings will help reduce friction. It does look like it's a reed valve only piston but that's also in my plans once I get a few more bugs worked out of the old engine and crank.

I thought the air bleeds were on the carb's intake horn, but I'm not fully familiar with the Dellortos yet...

Got my spacer made and it fixed my problem with the piston coming up too high, I made the spacer out of 040" thick 7075 T6 aluminum and it sets my port timing at some really good numbers.. for the most part... (the intake duration could be better, but an easy fix)
With my indexed piston the numbers are as follows...
Exhaust port opens at 105 degrees, giving a duration of 150 degrees
Intake opens at 78 degrees for a duration of 112 degrees
Transfers open at 120 degrees for a 120degree duration
I'm happy with the transfer and exhaust durations but the intake I would like to bring up closer to 125 degrees duration to better match the transfer and exhaust durations, it'll run like this but may be too short on duration restricting top end power and usable rpm. I can raise the bottom of the piston skirt a little more to correct this and it'll be ready to assemble and put on the bike for some testing.

They're the port timings I get when I raise a 38mm stroke barrel by 1mm and use a 40mm crank, your on the right track. get your inlet to around 60 and you will have a nice running motor, you sure your other crank is a 40mm?
the high gudgeon piston does not only come with 38mm crank.
its the rod that makes the difference to which piston you run.
you can have 40mm with high or low gudgeon and 38mm with high or low gudgeon.
PK80 or F80 has 40mm low gudgeon.
GT5 has 38mm high Gudgeon.
Super rat? has 40mm high gudgeon.
and there is a 38mm with low gudgeon, A80?
You can clearly see the difference in the big end pin position when you put the 38 and 40 side by side.

That's some new info for me, I thought all the 40mm engines used the low gudgeon and the 38's all used the high gudgeon to compensate for the shorter or longer stroke length. I went back to the ebay ad that I bought my original engine from and he's calling it a PK80 on the ad title, but on the spec list at the bottom of the page he calls it a T80... I never noticed that until I just looked at the ad again, but I'm assuming the engine is the same as the PK as far as the bore and stroke goes and the basic setup etc... I did double check and measure the stroke on this engine just to be sure and it did measure 40mm so both cranks are the same stroke.

Anyway, I'm kinda chalking this up like the variations in the rotor clocking and cylinder port shapes etc... My assumption is that model has a higher base deck hight, it could be a shorter rod, but to measure teh rod accurately within 1mm with it still mounted on the crank would prove difficult, and I really can't see why they would use a different length rod, but on the other hand I've noticed some sellers make it a point to say the rod is the 110mm length.

Thanks for the extra info on these engine specs... I knew the difference between the GT5 and the PK, but not the Super Rat and the A80 etc... I knew the Super Rat had some differences in the magneto and ignition system as well as a few more subtle differences... but even looking at these 2 engines I got side by side, there are quite a few differences both inside and outside.

all 5 motors I have, have been different.

1st. RSE F80. 40mm 5 piece crank, low gudgeon/short rod, straight fire head. Got this motor 2nd hand, and have had it doing 80Km/hr at 9500RPM, It was doi'n about 50 odd K/hr when I first got it going, but has had many different states of tune since.

No 2. A80?, 38mm bushed big end 3 piece with low gudgeon and wide inlet but not big ports?, short straight inlet? this crank was never run, the motor was torn down for parts, the cases have a wide mouth and fit my Alloy Framed Goat, with an RSE crank (low gudgeon).

No 3. 2nd A80? Gt5 'style 38mm stroke long rod/ high gudgen. this was also parted out, but the crank was crap, infact the whole motor kit was crap, the cases went to the old RSE crank, now in the Soft tail.

4th motor, I new I was after a 40mm crank, but didn't notice when I bought it, but it had a 45mm piston? so 'bored it out' with a new piston and jug, that's in the Phantom and is a sweet motor now after it's de tune, it went great before, but would get too hot for the angle fire head.

5th motor, which is my case induced project, I got a 40mm stroke, large port jug (but with narrow inlet studs?) that was unusable for porosity bubbles. and a long rod/ high gudgeon piston? Still this piston looks to maybe give better flow from piston to transfer port?
But it seems the high gudgeon piston may be hard to find in OZ, but I have one new and one used piston here to experiment with.
So have been considering getting another RSE crank? for it's better potential primary compression and shorter rod.
Have been doing a bit of contemplating on my new cases, and have decided to build the cases up either side of the reed opening to get a flat surface to mout the reed housing to.
I want to get my reeds as close to the crank as possible, but am worried they wont be able to open wide enough.

And Dave your 105 exhaust and 120 transfer timing is what I run, with a little over 60 on the inlet.
It probably does make the motor a little 'peaky', but works well with a good pipe! you will be getting max power from 5000 to 8000.
I have lifted the exhaust to around 102 and transfers to 118 and they still run great, with a little low end sacrifice, but 6 to 9500 happy as.

Nice... When I had it running before with that timing it really liked it and you could definitely feel the power kick in once the revs got up... mine started 4 stroking at higher rpm's but that's easy to remedy with proper jetting, and I got that Rocket CDI I need to test out as well... I did open up the CDI and tool Lots of high res pics of it before sealing it better and heat shrinking it to protect it from the elements... and look better

I also got a few different type reed valves to experiment with once I get all the bugs worked out of the older bottom end I got apart right now too.... Looks like the one that I got for a large RC model engine might be the best one to use since it's pretty compact with 4 petals but can support up to about a 21mm carb

I'd say this 4 petal RSE reed I have is RC based.
And would have been designed for the Walbro similar to my Tilly. (WJ71?)
And I'd say 21mm would be it's absolute max, but I'll only be running 16mm with it.
My 4 petal pocketbike reed is much bigger, and should easy flow enough for the Tilly.

I'm thinking the RSE reed is the smaller version of the one I got, the RSE looks a lot like the OS 50cc reed valve...

The width of my reeds are very similar, but the length I imagine should let them open wider. But I was thinking another set of RSE reeds might be an easy way to do this.

I bought 4 or 5 different reed valves so I could have them here in my hands to experiment with and the one I've been leaning the most toward using is the DLE reed, which just so happens to be the same reed RSE uses for their kits and it's the one in Theon's pics above, I left pics on his thread of the other possible reeds... The DLE reed is actually for a large RC model engine, a 60cc twin cylinder aircraft engine... I'd even like to put one of these engines on a bike since they're both powerful and compact...

The lathe in the pic is a Harbor Freight 7x10" mini lathe and it's been a real work horse for me. I wasn't sure how much I'd use it when I bought it, but I've ended up using it for one thing or the other almost on a daily basis ever since I got it home and set up. The beauty of this little machine is it's small, weighs about 80 lb, and there's all kinds of accessories and upgrades for it... it's kinda like the small block chevy of the hobby size lathes. I can even do some limited milling with it. One thing about these tho is you do have to true everything up on them before they'll cut accurately but that only takes about an hour... it took me longer to get all the preservative grease off it than it took me to get it trued up... lol... There's all kinds of goodies for it at http://www.littlemachineshop.com/default.php so these things can be seriously upgraded too

Check out Theon's post on his bike builds for my pics of the reed valves, or I can post them in here too...

That's what I was thinking on the Hoca piston, the port window is too big to reverse, and some of the higher quality pistons may also be slightly off round so they'll be round after heat expansion from the exhaust etc... I'll need a good piston when I case induce my old case, but I'll run the stock pistons for now with the piston port setup, they're cheap and easy to cut on etc, the main thing I don't like is the fat 2mm rings, but I've run them with just the top ring and they did ok.

Quick correction on my reed valve... it's from the OS GT60 RC engine, not the DLE that I mentioned earlier, these are the same reeds RSE uses in their reed valve kit... Here's the ebay link to the one I got... http://www.ebay.com/itm/360884633562?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

And here's the reed valves I bought for experimenting, one is off my old pocket bike, the funky shaped one is from a chainsaw, then the OS reed, and the last one is from a Yamaha Jog...