i was wanting to add that bikeberry has picctures of pistons with dimensions included. they could start off a real good thread of known parts plus a little added info.
Curious about the engine, :question:
- Thread starter mapbike
- Start date
i was wanting to add that bikeberry has picctures of pistons with dimensions included. they could start off a real good thread of known parts plus a little added info.
yes, I do that on all my engines since I havent had one yet that didnt need it even when only one base gasket is used.
This one I got off ebay last year by a seller named lalexander711 ... The listing isn't there anymore but he sells a lot of scooter parts etc.
so im wondering if you may have a half breed type or could it be a 40mm stroke engine....hmmmmm????
meassuring where a piston is at tdc using a type A piston and jug seems to be the best test of whether its a Mongrel engine or not.
I'll do a few more checks when I get back to the shop tomorrow if things are slow enough in the morning... I just got the jug off and the bottom end temporarily put together, and got a piece of aluminum bar stock with an old roller bearing for doing my mock ups with the wrist pin and piston... I also got that titanium wrist pin and bronze bushing I can use for a more accurate mock up install... I don't trust to run it with that pin in there anyway, and the pin and bushing do come out a tad heavier than my steel pin and needle roller bearing. Once I take the rest of the measurements I'm going to pull out the crank and work on cutting a hole in the case for a case inducted reed setup.
Oh yeah... that rod with the CY cast on the side... so far that's the first one I've seen with that. The rod in this one is also bare and it's not copper plated like most of them. I'd also like to try and measure the rod length since it definitely seems a little different I remember the piston was flush with the deck with my old jug installed, but when I put the same jug on the Dax lower, the piston stuck out about 1mm and I treid both pistons with the same result.
Rod length is important. Most of the 38mm cranks(excluding the GT5) seem to have 110mm rods. This puts the piston about 1.5mm in the hole. If you had the 114mm rod then it would be about 2.5mm+- out of the jug using no base gasket and less with one, probably about 1mm or so. If your rod is 114mm then you need the high pin piston. Im curious where my piston will be when I assemble my engine. Im betting at the top of the jug. However there is a curious machined ring(to small to be a squish) in the head maybe for piston clearance. This may account for why some engines arrive with multiple head gaskets.
Who knows!
Another thing this engine has the nicest head gasket I have seen. It is precisely cut not to expand into the cylinder. Im betting the piston has some pop up. In fact everything about this engine is 1st rate in manufacture, even the gaskets are excellent. If it has pop up then its gotta have higher compression than a standard 40mm.
Also I have not paid much attention to the angle of the intake ports on the jugs. This one appears to have a deep angle like the port is lower?
Who knows!
Another thing this engine has the nicest head gasket I have seen. It is precisely cut not to expand into the cylinder. Im betting the piston has some pop up. In fact everything about this engine is 1st rate in manufacture, even the gaskets are excellent. If it has pop up then its gotta have higher compression than a standard 40mm.
Also I have not paid much attention to the angle of the intake ports on the jugs. This one appears to have a deep angle like the port is lower?
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From what I can see there that jug looks fairly clean cb2, curious to see what you wind up with.
Ok heres the 38mm/114mm crank/rod with the high pin piston. Yall tell me if the piston is higher than the half breed. Its at the top of the cylinder bore. Theres a chamfer ring above the bore, the piston is below the deck. This appears to be a purpose designed low compression engine? Look at the piston at BDC and TDC. Yall tell me what you see. Also there is a good bit of side to side play in the crank, and the gaskets not even in yet.
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Yes it sits higher than piston in my half breed engine does.
I made a couple voids today showing some different jugs I have on the gt5 and on one of the 40mm stroke sax lowers.
Ill try to get them uploaded as soon as I can and ill post Youtube links here.
I don't know how they turned out yet so hopefully the focus is good, if not I may have to make them again.
I promised some port pics of the Song Top engine a few days ago......
Business got brisk and I forgot.
Then I stuck the engine in a bike...... Dugh sorry.
BUT I did remember yesterday to take a few....
I didn't get any of the crank though .
It was true though and a well polish'd unit. No perceptible side play.
Fired the engine last night. Smooth as silk.
I did have to ( every one should always ) replace the head studs and nuts .
As , out of the box the engine had no head gasket seal.
Business got brisk and I forgot.
Then I stuck the engine in a bike...... Dugh sorry.
BUT I did remember yesterday to take a few....
I didn't get any of the crank though .
It was true though and a well polish'd unit. No perceptible side play.
Fired the engine last night. Smooth as silk.
I did have to ( every one should always ) replace the head studs and nuts .
As , out of the box the engine had no head gasket seal.
Those transfers look good boxcar, looks like the jug has the rectangular ports instead of the small cat-eye looking ports.
I still need to make the video I spoke of making that shows ports in relation to the piston when its at BDC, I made one but it didn't turn out like I wanted and it was just to dang long.
Your pics give a good view of how much the transfers are opened at BDC of the piston, this is something I was curious about since out of all the new jugs i have only two of them will open the ports that much at BDC of either the 40mm stroke GenIV lower or the GT5 lower I have, I'm starting to see now more than ever that all china girl cylinders aren't made even close to equal, it's looking to me that most of the run of the mill cylinders available on-line have small transfers and they are to low, some of mine are only opened half way at BDC one either the 40mm stroke engine or the 38mm stroke engine, a couple of them open just barely over half way.
I'm becoming to realize now why the performance between different engines can be so different, even though they both may have basically the same mods.
Seems that maybe the engines with the lower smaller transfers are good for lower RPM set ups that are built to have good low end and a little mid range power that will get a bike geared right into the mid 30mph range, but even with all the other correct mods those engines just wont ever accomplish mid to upper 40mph speeds.
looks like you may have a good one there boxcar, if that engine is silky smooth like you say and because it has such good looking ports, I'm gonna say you have an engine there that has some good potential for a mid to upper 40 mph cruiser with the right gearing, carb tune and exhaust.
Thanks for sharing the pix boxcar.
I still need to make the video I spoke of making that shows ports in relation to the piston when its at BDC, I made one but it didn't turn out like I wanted and it was just to dang long.
Your pics give a good view of how much the transfers are opened at BDC of the piston, this is something I was curious about since out of all the new jugs i have only two of them will open the ports that much at BDC of either the 40mm stroke GenIV lower or the GT5 lower I have, I'm starting to see now more than ever that all china girl cylinders aren't made even close to equal, it's looking to me that most of the run of the mill cylinders available on-line have small transfers and they are to low, some of mine are only opened half way at BDC one either the 40mm stroke engine or the 38mm stroke engine, a couple of them open just barely over half way.
I'm becoming to realize now why the performance between different engines can be so different, even though they both may have basically the same mods.
Seems that maybe the engines with the lower smaller transfers are good for lower RPM set ups that are built to have good low end and a little mid range power that will get a bike geared right into the mid 30mph range, but even with all the other correct mods those engines just wont ever accomplish mid to upper 40mph speeds.
looks like you may have a good one there boxcar, if that engine is silky smooth like you say and because it has such good looking ports, I'm gonna say you have an engine there that has some good potential for a mid to upper 40 mph cruiser with the right gearing, carb tune and exhaust.
Thanks for sharing the pix boxcar.
Hey Map low transfers aint all bad they give a higher compression ratio. You can ramp the pistons a bit and or stuff the cases.
yeah I have done the piston ramping and it has worked good for me.
thing about some of the jugs I have here is that the ports are very small to start with and then @ BDC they're only half open, I just figured the small ports with only being half open @ BDC was going to really limit the engine for high rpm potential.
The other jug I have that has the larger re tangular ports that are about 90% open @ BDC seem to me is the best choice for a high rpm build that will handle the extra fuel/air mix from a carb like the 20mm Mikuni I recently bought to use in the future.
so far none of the engines I've put the low tranfer port jugs on will rev nearly as high or pull as hard on top end as the larger port jugs with ports that allow a larger fuel/air charge to enter becorw compression.
You may have hit the nail on he head though with case stuffing, that may be the se ret to getting primary case compression up to force a big charge through even the smaller lower ports.
Im in no way an expert on 2 smokers and have a lot to learn, but I just kinda go with what I've already done and what has worked best for me so far.
It is possible though that I could be doing some things that aren't exactly right and robbing myself of some power, but honestly Im not looking to have 60mph bikes, I've hit 52mph on one of them and that was fast enough for me on my lower end bikes, I really just look to get 43-45 mph top speed and a good ruise speed in the mid to upper 30,s that is fairly reliable and Im happy.
Im not one to get super deep into some of it because honestly I just dont have the time or the patience for it, I just want a smooth as possible running cruiser that will allow me to zip with the tracfic in town on the 40-45mph speed zones now and then and also be able to cruise along nicely in the 30-35mph zones and Im a happy camper.
Thanks for the advice though I do appreciate it.
Map
Yeah you are right about the low transfers/ramped piston not helping top end it really adds to the bottom/mid range. Stuffing is like super /turbo charging, intake tracts are not of too much concern since it get rammed thru.
My conclusions are be careful buying parts. With the turn over of engines/parts inventories you may or may not get whats advertised. I don't think web pages are always change when the inventory does. One supplier just updated his page. What was indicated was not what was received.
My take away on the crank/rod/piston discussion is that the GT5 type engine with the 114mm rod is made to be a true 38mm engine, as the piston reaches the top of the cylinder. What the porting is I cant say as Im not a high-pro guy. The rest of the 38mm cranks with the 110 rod make the 1/2 breed and will require a lot of jug work. And there is the 40mm crank which is what I think that most of the jugs were designed for. My FH engine is 40mm.
So once again as always it sort of a crap shoot as to what you will really wind up with. If you are not able to radically machine a jug, I would say either a GT5 engine or an engine with a verified 40mm stroke is the way to go. Problem is finding folks that really know what they have.
My take away on the crank/rod/piston discussion is that the GT5 type engine with the 114mm rod is made to be a true 38mm engine, as the piston reaches the top of the cylinder. What the porting is I cant say as Im not a high-pro guy. The rest of the 38mm cranks with the 110 rod make the 1/2 breed and will require a lot of jug work. And there is the 40mm crank which is what I think that most of the jugs were designed for. My FH engine is 40mm.
So once again as always it sort of a crap shoot as to what you will really wind up with. If you are not able to radically machine a jug, I would say either a GT5 engine or an engine with a verified 40mm stroke is the way to go. Problem is finding folks that really know what they have.
Ditto...100%
I agree that the GT5 and a confirmed 40mm stroke engine is the way to go if possible for anyone who doesn't have a way to do some machining.
Im seeing that the engines with superior port timing seem to be the 40mm stroke engines, the GT5 seems to be better than the "half breed" geometry.
I do think for the person who just likes putting around in the 25-28 mph range will do just fine with any of the engines discussed here, some a bit better better maybe since one of two exact engines may actually perform better, this is where the "crap shoot factor" comes into play.
I will post some pix here today that I took last night showing the GT5 lower I have with 4 different jugs I have on it, the transfer ports are all I focused on in the pix.