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Post by Thebatman on Oct 15, 2011 14:11:16 GMT -5
Hello guys. I have a few choices and questions to throw your way for some input.... I had a 47mm bbk (malossi)with the stock crank and it came out to be a 71.8cc..(my kymco zx build) I am wanting to rebuild my baby and i am torn. I HAVE to have a new crank regardless. 1). My dilemna is either the oem 41.4 stroke with a 70-72cc bbk(47-48mm). To make a 71.8 again. 2). Or try a 44mm "baby srtoker crank in the 47-48mm bbk which takes me to 75.8 but what would the 44 do to my port durations/timings is my fear?   3). OR get a 50mm bbk from jiangwayne(on sale,uses studs not bolts) With a 44mm crank. Which should bring me to 83 The timings should be"there" with a 44 instead of oem crank with this kit SURELY(oem be to small i'd think). The price difference for either route is like $50 for 11 extra cc's.. 4). Which brings me to this point. I am leaning toward the 50mm/44mm(i like 11cc's for $50 too  ) BUT i am running the LV ZX exhaust. Would this pipe take a 83cc or fall? If the pipe would be worthless, then i'd probably have to stick with the oem crank on a 70 bbk 5). Who, if anybody has used a jiangwayne bbk.(they are suppose to be good quality stuff from what i read)... Also the other kit can come from carlos, BUT i have heard mixed emotions about his bbk's....jiangwayne or carlos for the kit? I also need to throw in "Ruima" brand in the list of bbk's. Has anyone ever used that brand? 6). Would the longevity,etc. suffer alot worse being 50mm instead of 48mm, Or is it ABOVE 50mm it weakens alot more? Thanks guys for some input on this "plan" i have going on for cranks and bbks....again... :no: |
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Post by 90GTVert on Oct 15, 2011 17:11:03 GMT -5
The 44mm crank will make the transfer durations pretty long on a cylinder meant for stock stroke. Not sure exactly how bad. Might still be OK? I'd go for a cylinder that matches up to the crank.
Measure the stinger length and diameter on the ZX. All 50-70cc pipes aren't built the same and some might work with the 83cc.
I've never paid much attention to stuff for other engine platforms, but most of the generic stuff for minarellis tends to be pretty similar. I have a Ruima kit or had (again, a lot are very similar). Seemed about the same as the no-name stuff to me.
You'd probably be fine with whatever bore size. I dunno anything about your platform really, but I do know there are some big ass strokers out there. If you've seen the 50mm+ thread here regarding engine failure, that's about the GY6 50cc engines.
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Post by reveeen on Oct 15, 2011 18:13:20 GMT -5
I'd be really careful of the jiangwayne stuff. I have a 54mm cylinder here paired with a 44mm crank, and the port timings are, well, not for the faint of heart (225 degrees exhaust, 160 degrees of transfer). I'm just juggling things now to try and get some kind of compression. The "ideal" is to match your pipe to your port timings. Brent has put up a chart towards the bottom of this page: 49ccscoot.proboards.com/index.cgi?board=yamajog&action=display&thread=1712&page=2That gives you the relationship between port timings and the rpm the power will be generated at.......... you would typically buy a pipe that "works" @ the rpm/power point, but because you already own a pipe you would work it backwards.......... setting your port timings to match your pipe. |
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Post by Thebatman on Oct 15, 2011 19:21:12 GMT -5
I'd be really careful of the jiangwayne stuff. I have a 54mm cylinder here paired with a 44mm crank, and the port timings are, well, not for the faint of heart (225 degrees exhaust, 160 degrees of transfer). I'm just juggling things now to try and get some kind of compression. Read more: 49ccscoot.proboards.com/index.cgi?board=genchat&action=post&thread=2769&page=1#ixzz1atm6rzYU@ reveen.. I seen that same kit you have. I seen where it says to use a 52.6mm crank witha 54mm kit. Maybe that's the issue your having?? I was under the impression that they actually tested the products,etc. before. But of course any and all input is greatly appreciated... Thanks guys for the replys.. I have read where some ppl say that studs are better than bolts like i used last time for the head. I know of 1 guy "down under" that did a 50mm kit with the oem crank and had a HELL OFA time with durations. Now he's running a 47mm with a 44 crank and seemed to have some sucsess but always having fits. That's why i thought of the 50mm kit with a 44 crank. That SHOULD make it a83cc.. A lil baby size stroker... ;D This time i will have my 7" extension installed.  I found a "ruima"47mm at a good price.. Carlos has a 48mm at a good price. I do believe if i STROKED it to a 120+cc, then i'd definately need rebuilding every few thousand miles... I'm sure anyway. But a 70-72 will last Would a 83 be comparable to that?..I can save $50 and lose 11cc's but if in the end if it's not worth 11cc's. I can't lie, of course i love the idea of a 83cc and no machining is involved!! can use stock seals/bearings technically... :laugh: |
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Post by Thebatman on Oct 15, 2011 19:44:21 GMT -5
Would the target timing numbers still be the same with building a 83cc as they are for the 50-70cc builds?
Or would you want more aggressive numbers?..( i had on the zx build 182-185 ex...128-130 trans...126-128 boost)
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Post by reveeen on Oct 16, 2011 1:16:40 GMT -5
I seen where it says to use a 52.6mm crank with a 54mm kit.
When I bought the kit "the story" was 44mm. or bigger.
It is really ok, as in: I can live with it, if you ever had "doings" with a high horsepower 2 cycle dirt bike, the scooter engine turns over just the same. (nothing on the kick starter for most of it's stroke)
The port timing chart I linked you to is a guideline, not an absolute, but roughly the numbers stay the same no matter the physical size of the motor.
You are in Honda territory now. If mild is your desire, using a 44mm crank, a NH80 cylinder bored to 50mm, and a Wiseco piston, you will get your size. A NH125 cylinder will go on there, though the port timings will get a bit radical, once you have shaved the deck to match a 44mm crank.
I *suspect*, with a 44mm crank, the CR80/85 stuff (cylinder/head) will fit.
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Post by Thebatman on Oct 17, 2011 6:54:22 GMT -5
Well guys, i got some answers back from them but now i'm conserned about the LV ZX exhaust i have... Would this exhaust handle 80-83cc or will it be dead in the water? ? I would like to do the 50 witha 44 crank and go up to 80-83cc instead of the 72cc i did have? So i guess my exhaust is worrying me And if a 44 crank would destroy the timing on a 48 kit |
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Post by reveeen on Oct 18, 2011 5:03:41 GMT -5
I would not worry about your exhaust until you manage to get over 90cc...... There is another consideration though (that I can't help you with, because I don't know) it seems that there are several exhaust outlet angles, so you may buy a cylinder and find your exhaust doesn't fit. So, it becomes a matter of the outlet flange angle, and the pipe diameter....... seems to me that the 50mm (and under cylinders) are 25-26mm exhaust outlet diameter.
If you end up with too short a cylinder you will have to make yourself a stroker block (or plate). Moving the cylinder upwards with a block, or plate, will increase your timing durations. Probably the safest route is to buy a cylinder designed to work with a 44mm crank. I can measure the height of cylinder you need if that is any help?
I have a NH80 cylinder here, 73.05mm high, stock porting, that will work with a 44mm crank. For a piston you want a 1983 CR80R (Wiseco #493) in your desired bore size (49.5-51.5mm).
1) the cylinder needs bored
2) the cylinder has been repaired @ the exhaust flange, but is useable
3) the stock porting is VERY MILD, making peak power around 5000rpm.
You can have it for shipping.
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