engine build-what you think of this?

[decky]

i have a stock 26cc two bolt engine,i want to use the crank out of a 4bolt G270 racing engine as it is lighter and balanced so should spool up quicker,is this possible?

 

[46u]

i have a stock 26cc two bolt engine,i want to use the crank out of a 4bolt G270 racing engine as it is lighter and balanced so should spool up quicker,is this possible?

Do you want to know will it fit? Yes if you use the proper crank bearings but will not work with the stock CY bearings but if you go that far in to the motor should replace the bearings and seals any ways. You can use CY cranks with stock Zen bearings but you cannot use Zen crank with stock CY bearings. Most after market bearings will work with both.

You say it is lighter do you know this for fact or how did you get this information. I might be wrong but I do not think there is that much difference. When I get a Zen crank I will compare them to the CY.

I think you would do better lighten the piston or having it lightened.

 

[decky]

sorry you must have misunderstood the post,there is nothing of CY been used here,the crank is out of a ZENOAH G270 motor which is 4 bolt, how i know this crank is modified is because it is cut down lighter (when you look at them side by side) the standard one is much bigger,also before i bought this bottom end i sort of was told about it.

so i want to use A MODIFIED crank out of a zenoah G-270 **4bolt** and put it in ZENOAH 260 **two bolts** standard engine,is this possible

 

[46u]

sorry you must have misunderstood the post,there is nothing of CY been used here,the crank is out of a ZENOAH G270 motor which is 4 bolt, how i know this crank is modified is because it is cut down lighter (when you look at them side by side) the standard one is much bigger,also before i bought this bottom end i sort of was told about it.

so i want to use A MODIFIED crank out of a zenoah G-270 **4bolt** and put it in ZENOAH 260 **two bolts** standard engine,is this possible

Yes it will fit but I do not know of any different in Zen cranks but will do some checking.

 

[46u]

According to Zen web site both the Zen G260 and G270 use the same crank and have the same part number.

 

[46u]

Got this off a distributors web site.

Zenoah stock full-circle crankshaft (28mm stroke) for engines.
PMW part # 4326
Zenoah part # T2070-42001
FG part # 07313/8

Stock part on the
G230RC / G260RC
G240RC / G270RC / G290RC

Can be used on
CY23RC / CY26RC / CY27RC
GP290

 

[Sharkey]

he is wanting to use a zenoah crank that has been modified by somebody after the fact.

it will work, use zenoah bearings. however, i don't know how much you will gain from a lightened crank. it may spool faster however you are increasing crankcase volume, that will give less vacuum and in theory draw in less air/fuel. the point of the cy "stuffed" cranks is to cut down on crankcase volume to give more vacuum, and are a proven way to increase power. ive also read thats "turbo" cutting cranks can be a bad idea in a land based vehicle (but works on boats)

 

[decky]

thanks for that info sharkey,i am going to work on it now so i may take a few pics as i go aong of the cranks

i will try it anyway,who knows it may work out good

 

[46u]

Sorry need to read more carefully. Please post a couple pictures of the crank. Has any porting work been done to the engine you are building.

One time I asked Sean of OBR about stuffed cranks and he said the only difference he found on the dyno that stuffed cranks increased the torque just a very little.

I have been building Harley motors for 40 years and in my experience lighter flywheels you loose some torque. But will be interesting to find out what your findings are.

 

[decky]

46u
not been rude please read the thread,it is not stuffed at all,the crank was milled down (cut down) and made smaller all around it,much smaller,it's not stuffed.

then after cutting they need to fine tune it and balance it,in simple terms the balancing means both sides need to be the same where it was cut.

i got lazy and didn't take pics.

took leopard for a run this morning and it's a little faster but not so much it seems to spool up faster,it seems to have more torque mid range,but not a major differnce,it feels improved though but hard to see it,maybe i need to test more.

 

[46u]

Please read Sharkey post and this is where the stuffed crank came into the conversation.

 

[decky]

Please read Sharkey post and this is where the stuffed crank came into the conversation.

oh yes no probkem 46u

anyway i ran it today to be honest i can't see any major differnce,it does seem to have a much taller top end though,and a little more bite off the mark but nothing to write home about.

i feel this crank could work sweet with the correct matching of top end and bottom though

 

[46u]

Thanks for the report. If the cylinder was ported might work better like you where saying. Not real big on making the crank lighter would think running a lighten flywheel and piston would be the way to go to get it to rev faster. Lightening the crank is only making the rotating weight lighter which lightening the piston you are making the reciprocating weight lighter and I would think this would have more of an affect.

I might be wrong just going by what I have learned about balancing Harley cranks in the past 40 years but they are 4 cycle.

 

[motorman]

lightening a flywheel does not hurt torque. it improves it. and i do agree, lightening a crank seems mute to me aswell. not much to gain there, lighteneing the piston and flywheel is much more effective and easier.