Con rod lengths, how many different ones are there for chinas?

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tormentandglory

tormentandglory

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Does anybody know how many different conrod lengths are in china motors?

I'm starting work on a new project engine, I'm gonna run a 110 3v crank (49.5mm) in a yx150 with a lifan 150 oil filter clutch cover. The finished engine will be a very rev-happy 140cc's.

I need to find the longest possible conrod so I don't have to machine the crap out of the cylinder. I have an atomik 150cc crank (59.5mm) and a jialing 3v crank lying around. The 3v rod is a bit shorter. I haven't actually measured them centre-to-centre yet.

Has anybody played with different rod lengths? Any recommendations or suggestions?
 
not to sure how many rod sizes are out there for the chinas
but you can change the deck hight of the piston that should get it to the end if the cylinder
 
I'd have to machine almost 10mm off the cylinder. The piston I want to use is shorter, the crank has 10mm less stroke and the rod is shorter. I can swap the rods over, that gives me an extra 2mm or so. Not nearly enoguh.
 
you will need do more than shorten the chain
and make some sort of cam gear adjustment
also you can get stroker pins from akunar i think there available in 1mm- 6mm
and you take the pin ofset size and double it and that gives you the extra stroke you will gain
 
Yeah, I run slotted cam gears in all my motors. Standard china cam timing is always wrong whether you've machined stuff or not. An offset pin will give me more stroke, thats not what I want. I'm trying to build a short stroke motor...
 
Kurlon of Planet Minis did a thread on rod lengths and maybe rod ratios ... You need to work out what length rod you need ... then look for a piston pin height/rod length combo to suit your application ...

I think AKUNAR might know about OR even have rods in various lengths ... or maybe a rod out of a vertical Jap engine might work ... if the big end bearing sizes are bigger you could cylindrically grind the ends of the Jap crank pin down to fit the chinese crank halves ... or bore the crank halves out to suit the bigger pin ... Remember ... IF the new rod / pin / bearing / piston set up is heavier than the stock 110 3 valve parts you'll have to re-balance the entire assembly ... or suffer the consequences ...

Then there's a custom made Titanium billet rod ... LOL ... (ARGO ~ CARILLO ~ CROWER ~ CHILDS & ALBERT etc etc )

Powroll used to heat the rod beam and compress the rod shorter in a jig ... maybe you could try STRETCHING a rod ... but I don't like the idea personally ... He he he ...

Kurlon talks about building short rod engines which would be OK for dirt bikes where you're "on the throttle and off the throttle" all the time ... but long rod engines are better for speedway , flat track , drag racing , road racing and any other sustained high rpm usage ...

There's some really good rod length info in this car forum thread ...

long rod short piston vs short rod long piston - LS1TECH
 
I've decided to use the lifan 150 rod, its a few mm longer than the 110 rod. I could fart about chasing more, but I'm too lazy. I was hoping other people had played the rod game before.
 
mmmm, my two cents worth...

i never frigged around with changing rods themselves, but i do have a "lifan" ip52 that has a cylinder thats 10mm longer than any other "52" type engine ive looked at(80mm versus 70mm). and logically, the rods 10mm longer cus the stroke is still the same and the piston comes all the way to the top... nice for the high revs on the highway, i believe :)

i havent gotten up close and personal to a sachs yet, but from what ive seen, they look to be the same engine... another so called "lifan" that isnt...
 
The Sachs "Madass" engine is supposed to be a 125 Lifan ... I checked one out at a local shop and the engines do look like Lifans ... but specially made for the scooters as they have a pollution pipe coming out ouf the BVH plus an electric starter on top ...

I just measured a Genuine Lifan 125 cylinder and they're 78.2 mm (bare cylinder of vertical finned start in gear "Super" motor) ... Our 120 Loncin cylinder (vertical fins) measures 78.7 mm ...

Firepower357 on Planet Minis will know what rod lengths you can get T&G ...
 
Just in case anyone besides me is interested... I stripped 3 cranks to make one for my next engine project, and I found that the atomik/yx 150, that looks like a lifan 150, has a conrod 3.6mm longer than a 110 3v engine. The 3v rod is the same length as a yx 160 rod. I have a shiny new yx 4 valve head and 62mm cylinder kit here. Using the 110 crank will give me a very rev-happy 150cc. Check out the for sale section to, I'm selling a couple of 67mm bbk's for yx engines, mega big cc's to be had!
 
All good info mate ! ... What's your opinion on the quality and finish of the YX 4V head ? Are the ports OK or do they need some clean up , blending and smoothing work out of the box ? ...
 
quality of the 4v head is excellent. The ports are a bit on the small side. I'll stick the grinder in there and fix that up. Chamber will also benefit from a bit of careful adjustment. The piston is beautiful. And the cylinder looks nice to. Apparently its all made in taiwan, not mainland china. I'm quite impressed, so i'll be getting more very soon and selling them if anyone is interested...
 
well...from my experience with this yx4v...
its everything else then the casting and the ports that failed on that head...it was the valveguides and the rocker arms that couldn't hold the high rpm's... the shims were flying everywhere..this heads rev like crazy and they build up heat like crazy too...and the cams...ooh Boy the cams..:rolleyes:

Iam not soooo happy about all this 4V craze lately , because I am the one, who has to try to fix it, if something goes wrong here...but the kids wreck my nerves about this damn heads:mad:
 
My new crank is nearly finished. I'll take it to the bike shop tomorrow and get it trued up properly, I don't have any V-blocks to do it myself. Its a 110 3V crank, machined on the end to suit a slingless oilfilter type clutch cover. It has a longer rod from an atomik yx150 (not the klx style motor). I also made bushes so I can fit the bigger yx160 main bearings. You can see em in the pic if you look closely. Most chinas have 20mm/52mm bearings, but the yx150/160 have 22mm/56mm bearings. 140cc on a 49.5mm stroke with a heavily ported dirtmax head, should be a screamer!
 
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tormentandglory said:
My new crank is nearly finished. I'll take it to the bike shop tomorrow and get it trued up properly, I don't have any V-blocks to do it myself. Its a 110 3V crank, machined on the end to suit a slingless oilfilter type clutch cover. It has a longer rod from an atomik yx150 (not the klx style motor). I also made bushes so I can fit the bigger yx160 main bearings. You can see em in the pic if you look closely. Most chinas have 20mm/52mm bearings, but the yx150/160 have 22mm/56mm bearings. 140cc on a 49.5mm stroke with a heavily ported dirtmax head, should be a screamer!
Click to expand...

may i ask why you didnt just use the yx150 dt-5 crank instead of modifying one.
or was the stroke too much for you...
 
The whole purpose of this build is the short stroke. Its still a big engine but it should be heaps easier/safer to start and have a much nicer power delivery.

I don't like the vicious torque my 150cc engine has. The throttle is like an on-off switch, very hard to ride smoothly. That engine runs a bore and stroke of 56mm x 59.5mm.

And I'll be able to run an oil filter now to :)
 
so wat did the conrod ratio end up being?...

long rod engines produce more torque and promote pinging due to being at TDC longer
 
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