crank with tins removed?

[bkstoffe]

I just opened up the cases on my ct350 pv motor, I have really nice freshly powdercoated cases to install the bottom end into.
I have a new style hotrods crank to use, but the crank that was in the motor looks like it has the tins removed? It is also a hotrods rod, so I'm guessing a hotrods crank also..
what are the pros and cons of running without tins? this crank is in good shape and I could re-use it if there is an advantage.. Any suggestions / comments or personal experience welcomed!

[85drag250r]

No tins on the crank will cause the crank case volume to increase. This will slow down the velocity (speed) of the mixture entering the transfers. Depending on what you are doing with the engine this may not necessarily be a bad thing.

[bkstoffe]

This engine is a mx port, I have everything for a trx11 port 350 pv engine also. Would I be better off to use crank with tins on mx setup with ct national and 38mm a/s and tune no tin crank on trx11 with trx11 pipe and 40.5 carb? Or would best bet be to run tins on both?

[udontknowme]

yes it will increase the volume but i dont think thats the issue here.  where the extra volume is located might be what you want to consider. with the tins gone it puts all that volume down low into the crankcase.  i would take a guess and say thats not the best place for any extra volume. most crankshafts ive seen use tins or some other kind of plastic stuffers, i believe its not to reduce the overall case volume like most people think but rather to put the volume up higher. in this pic your volume increase will be more between the red arrows section. i think you would be better off with it in the green area instead. for example if you were to put the tins back on and use a longer rod it would put your volume more in the green section. not sure what anyone else thinks but thats what makes the most sense to me anyways

[85drag250r]

Yes, volume among others things play a big role in how an engine performs. The is more to building an engine than just port durations.
An engine designed for high rpm us (like a drag engine) will tend to favor a small CCV because at high rpm the time the port is open is shorter. In a sence, it becomes harder to "fill" the cylinder with enough mixture to get the job done. A smaller CCV will increase the speed of the charge entering the transfers, this will aid in cylinder filling at high rpm. In general the more charge you can put in the cylinder, the more HP you make.
There is a down fall to a engine built for high rpm use, the engine tends to be peaky and not much fun to drive at lower rpms.
Now an engine built for MX will tend to favor a larger CCV because it will give the engine a little more flexibility. The cylinder does not need to be filled as quickly as a drag engine does.
If a cylinder gets filled to quickly, it can actually "push" the charge out the exhaust port and result in a power loss.

Now what I talk about here is just some basic "trends" in engine building. Every engine builder has their own way of building a particular style of engine.

[85drag250r]

FYI, volume inside an engine is just that...volume. It is not divided into sections.
Overall volume inside an engine is measured with the piston at TDC.

So obviously, everything under the piston at TDC is your engine volume

[bkstoffe]

Good info!  Thanks !

[udontknowme]

FYI, volume inside an engine is just that...volume. It is not divided into sections.

  if theres very little space in the lower crank area for the mixture to occupy then it has no choice but to occupy the upper area. how can it occupy a space that doesnt exist ?  with the tins in place, that extra space doesnt exist anymore

[udontknowme]

dont wanna get in a pissing match but some of the engines with the most hp per cc on planet use large case volumes and believe me its not concentrated down low in the crankshaft area

even back in the stone age when gordon jennings wrote his books he said trying to force the mixture into the cylinder with small case volumes was a thing of the past. if your pipe aint worth a shit, large case volume is probly only gonna add to your grief

people have even gone as far as to put shields just about the crankshaft wheels and tilt the reed block upward. essentually to keep as much mixture as possible out of the lower crankshaft area and let it go directly from the reed block to the transfer tunells

[85drag250r]

if theres very little space in the lower crank area for the mixture to occupy then it has no choice but to occupy the upper area. how can it occupy a space that doesnt exist ?  with the tins in place, that extra space doesnt exist anymore

By reading your previous post, you stated that "most crank shafts you have seen use tins or some other kind of stuffer, is NOT used to reduce volume but to move volume up higher"  We're are you going to put it?
Also what does putting a longer rod on the crank due for CCV?

[85drag250r]

dont wanna get in a pissing match but some of the engines with the most hp per cc on planet use large case volumes and believe me its not concentrated down low in the crankshaft area

even back in the stone age when gordon jennings wrote his books he said trying to force the mixture into the cylinder with small case volumes was a thing of the past. if your pipe aint worth a shit, large case volume is probly only gonna add to your grief

people have even gone as far as to put shields just about the crankshaft wheels and tilt the reed block upward. essentually to keep as much mixture as possible out of the lower crankshaft area and let it go directly from the reed block to the transfer tunells

How do you know that some of the baddest 2 strokes in the country use large case volumes? Did the engine builders of these engines give you exact specs?
Do you even know what a large CCV ratio is? Is a 1.5 a large or small ratio?

Please go back and reread Jennings book because you have your facts incorrect

Your last paragraph really shows your lack of knowledge

[kb250r]

Not in this guy's but just passing on what I was told in a conversation with a well know west coast pipe/engine builder on picking parts for a engine build...We were talking the tin,no tin controversy and he said  the fastest 250r in the states have crank tins and for a reason and with any engine you are trying to push every single hp out of of it",tins are a must"..But he did say that everything has its place and builder preference.I chose to go with no tins for my application because I'm not a alky balls out drag or trying  to squeeze every single stitch of hp out of a motor so mine works it just fine for me..I'm just passing on what I was told and helped me make my decision on my build..

[udontknowme]

between bell, jenning, blair and a pile of other authors its hard to keep track. my opologies it was bell not jennings who said forcing the mixture to cylinder was a thing of the past. got all them books on pdf but i dont read that stone age literature anymore so its hard to remember who said what

as time went on, knowledge of expansion chambers and 2t engines progressed which proved that small case volumes were not the way to go in high performance applications and should be common knowledge today. the cccr of a 250r i have no idea as ive never even turned a wrench on one but i would take a shot in the dark and say around the middle range of 1.4x. perhaps low 1.5x but thats just a guess. honda and other manufacturers gave their engines a volume of what they percieved as ideal given the machines intended purpose with the available knowledge at the time. to me this meens when you soup up the engine beyond what the manufacturer had it intended for, some aspects of the engine arent ideal anymore. if a person were to spend some time making a proper pipe and put a fair amount of thought into the rest of the engine im thinking there would be some benefit from a volume increase although i wouldnt remove the tins to accomplish this.

something else ive thought of several times that applies to this subject. if you take a smaller volume like what you claim a drag racer would use, and lets say it squirts the mixture quickly into the cylinder. would it not peter out and the pressure fall just as fast ? large fluctuation is what it amounts to. it seems with larger volume there would be less fluctuation and a higher average pressure enter the cylinder

[rsss396]

IMO if you are purposely adding volume to a crankcase, adding it to the lower crank area is not the best area, adding volume under the the cylinder transfer ports will shorten the path to the cylinder.
My observation is, most modern engines are are looser in the crankcase area then they were 30 years ago and pipe diameters have also increased with larger angles to help pull the mixture from the case area instead of relying on the crankcase pressure.
I think the advantage of lower velocity longer time duration of the transfer flow streams seams to be a more controlled scavenging of the cylinder's spent gases thus having a more pure mixture in the combustion chamber.