Author Topic: Crank tins....will rebuilding a crank, removing tins to true create a hp loss? (Read 10503 times)

Mr250sx · « **on:** January 06, 2014, 02:31:56 PM »

Just want some honest opinions from the drag guys on this. I have a crank to rebuild and the local machinist/engine builders say on our Honda cranks the only real way to true them perfectly is to remove the tins. I asked about changing crankcase volumes due to removing them and causing changes to velocity and flow effecting performance and possibly causing a loss and they say that there's no way you would ever tell the difference and they could hide a motor without tins in with others and you wouldn't be able to pick it out of the bunch. Is this true or should I steer clear of this option? I'd like to know whatever info there is out there. Thanks

jcs003 · « **Reply #1 on:** January 06, 2014, 03:18:28 PM »

http://www.youtube.com/watch?v=XQEGPmA9HUY

john

Pumashine · « **Reply #2 on:** January 06, 2014, 03:19:23 PM »

Yes, the tins are removed to do the rebuild and put back on after finishing. Obviously they have not done it before.

C-Leigh Racing · « **Reply #3 on:** January 06, 2014, 03:24:40 PM »

One thing for sure, with the tins removed, you'll never have to worrie about them slinging off & destroying the engine.
You'll loose quite a bit of case stuffing with the tins removed from the crank, but there are things you can do that will close the case volume back up.

A big bore cylinder, like 350cc & larger, will displace some of the gained case volume from the tins being removed, from the larger pistons pumping action. Add a larger bore carb, which normally most will do when going big bore & that will displace even more crankcase volume. Something as simple as using alky fuel will displace some volume, not much but some.
All of the 350~370cc cylindered engines in years past that ran TT with us, all I know of had the tins removed & just about everyone of them were front runners winning races.
The tins removed, is a good thing for a strong bottom end big bore engine, the extra volume helps.
Neil

poli250 · « **Reply #4 on:** January 06, 2014, 04:05:35 PM »

lol get a new builder. on the big motors they all run welded tins good reason. pumashines point they have not done it before.

kb250r · « **Reply #5 on:** January 06, 2014, 07:21:28 PM »

No tins here..I don't have anything to compare it to to prove hp or performance loss...Could I have lost alittle on performance maybe,maybe not...but to me that is one less thing I have to worry about,because we all have seen the damage front tins flying off both welded and not...I pulled my tins off for personal preference makes me feel a little better...lol...

Pumashine · « **Reply #6 on:** January 06, 2014, 07:34:09 PM »

Quote from: kb250r;21625

No tins here....I pulled my tins off for personal preference makes me feel a little better...lol...

With more guys doing this we will find out if you really need them or not. I think a slight loss of HP is OK when you consider the longevity of your motor.

Mr250sx · « **Reply #7 on:** January 06, 2014, 08:44:11 PM »

Thanks guys. A little more info on the motor pertaining to what neil responded, it is a 370. 4
mil stroke with 78.50 bore and I do run a decent size carb, lectron 48hv on alky.

udontknowme · « **Reply #8 on:** January 06, 2014, 10:05:07 PM »

if you proposed this same subject to the hunderds of other 2t forums on the web i think 99% of the people say a reduction of volume would eqaul more power regardless of engine type or state of tune. but ive yet to see even 1 person prove this to be true atleast not in terms of total power. perhaps in the old days when port geometries were shit and pipes were crap then maybe a small crankcase works better but im not so sure that holds true with todays modern stuff. maybe just maybe if the engine was modern and mostly used at low rpm then its possible a small volume could be beneficial but i dont know. the case stuffing topic pops up quit alot on many forums and the replies seem to be mostly just urban legend passed down from what they heard on other forums with no evidence to support their statments.

ive increased case volume on engines but many other things were also changed at the same time so its impossible for me to say what affect the volume change had. ive got another engine in the works that will have a pretty good size volume increase also but determining exactly what affect it has will require everything to remain identical other than the increase of volume and that will take alot of time and money because im not anywhere near a dyno, not to mention assembling and disassembling the engine several times and im not going to post results based on speculation from my butt dyno.

then again im not so sure a volume test would have much relevance on this particular engine in stock form anyways since the final engine product will have different porting, pipe, head etc. but it would atleast prove whether or not a small or large volume was better for this particular engine in a stock state of tune, but that info may be useless to you guys since my engine is from a different manufacturer than what most of you guys are using.

if all aspects of the engine are geared toward maximum power, i like to think a larger volume is the way to go but its just a guess until i can do the test and prove it one way or the other for myself. chances are it will never happen but it would be nice to get enough free time to find at what point the volume becomes too large

JasonB · « **Reply #9 on:** January 08, 2014, 01:54:26 PM »

interesting topic, i swear i saw this same basic discussion over on the cr500 boards and they swore against removing the tins. My CR500 crank is off being rebuilt right now

sangheraent · « **Reply #10 on:** January 08, 2014, 03:39:41 PM »

my tins are removed, Im not sure if the engine makes more or less power but I think it reduces the hit and the lower weight on the crank helps it rev up a little faster does that mean more power I don't think so. My bike is a +4mm 310 and it revs up pretty quick it has the torque a 310 should have and acts a little like a 265.

udontknowme · « **Reply #11 on:** January 08, 2014, 10:53:14 PM »

Quote from: JasonB;21781

interesting topic, i swear i saw this same basic discussion over on the cr500 boards and they swore against removing the tins. My CR500 crank is off being rebuilt right now

youll see it discussed on most every forum at one time or another. problem is alot of the people participating in the conversation are incompetant in the subject of case volumes ( and engines in general) and just repeat urban legend they heard from some other forum. if increasing the volume of one specific engine gives less power, i dont think you can make a blanket statement and say all engines will have the same results. which is basically what that guy did on that cr500 forum your refering to. so i would caution you from believing everything you read. the best thing is test it yourself then you can know the real answer

05450r · « **Reply #12 on:** January 09, 2014, 11:50:18 AM »

Not an answer but some reading on the subject. Im by no means an expert but I was wondering if/how it would change the flow, or turbulance with them removed. I have never seen a crank without out the tins so Im just trying to learn!
http://www.macdizzy.com/cranks.htm

C-Leigh Racing · « **Reply #13 on:** January 09, 2014, 12:04:11 PM »

Quote from: udontknowme;21819

youll see it discussed on most every forum at one time or another. problem is alot of the people participating in the conversation are incompetant in the subject of case volumes ( and engines in general) and just repeat urban legend they heard from some other forum. if increasing the volume of one specific engine gives less power, i dont think you can make a blanket statement and say all engines will have the same results. which is basically what that guy did on that cr500 forum your refering to. so i would caution you from believing everything you read. the best thing is test it yourself then you can know the real answer

So true.
If a larger void is created, then somethings got to fill that void if the crankcase flow is to remain the same, but, will the design of engine your building, will that difference in the void affect its performance, maybe, maybe not.
In drag, everythings got to move fast, because most think the engines got to turn 500 billion rpms to make hp, so that voids got to be tight so the flow will move quick.
Sometimes a lot of engine is needed cause a rider cant ride, so got to do something to out run the others & they think that void needs to be tight.
The craziest thing I ever seen, was a kid on a short swingarm quad & a warm built engine, smack down on some high dollar drag builds, why, cause that kid could flat out ride with that short swingarm.
Neil

Rupp250 · « **Reply #14 on:** January 09, 2014, 01:59:06 PM »

Interesting topic that comes up on all forums.

This is why I paid a reputable builder to do my engine. Because I just don't know enough about this stuff.