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Tractor Pulling Discussion Forum

stroking

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tractor fan

10-10-2007 14:57:32

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Can someone tell me if i'm correct. When you offset grind a crank, you cut down one side of the journal, allowing the use of a smaller journal rod and also increasing the throw of the crank. 1/2 inch of material off of a journal yeilds 1 inch of total stroke? , but dosen't really make the crank swing any farther out.

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big stroker

10-14-2007 11:33:28

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

B-maniac what you don't understand is offset grinding, you only grind off of one side that is why it is called offset. and I do know cause i took a oliver 99 crank and used c farmall rods whitch have a smaller journal bore and offset ground the crank all off of the inside and gained somewhere around .900 of stroke, it didn't matter where the center line was cause you don't grind anything off of the outside of the crank to need to know center line, so if you have a crank with 2.500 rod journals and you change to rods that have 1.750 and you offset grind everything off of the inside of the crank journal you will pick up .750 of stroke all at the bottom and none at the top assuming that the rods are the same length one more good example is with oliver stuff, using a stock 77 rod and a super 77 crank whitch is .250 bigger and offset grinding the inside of the journal you will pick up .250 of stroke all at the bottom.

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jd b puller

10-14-2007 15:39:27

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Re: stroking in reply to big stroker, 10-14-2007 11:33:28

Instead of confusing yourself trying to explain it (Which you've bumbled thru to the point where I think you believe yourself). Stroke is defined as>>>

- 2 times the distance from the CENTER of the rod journal to the CENTER of the MAINS...

- Using your "logic", you should just make the journals 6" in diameter, think of all that "stroke" you'd be adding.

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big stroker

10-14-2007 17:10:05

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Re: stroking in reply to jd b puller, 10-14-2007 15:39:27

no wonder you JD's can't keep trying to stroke a tractor like that

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big stroker

10-13-2007 14:17:10

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

offset grinding a 1/2 like told to you guys before will only give you a 1/2 inch of stroke by grinding the inside of the crank, the piston height will not change at top dead center because you are not changing the side of the crank that controls the rise of the piston, only the draw down in the cylinder, so where you gain the stroke is at bottom dead center, and it is only a 1/2 inch that you gain, not a 1/4 here and a 1/4 there only 1/2 inch at the bottom, hope all of you what is the center line and 1/4, 1/4, people don't build engines for a living.

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Drew

10-16-2007 18:05:00

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Re: stroking in reply to big stroker, 10-13-2007 14:17:10

Maybe a picture will help explain all this.

This example is a 6.750" stroke crankshaft, with a 1/2" offset grind to increase the stroke to 7.250". As you can see, the centerline of the journal moves 1/4" up and 1/4" down from the original location.

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B-maniac

10-19-2007 18:25:44

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Re: stroking in reply to Drew, 10-16-2007 18:05:00

Now if you all can just picture a rod with an 8" center to center installed on the larger journal..where the wrist pin center would be ,,and then an identicle rod of 8" center to center mounted on the small journal , it's pretty plain to see that the wrist pin centerline and thus the piston WILL be 1/4" farther out towards the head from the main centerline. You absolutely have to think outside of common sense and consider centerlines in this case. It is what it is!

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jd b puller

10-16-2007 18:29:54

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Re: stroking in reply to Drew, 10-16-2007 18:05:00

Oh, there you go bringing math and CAD drawings into a battle of speculation and opinions...

Course, you know that will only work for a JD A :-)

What were you thinking Drew?

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B-maniac

10-13-2007 19:10:34

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Re: stroking in reply to big stroker, 10-13-2007 14:17:10

Well Drew and Big Stroker , you are both correct but your reasons and explainations are wrong and incomplete. Big is looking at it as the original rod sitting atop the reground rod journal as not sitting any higher in the bore than it did before. He is correct.It would only gain stroke at the bottom of the stroke. BUT! We are not going to use the original rod! This is what neither one of you have explained , so I will. If the stock rod center to center length is say 8" and you purchase the smaller journal rod to fit the re-ground crank with the same center to center length of 8" then this is where the "new" center line of the "new" 1/2" offset ground journal comes into play. When you grind 1/2" off the bottom side of the journal , it automatically raises the centerline by 50% of that or 1/4". Now when you install that new 8" rod , the piston end center line is 1/4" farther to the top of the bore than it was before. So you see it's the way we measure rods that has as much to do with this as offset grinding does. The new centerline of the journal is 1/4" higher up or farther out from the main journal than it was before so the new rod with a center to center length of 8" , same as the old one, will in turn be 1/4" farther out or higher up on TDC. It comes down to how we measure rods. If you could leave the original rod on there and shim the rod cap to compensate for the 1/2" grind off then Big was right in what he said. But , we can't do that! As long as rods are measured center to center and we "move" the centerline of the crank pin then we HAVE to move the center of the piston pin also. This would be equivalent to staying with the large journal dia. and moving it out from the crank centerline 1/4". The crank pin centerlines would be identicle and the piston would go up 1/4 and down 1/4 for a 1/2" stroke increase. In automotive engines you would have to use a piston with a higher pin location so it wouldn't hit the head. This means you get all your gain on the down stroke. A tractor might have such a large piston to deck height for low compression that you could use the original piston and gain the extra bennefit of increased compression also. The whole thing ballances on whether you can get the custom rod you need at a reasonable price.

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Gump as in Forrest

10-14-2007 14:03:52

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Re: stroking in reply to B-maniac, 10-13-2007 19:10:34

You are incorrect, and that"s all I have to say about that.

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B-maniac

10-15-2007 18:39:28

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Re: stroking in reply to Gump as in Forrest, 10-14-2007 14:03:52

Either draw it out on paper or do it on auto-cad.Mike , JD-B , Skip , Drew and myself have obviously already done so. It's pretty simple. When you move the rod journal centerline away from the main centerline and then add a small journal rod with the same center to center dimension as the original , and the same piston as original , then the overall dimension from crank center to piston pin center is longer whether it is on upstroke or downstroke. The only way it would be all on the downstroke is if you were to shorten the piston the amount of the increase so as to not hit anything above. By doing that you gain double at the bottom. At the bottom ,then, you get the 1/4 stroke increase and also the head of the piston is now also 1/4 lower giving you the whole 1/2 at the bottom. Big Stroker , believe me , I was with you 100% at first but thinking and drawing and realizing we are not using the same rod proves that this new center and new 8" rod WILL be 1/4 higher even on the upstroke.Sorry but I have to stand by it.

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Gump as in Forrest

10-16-2007 08:05:25

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Re: stroking in reply to B-maniac, 10-15-2007 18:39:28

I can and have ,I do understand the man wanted a simple yes or no answer. Then you guy's assume Rods etc. Yes his question was vague but none of you asked compression height,ratio etc. you all want to argue. Most of the post's were somewhat correct. The man just wanted to know what the stroke was with a 1/2 inch offset grind, and That's all I have to say about that!!!!!

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Drew

10-13-2007 16:24:11

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Re: stroking in reply to big stroker, 10-13-2007 14:17:10

Are we going to have to go over this all over again???? People that replied BEFORE you are correct. A 1/2" offset grind will add 1/2" inch stroke, 1/4 inch higher and 1/4 inch lower. I really dont know how to make it any more clear for you. Would pictures help?

Hope you dont lose a lot of sleep over it, but I do work on pulling engines for a living. I think you are the one that we should be worried about working on engines.

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hey drew

10-14-2007 07:45:01

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Re: stroking in reply to Drew, 10-13-2007 16:24:11

you can't build squat! Just a big talker! OOOHHHHH SCARY!!!!! PUTT PUTT BANG BANG

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tractor fan

10-11-2007 21:53:39

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

So if the rod journal was 2 3/4 inches, how much could it safely be stroked?

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tractor fan

10-10-2007 22:32:29

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

Ok, thanks. But am i correct in saying that by offset grinding there is no new clearance issue because the outermost portion of the crank still swings out the same distance?

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Jim in OH

10-11-2007 14:12:02

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Re: stroking in reply to tractor fan, 10-10-2007 22:32:29

tractor fan said: (quoted from post at 22:32:29 10/10/07) Ok, thanks. But am i correct in saying that by offset grinding there is no new clearance issue because the outermost portion of the crank still swings out the same distance?

There is no new clearance issue with the crankshaft but there may still be clearance issues with the rods and rod caps... for example the cam or cam gear (to the distributor) may get in the way, or the oil pickup, or even the block, etc... also, don't forget that you will need shorter rods or a shorter compression height on the piston to avoid piston clearance issues..

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Mike n Mo

10-10-2007 18:05:25

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

Offset grinding by removing the 1/2" of material on the inside of the crank throw per your example will increase the total stroke by 1/2". That would move the centerline of the crank throw by 1/4", thus moving the piston further in each direction by 1/4". An extra 1/4" each direction yields a 1/2" total increase. Hope this makes it clear. Mike

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skip33652

10-10-2007 18:01:30

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

1/2 inch material off one side of the crank will yield 1/2 "total stroke increase.grinding 1/2" off of one side will move the center 1/4" swinging both ways ( up and down) will make 1/2" increase.Paul

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jd b puller

10-10-2007 15:02:28

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Re: stroking in reply to tractor fan, 10-10-2007 14:57:32

Oh boy, here we go again.. Just went thru this a couple months ago... make this simple, DON'T read the archives...Doesn't matter what the inside or outside of the journal is, the only thing that matters is the centerline.

1. What is your current stroke?
2. What is your current Rod journal diameter?
3. What are you going to make your new rod journal diameter?

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Robert Warner

10-14-2007 11:04:52

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Re: stroking in reply to jd b puller, 10-10-2007 15:02:28

Why are we even talking about offset grinding? Stroke the thing and be done with it!!!!! !!!!

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jd b puller

10-14-2007 15:34:45

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Re: stroking in reply to Robert Warner, 10-14-2007 11:04:52

I guess people think they can save money by half A$$ing the job... I"m with you, get in or get out... You"ve got the crank out, you"ve got to take it somewhere to get it ground. For half again as much, you can get it done right. Can"t figure out why people can"t figure out this offset grind thing either. Big Stroker, I thought he knew what he was doing, until he opened his keyboard last time.

Centerline, centerline, centerline...

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tractor fan

10-14-2007 17:51:35

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Re: stroking in reply to jd b puller, 10-14-2007 15:34:45

Some people just can't afford to pour a bunch of money into a big cube engine that may blow up next time you open it up. There's something to be said about reliability and simplicity. The motor that i'd like to stroke is an rd 450 ih motor. You probably don't know much about these motors, but there isn't alot of room inside them to "stroke big". I do know this though, this motor with a little, half a$$ offset grind would wipe your "big stroke" b or what ever the heck john deere you pull right off the track. I'd like to thank all of you for the input, it was very helpful.

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jd b puller

10-14-2007 18:49:18

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Re: stroking in reply to tractor fan, 10-14-2007 17:51:35

Actually, I'm kinda flatterred - You just compared an RD450 IH to a JD B. Next we'll have the the 1000 cube Minnies challenging the 456 cube B... Do you play quarterback on your kids Jr. High Football team too?

No, don't know much bout them motors.

Like the other guy said, if you're going to all the trouble of pulling the crank, do it right. I think you kinda contradicted yourself there too.

"Some people just can't afford to pour a bunch of money into a big cube engine that may blow up next time you open it up" -- Last I checked it took money to build a big cube engine no matter how you do it. And it won't be a "big cube engine" without a decent crank in it.

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Robert Warner

10-14-2007 18:32:56

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Re: stroking in reply to tractor fan, 10-14-2007 17:51:35

I cant believe you just compared an IH 450 to a John Deere B. The only thing we're saying is you get more bang for the buck if you stroke it instead of offset grinding it. Save your money and stroke it later down the road. I was thinking of offset grinding my crank but then I realized I didnt want to tear the engine down again and spend that money all over again. We was just trying to help ya!

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tractor fan

10-14-2007 20:58:56

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Re: stroking in reply to Robert Warner, 10-14-2007 18:32:56

You guys, including jd b did a fine job of explaining the subject. It just kind of aggrevates me when people just tell you to buy this or pay someone to do it for you. The whole reason I'm messing with the rd450 is because for a few thousand dollars you can have a big(by ih standards) engine that will be pretty reliable. I can't afford to build a big engine more than once. I'm not intrested in punching it out as far as it will possibly go. I just thought that my offset grinding I could get a half to one inch of stroke, wouldn't have any major cleareance issues, and be able to use cheaper, more avaliable rods and such. I'd like to thank you guys for helping me out and did not mean to disrespect anyone. I just got caught up in the posts. Once again, sorry and thanks

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jd b puller

10-15-2007 15:11:22

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Re: stroking in reply to tractor fan, 10-14-2007 20:58:56

Just keep in mind that even with offset grind, you are losing considerable strength in your crankshaft. Relative Strength being a function of the SQUARE of the Diamter. No clue what the journal dia is, but if you're taking off 1/2" it must be somewhere around 2.5". Going to 2" would be losing roughly 36% of the original area.

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mlpankey

10-10-2007 22:38:51

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Re: stroking in reply to jd b puller, 10-10-2007 15:02:28

theres alot of them out there granted i dont run that rod anymore but i do use the block still that had them in it . it lasted five years before the no 4 rod journal broke into . the rod was still straight and hadnt stretched its just the crank journal is really weak at those journal sizes.

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