Offset grind a crank

[Anonymous-0]

If you offset grind a crank 1 inch, does that add one inch of stroke or .5 inches of stroke.

 

[Anonymous-0]

If you could offset grind a crank 1 inch it would add an inch in each direction up and down total of 2 inches . if you offset grind a crank .5 inch the total up and down would be 1 inch .

 

[Anonymous-0]

You only increase the stroke the same as the ammount you offset it. Ofset grinding only moves the centerline of the crankpin half of the ammount you grind. Offset 1" gains .5" up and .5" down. total of 1" increase.

 

[jd b puller]

Offset grinding is in general a terrible way to go if that"s ALL you do. It doesn"t cost that much more to weld it up and do it right.

In your example, if you had a 3" journal and offset ground it to 2", yes, you would gain 1" of stroke for about the first 5 minutes. Then you would likely have a 2 piece crank.

What tractor are you playing with?

 

[Anonymous-0]

wrong,champ

 

[Anonymous-0]

I think you guys are full of it, when you offset grind you only grind on the inside throw of the crank tot pull the piston deeper into the cyl.You don't grind on top side of crank dummys

 

[Anonymous-0]

playing with a case 900 already stroked to 7 in. with a big journal. making a set of rods and figured to go with a smaller journal to add a little more stroke.

 

[Lamont]

I think this is what grinder is trying to explain below. ??????

 

[Anonymous-0]

If you add an inch in each direction you still only added 1 inch to your stroke. Stroke equals the total distance the piston travels either up or down not up and down.

 

[C.R.B.]

offset grinding only adds to the down stroke not the upstroke like on a true stroker crank. Your only removing material from 1 side of the journal to make a smaller journal. think about it that is y its called (OFFSET GRINDING)

 

[Lamont]

It is IMPOSSIBLE to add to the downstroke without adding to the upstroke. The piston always moves the same amount in both directions.

 

[Anonymous-0]

The piston moves the same difference up or down always.

 

[Lamont]

If pulls the piston deeper into the cylinder at the bottom of the stroke, that will also push it higher into the top of the cylinder at the top of the stroke. Think about it. The distance from the centerline of the crank to the top of the piston is the same whether it is at the top of the stroke or at the bottom.

 

[Jon 400]

It will only push the piston further up the cylinder if you add metal to the outside radius of the rod journal of the crank

 

[WTW]

Grinding .250 from the inside of any given rod journal will gain you .250 stroke, not .500. The reason being is the stoke is determined by where the centerline of rod journal is in relationship to the centerline of crankshaft main journal. When grinding the inside circle of a rod journal .250 the "centerline" of rod journal only changed .125. Moving the centerline .125 further away from main journal center will cause piston to move .125 further forward and .125 further rearward gaining a total of .250 "stroke". So for example if you offset grind a crank with a 5.5 stroke with a 2.75 rod journal diameter down to a 2.50 rod journal diameter, you will gain .250 stroke. Piston will move .125 further forward and .125 further rearward. To answer your question, if you had enough journal to offset grind your crank 1 inch you would gain 1 inch of stroke because you only moved the centerline of journal .500. The way to look at it is to always refer to how much you changed/moved the center line of rod journal in relationship of centerline of main journal. Take this value and multiply it by two and you will have your total stoke value. DW

 

[D Slater]

If you remove all the material from inside throw and use the same piston and rod with thicker bearing to make up for throw that is now undersize when that piston gets to top with the thicker bearing between rod and part of crank that no material was removed from that piston will be higher in cylinder. Even if you used a rod with smaller big end and kept the same center to center distance from piston pin to big end and use the same thickness bearing as before the rod journal center line has ben moved and piston will still go higher and lower. If the rods used same center to center distance the one with smaller big end would be a longer distance from piston pin to rod bearing back surface and put piston back up to same height as big end rod with thick bearing. I'm with the ones that say more up and more down.

 

[life of riley]

Actually champ is right. It has nothing to do with adding material to it. If you cut one side and pull it .25" deeper, it will ALSO push it .25" higher. Think about it like this. Turn the journal to where it would have the piston at the bottom of the bore. Cut .25" off the side of the journal closest to the cylinder and it lets the piston come .25" closer to the bottom. Then turn the crank to where it's at the top of its stroke (the journal now pointing towards the head). That side you cut off is now the one closest to the oil pan. That means its letting it sit higher in the bore too. So to make a long story short, cut 1/4" off one side of the journal and you gain 1/2" of stroke. Difficult to explain without actually showing it in person.

 

[life of riley]

Right Jak, but if you add one inch in each direction, it means it's going an inch deeper and an inch higher. That's a total of 2" more it's moving, making it a 2" longer stroke. Keith Merfeld explained it to me like this. He stroked a G crank to 8.75" for me (it was 7" stock). To gain the extra 1.75" stroke I wanted, he said he would add .875" to the back side of the crank so it pulled it .875" lower and pushed it .875" higher. The total of that is 1.75", which he explained made my total stroke 8.75".

 

[life of riley]

Read my post below in response to Jak for maybe a little better explanation. I wrote it how Keith Merfeld explained it to me once.

 

[Anonymous-0]

WTW did a very good job of explaining this. I have been grinding cranks for many years and have found that a lot of people just do not understand how offset grinding works.

 

[Lamont]

How can changing the diameter of the main bearing journal by .875" add 1.75" to the stroke? That would move the radius of the journal only .4375". That would be how much the distance changed between the center of the main journal and the center of the rod journal. In other words, the throw would only be .4375" longer. Do the math.

 

[life of riley]

As per him, it's because you add the entire .875 to one side of the journal, the grind the other side down and true it all up. If you add it to one side, then it pulls it .875 lower and pushes it .875 higher. Getting the 1.75 total.

 

[jd b puller]

Riley, if you have to quote someone else, you don't really understand what's happening. Everyone is allowed to have an opinion, unfortunately this is sort of a math/fact based discussion. It's apparent that you don't really understand this. Draw it out on a piece of paper. If I could figure out how to post a pic, I'd show you a CAD drawing so it would make more sense to you. Sorry if I sound like a b-hole, but the nonsense is gettin' to me.

In essence, all you care about is the CENTERLINE of the journals. If you take a 3" journal and leave the outside edge where it is and Offset grind it to 2", you move the CENTERLINE 1/2". The distance from the center of the crankshaft to the CENTERLINE of the rod journal is 1/2 the stroke. So, say it is 3" from the center of the crank to the centerline of the 3" journal - you have a stroke of 6". Now, (draw a picture if it helps), Draw the 2" circle with the outside edge touching the original journal. How far is the center of the new journal to the center of the crank? It's 3.5". So what's the stroke? 7.00" So, you took away 1" of material off the inside of the journal, moved the centerline 1/2" and added 1" to the overall stroke.

 

[Lamont]

There is a hand-drawn picture above. It's sort of crude but explains exactly what you're saying. Sorry I can't draw any better.

 

[Lamont]

So he's adding to the outside AND grinding the same amount off of the inside? That makes sense. In essence, the actual diameter of the main journal is not changed at all. That would move the center of the journal .5 X the total amount of grind on inside AND .5 X the total amount added to the outside. Adding .875" to the outside moves the center .4375". Grinding .875" off the inside moves the center an additional .4375". Center of main journal to center of rod journal gained .875". Total stroke change 1.75". Clear as a bell. If that's how it's done-that makes perfect sense.

 

[Anonymous-0]

To restate, if a piston travels up 5" inches then it must travel downd 5 inches for a total of a 5" stroke. I think nearly everone agrees as to how a lengthened stroke is acheived. I also think statements have been misundrestood or said wrong which has caused all the confusion as to who thinks what.

 

[life of riley]

Right, that was my understanding that whatever is added to one side, the same amount was ground off the other side. Otherwise I see what you're saying where it would be only half.

 

[Anonymous-0]

Real easy to explain fellas. Measure between centerlines and multiply by two.

Draw your smaller journal at the bottom of the larger journal and measure between centerpoints. Multiply by two....STROKE!

 

[Lamont]

Sure does help when we're on the same page!!! I've always thought that the grinding would sure weaken that main journal, but it makes sense just to add it back to the outside to keep the strength.

 

[bigdog88]

looks like a lot of you don't really have a clue what you are talking about, offset grinding a crank like a 99 oliver with i think a 2 5/8 journel and using c farmall rods with a 1 3/4 journal will give you just under 1 inch of stroke which is all picked up on the down stroke, leaving the outside of the crank journal alone will not make the piston travel higher only lower in the block.

 

[AW Puller]

You are right, several people in this thread dont have a clue, and you are obviously among them.

A couple people have PROPERLY explained it already, so I wont try to again.

From some of the stuff I have read in this thread, there are several people that have no business with a wrench in their hand!!

 

[Lamont]

Piston travel above the center of the main will ALWAYS be equal to piston travel below the center of the main. Think about it.

 

[Lamont]

Scratch the words "center of the main" and insert "center of the stoke."

 

[Anonymous-0]

offset a crank 1 will give you 2

 

[AW Puller]

You said: "offset a crank 1 will give you 2"
NOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!

Why is this so difficult?? It has been explained countless times in this thread already and people cant seem to figure it out.

If you offset grind it 1", the centerline of the crankpin is moved .500" out from its original position. So that is .500" more down and .500" more up, for 1" total increase.

If the crank is welded up 1", and the crankpin size stays the same, then the centerline is moved out 1.000"....1.000" more up and 1.000" more down, for a total of 2" increase.

 

[Anonymous-0]

OK i get your point but if i tell my crank guy add a inch of STROKE i will expect an offset of 1/2. If i tell him OFFSET 1 i will expect 2. I do understand what your saying but the man asked stroke not offset

 

[Earl-IL]

To clear this up, go look at the heads of your crankgrinder & you can better understand the offset of the centerline of the rod journal to the centerline of the main.

 

[bigdog88]

look, if you offset grind a crank 1 inch you will get 1 inch of stroke. you grind the 1 inch off of the inside of the journal thus when the piston is at bottom dead center it is 1 inch deeper in the hole and when it is at top dead center it is at the original heigth. all of you go look at what machinest posted he hit the nail on the head.

 

[D Slater]

Don't think it will do any good, but think about what you are saying. If you remove the material from rod journal on the side toward main journal center line and leave the side away from main journal the same. When the rod throw is all the way up or all the way down the same uncut part of crank will be fartherest from main center line. Or when crank throw is up uncut part is to top and when throw is at bottom uncut part is to bottom. So if throw or rod and piston goes down farther from center of main center line it has to go farther up also, unless center to center distance of connecting rod is changed. Only way same center to center rod would go down and not up is if you put rod and same bearing as before cut back in and gravity would make it fall farther down and it would go up no farther than before but with all the space between crank and bearing its up and down would be short lived. In your other post are you comparing rods with a different center to center distance?

 

[AW Puller]

"Machinest" didnt hit the nail on the head, he missed completely and smashed the he!! out of his finger next to the nail instead. He is just as wrong as you are.......as in VERY wrong. He!!, I dont think he is really a machinist anyway, seeing as he cant even spell it right!!!!!!

You need to put the wrench down and step away from the tractor. You obviously arent bright enough to work on one.

 

[Keddano]

So if I Offset Grind my crank 1" and I have 6 cylinders I added 6" of stroke... right!
JUST KIDDING L.O.L.

 

[Earl-IL]

The stroke is the length or distance a piston travels up & down in a cylinder.