Rod Length?

[dquarton]

Can anyone tell me the length of a short rod crank eye to eye? Trying to figure out what this crank is in the motor I just took apart. The rod says "KS 7" and then the number 6, is this an OEM crank? Also, it is welded on the ends, does that mean that is might be trued and welded? It came out of a motor that was set up for drag racing. Here is a pic:

http://i40.tinypic.com/mads8x.jpg

[rk88r]

The long rod is 130.3. The short rod is approximately 125.

[dquarton]

Thanks, this is a short rod. Any idea if it is OEM?

[superman]

It looks to be OEM like the ones out of the 85' ATC bottom ends...

[C-LEIGH RACING]

When you look at how the crank has been welded, it looks like it has been a plug inserted & then the plug bored to the standard stroke location for the big end pin, but then again, you cant tell how thick the insert is at the bottom because of the welding.
If it was a stroker crank, the part of the insert you can see at the top, would be real thin to move the big end pin to the outside of the crank web.

You cant see the bottom side of the insert, because of the welding & the insert could be thin on that bottom side, which would make it a D stroked crank.
Some of the Saber 500 cylinder engines, had a 70mm D stroked crank.
Neil

[dquarton]

OK, well, it came out of a motor with an ESR 350 cylinder and no spacer place, so could we assume it is a standard short rod crank? Or does the welding indicate that it is stroked?

[C-LEIGH RACING]

What I'm saying, when you look at the crank, that plug that has been inserted & then welded in place, if it was a stroker crank the part of the insert you can see, would be real thin, but its not.

By the cylinder NOT using a spacer plate, theres several things could be going on there.
#1
Could just be a short rod STD stroke crank & by that, no spacer plate would be needed in the engine build.
#2
It could be a D stroked crank & then by that, no spacer plate needed.
#3
Could be a spacer has been welded to the base of the cylinder, all welds machined off & you cant tell the spacer has been added to the cylinder casting.

If that crank, has had that plug inserted into the crank & then the pin hole bored back in the same spot as where a STD stroke crank pin would be located, then why would someone do that, unless that crank was a stroker at one time & now converted back into a STD stroke crank.

My bet, is that it is a D stroked crank somebody had from one of the Saber engine builds not being used & used it along with a 350 cylinder to get another engine running.
Neil

[dquarton]

Thank you so much for the information. This is why I try to avoid buying motors from the guy that 'bought if from the guy' that built it. Which is the case here. I would like to list this crank for sale, but would not really be able to say for sure what the heck it is!

[C-LEIGH RACING]

Put up some more pics of that crank if you would, like with the rod straight up & of both sides.
Neil

[370powervalve]

I seen this crank listed on eBay as a short rod 5 mil crank, is that for sure what it is?? Doesn't sound to me that we really know for sure. Neil can you chime in here please, I'm interested in it if we can get it figured out. Thanks.

[Langbolt]

KS 7 is a '87 CR250 Connecting rod

KA 4 is the '86 TRX/ATC rod

http://www.eddie-sanders-racing.com/product_p/short%20rod%20125.3.htm

:devil:

[RYANHENRY]

i also have this in my watched list on ebay and interested in it sooo is it a true 5 mill stroker ?

[C-LEIGH RACING]

Originally posted by 370powervalve
I seen this crank listed on eBay as a short rod 5 mil crank, is that for sure what it is?? Doesn't sound to me that we really know for sure. Neil can you chime in here please, I'm interested in it if we can get it figured out. Thanks.


Ok, now think about this.

In the first post, that pic of the rod, has KS 7 on the side & listed in another reply as being a CR250R rod, so as I know of, none of the CR250s had a long rod version of a crankshaft, so for sure would make it a short rod.

Now if it was an 87 TRX engine rod, then it would be a long rod. The 87/88/89 model TRX engine, all had the long rod.
Honda changed that for a good reason, to remove to some degree an amount of side load off of the piston, by sitting the rod at a different angle & then adding to that, relocating the wrist pin hole in the piston to remove even more side load.

Ok now heres the serious think about part.
When you do the machining to a oem Honda TRX crankshaft, if your the one knows how to do all the machining needs be done, then you understand what the job of that crank will be once the service is completed.
Taking a stock oem TRX crank, boring the big end pin hole out larger than the 24mm hole that Honda machined in, your removing a great amount of support from the outside edge of the crank web. So in turn, you have weakened the structure of that crank by making the pin hole larger & afterwards will cause flex in an alrealy to thin of an area in the web to begin with.

I guess this is kind of hard to understand, but if you ever had a chance to see what those cranks look, like with the tins taken off, you could see what I'm talking about first hand.

Another logic, once you understand the work that stroker crank has to do afterwards, then you know full well that turning a TRX crank into a stroker & then using the short rod connecting rod, not the way to go about building a stroker crank for a good many reasons.

I could stand corrected on this & wont bother me a bit if someone jumps in & does correct it, but all I know is what my hands have touched over the years & by my understanding, that not the way to build a stroker.

That crank for sale, in the first post, has to much of a mistery about it & unless I had a full detail about it from the seller, would shy away from it.
Now if the price was right, I might buy it to & pull it apart to see what was going on.
Neil

[Langbolt]

Neil has some excellent points! As per usual...thanks Neil

Also,

With it being a SHORT Rod - 125.3mm eye to eye you would then have to use the '86 style piston....If you try to use the '87-9 piston, (pin height is 5mm higher) when the crank is turned to B.D.C. the bottom of the piston Skirt will hit the Crank cheeks - If it is a 4 or 5mm Stroker.

Have you had a piston on this crank ? What style ?

If it's a De-stroker (less than 72mm Stroke) then it will clear, as the piston won't come down as much....

Sounds like a FRANKENSTEIN Crank.....Did you measure the Stroke of it yet ?

:devil:

[C-LEIGH RACING]

If that crank in the pic is D stroked, would an old 85/86 piston skirt even clear the crank tins ??.

Langbolt,
go back to the pic & look at the plug insert in that pin hole, it is way to thick in the outer edge to be a + stroker, not unless the plug is larger than the normal 26mm used & it dont look to be by the machining.
Neil

[dquarton]

I might be better off ending the auction. I am not 100% on it and had someone do the calculations for me. Dont want to sell it to somone under the wrong application. What do you think?

[RYANHENRY]

humm ya i think ill pass on that one thanks guys

[C-LEIGH RACING]

I kinda missed that you were selling it, but anyways, I guess your right.

Lot of times, it can be a lot of confusion buying & selling 250R parts, because the ol R has been around for so long & so many different things done to them to get more hp & there are some odd parts on the market.

I wish there was a way you could put in in a bottom end, put a piston on the rod, mount the cylinder & then measure the stroke of it, that would really help a lot.
Just because it is a CR rod, realy dont mater, because the CR & old 85/86 TRX used the same lenght connecting rod.
I believe the CR rod, might have been just a tad heavier made than a TRX rod.
Neil

[Langbolt]

Originally posted by C-LEIGH RACING
Langbolt,
go back to the pic & look at the plug insert in that pin hole, it is way to thick in the outer edge to be a + stroker, not unless the plug is larger than the normal 26mm used & it dont look to be by the machining.
Neil

Yeah....I see that...and the weld to the left.....almost looks like the insert isn't completely cylindrical.....more like a 1/8 MOON shape. Definitely a D-stroked crank as the pin has been relocated closed to the crank centers.

Hense the FRANKENSTEIN crank...quote....LOL

It's amazing all the weird things for the 250R that are now coming out of the woodwork....that's why the newbies are so lucky to have a site like this to talk about parts with the guru's before they make a mistake in buying something that isn't going to work for them.

:devil:

[mx91a]

Using a caliper measure from the OD of the crank main bearing surface to the center of the lower rod pin, multiply by 2 then add the diameter of the crank main bearing surface to that and there is your stroke. (assuming there is no tricky offset ground pin or something like that)

To be more accurate in finding the center of the rod pin measure the OD of the pin, then measure from the OD of the main bearing surface to the outer edge of the rod pin along an imaginary line going through the center of the crank and rod pin and subtract half the rod pin diamter from that dimension.

[dquarton]

So we can call this the "mystery crank"! Maybe I will re-list it as a mystery crank, and that will intrigue people enough to bid on it. I am also considering using it as a small boat anchor.