Replacing a crank shaft questions

[like_A_pike]

Any forged rotating assembly that will work gentlemen. Shop says they can "stroke it" if I want.

 

[cudamark]

I think we're still trying to understand what is wrong with your crank, and what you plan on having when you're done building the engine. Street cruiser? Drag racer? Something in between?

 

[Professor Fate]

Why do I feel like a dentist here? It's like pulling teeth to get any basic info. What exactly are you trying to build? Stock-ish shortblock? Stroker? Why does the shop deem your crank to be toast? If it's scored, a light grind to the smallest undersize takes care of that. Is it twisted? Or do they just want to take more of your money?
You asked for advice- give us some info. Pics are nice but they don't tell you journal condition or if it's been ground or to what undersize... We're just trying give you the answers you need and maybe save you some grief along the way. This isn't the Manhattan Project, no need for secrets.

 

[Wyrmrider]

what do the mains mic at?
what do the rods mic at?
how much will it take to clean them up?
if you have bad rod journals you can turn for chevy rods (which is not a bad idea anyway) find your rods and pistons first
you can find chevy crankpin rods with either mopar or chevy pin size
no good crank grinders in East TX?

 

[1966Post]

Sometimes you feel like your banging your head against a wall and hitting a stud every time. In those cases it’s best to follow the Frozen song and let it go Let it go...

 

[like_A_pike]

ok, so the wife and I are juggling our careers here at home with a 2 year old in the middle of poddy training. its a train wreck all the time around here.
then The Shop, that hadn't contacted me for 4 weeks, tell me that the crank is scored quite badly. I didn't ask for much more detail than that because it was pretty bad in early 2012. the 340 was a private sale from a guy near Ellensburg Wa. I put it together and drove it 1000 miles and it started making alot of noise and leaking oil from the rear main. Took it apart noticed that the bearing might have been put in wrong so I replaced it and the thing melted down a second time. I moved to Jacksonville Fl.and had a shop there line hone the block and It seemed ok. Ran good but always left me some metal in every oil change. It was just a mater of time I always figured. It ran good really, used about a quart every couple thousand miles and ran 13.3-13.5 quarters a couple times a year. Always trying to get under 13.... So the last 5 years in east Texas it ran 5K a year with a little test and tune mixed in. Thats what I use it for that's where Im headed. water pump broke last month and it overheated. Enough to diesel after i turned it off for a couple minutes trying to get it to stop. Had a local FABO member / racer recommend The Shop, double checked with a performance shop that actually farms their machine stuff to The Shop. So I took it there to get checked out and long blocked. they've been in business forever. I think their clients often hit a financial roadblock when something goes wrong so they assumed that I would not pursue the rebuild after calling the crank "toast". It was turned many times before I got it and now it's below speck. (im told) and frankly don't care If I can replace it. Additionally the harmonic balancer has lots of holes in it so it's prolly time to start over there too if I can. So I see on ebay there are cranks but in the back of my mind know that something is weird about my model year. And I have this 1968 manual that only tells me some **** about a Maltese Cross. So I lobbed some brief and I'll admit cryptic questions your way to attempt to avoid an impulse buy. I have it down there don't have time for incompetence but sometimes you have to sail the wind you got.... So I learned alot from yall so far. that original equipment means nothing at this point, that im definitely internally ballanced and there are cranks out there after all. I honestly don't think The Shop every looked. Anyway there's where I am. I got some advice to go new if I can and to get everything to balance maybe go with a kit. I am interested in staying with the forged crank (all my interest in the original years was because of this) but only recently decided that used is prolly not the way to go with this rebuild. I am going up a cam size, still pretty modest, still like to get into the 12s and continue to terrorize Kia soccer mom's on the state roads. So I don't think I want to go with a Stoker but I have not found a 3.31 stroke kit thats forged yet. 3.5 will do in this case if all things are equal. does that help? cuz dinners ready and it's time to go pee again.....

 

[nm9stheham]

Making sense now..... And I see the rear seal surface in pix 25 looks boogered up....

So are you going with all new bottom end parts there OP? Like new pistons and maybe rods? And what heads are to be used, and do have an idea on the new cam specs? Just askin', as it sounds like everything may be on the table. But stop us before we spend everything in your bank account LOL

 

[yellow rose]

ok, so the wife and I are juggling our careers here at home with a 2 year old in the middle of poddy training. its a train wreck all the time around here.
then The Shop, that hadn't contacted me for 4 weeks, tell me that the crank is scored quite badly. I didn't ask for much more detail than that because it was pretty bad in early 2012. the 340 was a private sale from a guy near Ellensburg Wa. I put it together and drove it 1000 miles and it started making alot of noise and leaking oil from the rear main. Took it apart noticed that the bearing might have been put in wrong so I replaced it and the thing melted down a second time. I moved to Jacksonville Fl.and had a shop there line hone the block and It seemed ok. Ran good but always left me some metal in every oil change. It was just a mater of time I always figured. It ran good really, used about a quart every couple thousand miles and ran 13.3-13.5 quarters a couple times a year. Always trying to get under 13.... So the last 5 years in east Texas it ran 5K a year with a little test and tune mixed in. Thats what I use it for that's where Im headed. water pump broke last month and it overheated. Enough to diesel after i turned it off for a couple minutes trying to get it to stop. Had a local FABO member / racer recommend The Shop, double checked with a performance shop that actually farms their machine stuff to The Shop. So I took it there to get checked out and long blocked. they've been in business forever. I think their clients often hit a financial roadblock when something goes wrong so they assumed that I would not pursue the rebuild after calling the crank "toast". It was turned many times before I got it and now it's below speck. (im told) and frankly don't care If I can replace it. Additionally the harmonic balancer has lots of holes in it so it's prolly time to start over there too if I can. So I see on ebay there are cranks but in the back of my mind know that something is weird about my model year. And I have this 1968 manual that only tells me some **** about a Maltese Cross. So I lobbed some brief and I'll admit cryptic questions your way to attempt to avoid an impulse buy. I have it down there don't have time for incompetence but sometimes you have to sail the wind you got.... So I learned alot from yall so far. that original equipment means nothing at this point, that im definitely internally ballanced and there are cranks out there after all. I honestly don't think The Shop every looked. Anyway there's where I am. I got some advice to go new if I can and to get everything to balance maybe go with a kit. I am interested in staying with the forged crank (all my interest in the original years was because of this) but only recently decided that used is prolly not the way to go with this rebuild. I am going up a cam size, still pretty modest, still like to get into the 12s and continue to terrorize Kia soccer mom's on the state roads. So I don't think I want to go with a Stoker but I have not found a 3.31 stroke kit thats forged yet. 3.5 will do in this case if all things are equal. does that help? cuz dinners ready and it's time to go pee again.....

I wouldn’t spend on cent until the shop tells you how far under the crank is. Them saying it’s too far under and scored doesn’t mean a thing. As I posted earlier, there is a whole gang of people out there who think turning a crank .030 under is a crime against nature.

it’s NOT. You have no numbers to work with. FWIW I refuse to use cast cranks. There is no reason to do it, other that to save a few bucks.

Long before I scrapped a crank the machine shop would have to provide me with numbers. Can you read a micrometer? If so, go in there and mic it yourself.

 

[like_A_pike]

Making sense now..... And I see the rear seal surface in pix 25 looks boogered up....

So are you going with all new bottom end parts there OP? Like new pistons and maybe rods? And what heads are to be used, and do have an idea on the new cam specs? Just askin', as it sounds like everything may be on the table. But stop us before we spend everything in your bank account LOL

This artifact has hand ported 587’s and formerly the Comp 232-4 I’m trading for Comp 224-4 to better match my 3500 stall converter.
I posted a SCAT rotating assembly kit and balancer add from Jegs earlier to get some opinions. I am going to reach out to the manufacturer when I can
either way.

 

[Wyrmrider]

you can also cut down a 360 crank for more piston availability and another 20 cu inches and 20 ft lbs of torque- which you can feel especially with an auto trans
if you just need a crank first do as YR says one score is not fatal especially in the center where there is an oil grove anyway
there are cranks out there
318 crank is going to like light pistons or else heavy metal to balance
Scat not Eagle if getting a kit
strokers also have more piston choices
saving a few bucks is a consideration and cast cranks are fine for a street build with an AT you are not going trans am racing
that said if you need pistons go light maybe even with a longer chevy rod makes a big difference on how the motor revs
and you are removing weight from the crank not adding
+ if you get a 318 crank and 318 weight 340 pistons you might not even have to balance
lots of way to skin a cat
you must have a great wife

 

[nm9stheham]

FWIW.. stock 340 pistons won't balance with a 318 crank; you have to add weight. But I doubt that the OP is going with old heavy 340 pistons.

That SCAT assembly is the easy way to go, if you want to upgrade and solve it with $$. Fair piston choices and they have a kit that probably has forged and cast crank options, internally balanced option, lighter SCAT rods, 340 mains, 3.58" stroke, Icon 360 flat tops in oversizes for .020, .030, and .040" overbores in a 340 block, and just under 10:1 static CR with the present heads if they have not been milled a lot.

I have not looked up the proposed cam but the dynamic CR may be a bit lower that optimum for pump fuel; that ought to be looked at before you make a move. But there is one ICON forged piston option with a dome that might make up for a biggish cam; the domes might need a bit of milling. (And only in a .020" oversize for the 340 block in the ICON catalog.) Knowing the chamber volume on your heads is necessary.

And there are 4" stroker options too. SCAT can often work with you to vary the options mix on their kits.

 

[nm9stheham]

This artifact has hand ported 587’s and formerly the Comp 232-4 I’m trading for Comp 224-4 to better match my 3500 stall converter.
I posted a SCAT rotating assembly kit and balancer add from Jegs earlier to get some opinions. I am going to reach out to the manufacturer when I can
either way.

So OP are you talking about a Comp XE274H (flat tappet hydraulic)?

What is the main goal here? Best strip times? Or daily driver?

 

[like_A_pike]

So OP are you talking about a Comp XE274H (flat tappet hydraulic)?

What is the main goal here? Best strip times? Or daily driver?

yes sir, that's the grind.
I drive it about 5,000 miles a year. It's registered and inspected. I take it as far as Little Rock in the winter.
I learned shortly after moving here that PineValley raceway was just a few miles away. Soooo I would also like to get my 60' times down a hair (1.97 with .07-.15 lights) I go 3 or so times a year when the weather allows and the temps are still below 90. Before this I used to disconnect and plug the vacuum advance and retard the distributor a schoshe to race on pump gas. I have a 3.55 for that Little Rock drive however....

 

[nm9stheham]

OK, so mixed use, mostly over-the-road driving. The cam size makes more sense now. It is not a big change, so not sure how much it is going to change the engine operation.

Very rough numbers: Dynamic CR work out to 7.75 with nominal numbers, the 3.58" stoke and flat-top pistons, and a guess that the heads are close to stock chamber size; pretty decent for keeping low RPM torque up.

Go to a 4" stroke, with flat tops, and both CR numbers jump up a about .8 points so needs some work to keep the DCR numbers from getting too high... a step bigger cam, knowing the chamber sizes within a 1 cc accuracy, thicker head gasket, all can be used, but once you push things up that far, it's really necessary to know the exact numbers on everything to work it to a reliable number.

 

[like_A_pike]

OK, so mixed use, mostly over-the-road driving. The cam size makes more sense now. It is not a big change, so not sure how much it is going to change the engine operation.

Very rough numbers: Dynamic CR work out to 7.75 with nominal numbers, the 3.58" stoke and flat-top pistons, and a guess that the heads are close to stock chamber size; pretty decent for keeping low RPM torque up.

nm9stheham, I'll take "pretty decent" anytime. what does the 7.75 refer to?
thanks again

 

[Krooser]

I have two standard journal 318 forged cranks that may clean up with a polish or, maybe, .010 under. $100.00 plus shipping. Mopar cranks are good pieces....

 

[nm9stheham]

nm9stheham, I'll take "pretty decent" anytime. what does the 7.75 refer to?
thanks again

It refers to DCR which is dynamic compression ratio. It is a computation of what you might think of as the 'effective' compression ratio of an engine with the cam's effects taken into account.

You want that number high to boost low RPM torque (below roughly 3000 RPM, where the exhaust scavenging effect dies off) but not too high, because too high means you will run into detonation problems and that is bad juju.

BTW, there are better cam profiles out there IMHO for this engine if you are open to suggestions. Not better because they are bigger in duration or lift , but better in the fact that they get the valve open more quickly and can get more charge into the cylinders. The contemplated cam change is not very much. Are you using the stock rocker package?

 

[like_A_pike]

DCR is different from an actual compression ratio though correct? DCR is like an index?

by all means, my cam research was pretty limited. I think the Purple MP 292/509 cam was on my short list.

 

[Wyrmrider]

agree with nm
you can do better than a comp old school cam
a lot of duration for the area which bleeds CR

will cut torque but run almost ok up top maybe 25 hp

 

[like_A_pike]

[

agree with nm
you can do better than a comp old school cam
a lot of duration for the area which bleeds CR

will cut torque but run almost ok up top maybe 25 hp

I appreciate that
I ran into something you wrote about the XE275HL, Can't remember where I saw it.

 

[like_A_pike]

QUOTE="nm9stheham,
Are you using the stock rocker package?[/QUOTE]

I didn't see that question. Yes nm, that was the plan this time around. I'd like to upgrade but I've got a lot of irons in the fire right now.

 

[nm9stheham]

Since your heads are ported, I'd think you would benefit from a more area-under-the-curve type of cam. I was not thinking MP, but one of the Howards cams optimized for the .904 Mopar lifter diameter. The Howards 710461-10 is such a cam and has an advertised duration of 273, but with a lift of .525". So a very similar cam in terms of low RPM torque (probably a bit better in fact), but it ought to fill the cylinders better in the mid range an up. Some thought needs to be made over the valvetrain and so that was why the question on using the stock rockers.

BTW, dynamic CR is not a index but another form of compression ratio computation, which reflects the effect on actual cylinder compression ratio and pressures, due to the point at which the intake valve closes on the compression stroke, which is typically 60-70-even 80 degrees after bottom-dead-center. With a bigger and bigger cam, that event occurs later and later and the resulting actual cylinder pressures go lower, and that effects low-mid RPM torque.

This makes less and less impact once the engine revs to mid and then high RPM's where the exhaust scavenging effect comes into the picture. But the DCR is important to evaluate if low RPM torque if important. And you also can use DCR as a check to see if your static CR and cam combination is off the mark and you are verring towards detonation-land.... not where any of us want to go.

 

[like_A_pike]

Thanks for the recommendation and DCR discussion. I found a calculator on gofastmath.com
I believe my original cam candidate required beefier springs and larger seat clearance milled in the head. All to say I think we were kinda headed in that direction with the valve train. I would like to upgrade to roller rockers, but that isn't in the cards right now. Just to clarify an earlier response.

I meet with The Shop on Monday. I’ll keep folks posted as it progresses.

 

[like_A_pike]

So with the harmonic dampener. How do I go about balancing the new one??

You don't... you get one already made. It IS possible to do one yourself with the rigth techniques and data. But even with any perchant for.... mmmmm.... creativity LOL..... I'd just buy one.

this was helpful. The multitude of shallow holes in mine were a source of much confusion.

update: the SCAT stroker kit and a Comp XE275HL K kit are on the way. I was a little concerned about the 106* lobe separation on the Howard, but the matching valve train recommendations listed in the Comp Cam Catalog tipped me the rest of the way.

 

[Nat]

i think that is a good choice for a stroker kit , i made the mistake of going big , i would probably go for the 373 cube stoke if i were to do it over ;
you'll be real happy with the power that combo will make , should be a screamer