DodgeIntrepid.Net Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
74 Posts
Discussion Starter · #1 ·
I'm trying to decide whether to rebuild a 2.7 (that spun two bearings, #3 & #4) myself, get a short block or supply the parts to a builder and have them put it together. I know at least one rod is shot from the stress as it's has burnished metal on the bearing race. It was only run for about one mile and didn't overheat.
In my research I've read that the pistons and rods are considered an assembly and matched for weight. I can get new rods but nothing is ever written by the suppliers about the weight nor is it noted on the rods themselves. I'd like to press out the piston pins so I can provide new rods to the builder but I don't know if I'd be making things ore complicated than they need to be.
Please excuse my writing. Sometimes "word" won't let me delete a letter.
Any thoughts would be appreciated.
 

·
I hit **** with sticks!
Joined
·
38,007 Posts
I've never heard of the weight matching, but as far as Mopar OE is concerned, the pistons are sold as a piston/rod assembly. Pistons/rods are available separately in the aftermarket.

I dont see weight matching being a concern; as long as the aftermarket stuff is built to OE spec it will be fine and will be the proper weight --- be careful here, cheap rods off of amazon are suspect; there are tons of counterfeit parts out there from other countries, especially on amazon etc; that are complete garbage.

The pistons and cylinders will need to be checked for wear as well, these engines are susceptible to piston slap if the pistons are even slightly worn. In my experience, if you are going this deep, I would mic all cylinders, bore as needed, replace all pistons regardless of how many rods need replaced. Any rods you think are still good, just need to check their bores and make sure they are in spec still. Usually there is not an issue with a rod unless there was a spun bearing or oil starvation.

I would suggest having the engine builder swap the rods; since they are press in; unless you are sure you have the proper tools to do it; if you've got a shop press, ok, but its a different process than pressing out a ball joint or bushing, there may be a depth or clearance spec involved---plus an oil clearance spec on the rod-wrist pin.

Be careful supplying your own parts to a builder, generally, if they agree to do it at all, it will void your warranty.
 

·
I hit **** with sticks!
Joined
·
38,007 Posts
The crankshaft will also need to be addressed if you had a spun bearing. Quick and easy way is a crankshaft kit. Otherwise the original will have to be ground to repair the journals where the bearings spun.
 

·
Registered
Joined
·
1 Posts
I've never heard of the weight matching, but as far as Mopar OE is concerned, the pistons are sold as a piston/rod assembly. Pistons/rods are available separately in the aftermarket.

I dont see weight matching being a concern; as long as the aftermarket stuff is built to OE spec it will be fine and will be the proper weight --- be careful here, cheap rods off of amazon are suspect; there are tons of counterfeit parts out there from other countries, especially on amazon etc; that are complete garbage.

The pistons and cylinders will need to be checked for wear as well, these engines are susceptible to piston slap if the pistons are even slightly worn. In my experience, if you are going this deep, I would mic all cylinders, bore as needed, replace all pistons regardless of how many rods need replaced. Any rods you think are still good, just need to check their bores and make sure they are in spec still. Usually there is not an issue with a rod unless there was a spun bearing or oil starvation.

I would suggest having the engine builder swap the rods; since they are press in; unless you are sure you have the proper tools to do it; if you've got a shop press, ok, but its a different process than pressing out a ball joint or bushing, there may be a depth or clearance spec involved---plus an oil clearance spec on the rod-wrist pin.

Be careful supplying your own parts to a builder, generally, if they agree to do it at all, it will void your warranty.
The old school term if you've heard it: "balanced and blue printed" is just that.
Balancing goes hand-in-hand with performance engine building. Balancing reduces internal loads and vibrations that stress metal and may eventually lead to component failure. But is it worth the time and effort for mild performance applications, everyday passenger car engines or low-buck rebuilds?
From a technical point of view, every engine regardless of the application or its selling price can benefit from balancing. A smoother-running engine is also a more powerful engine. Less energy is wasted by the crank as it thrashes about in its bearings, which translates into a little more usable power at the flywheel. Reducing engine vibration also reduces stress on crank/rod bearings, motor mounts and external accessories, and in big over-the-road trucks, the noise and vibration the driver has to endure mile after mile.
Though all engines are balanced from the factory (some to a better degree than others), the original balance is lost when the pistons, connecting rods or crankshaft are replaced or interchanged with those from other engines. The factory balance job is based on the reciprocating weight of the OE pistons and rods. A postal scale accurate to the hundredth or thousandth is all you'd need and there is a plethora of info on the googler about methods and procedure such as finding the lightest piston and rod and lightening the rest to match. Good luck.
 

·
I hit **** with sticks!
Joined
·
38,007 Posts
The old school term if you've heard it: "balanced and blue printed" is just that.
Balancing goes hand-in-hand with performance engine building. Balancing reduces internal loads and vibrations that stress metal and may eventually lead to component failure. But is it worth the time and effort for mild performance applications, everyday passenger car engines or low-buck rebuilds?
From a technical point of view, every engine regardless of the application or its selling price can benefit from balancing. A smoother-running engine is also a more powerful engine. Less energy is wasted by the crank as it thrashes about in its bearings, which translates into a little more usable power at the flywheel. Reducing engine vibration also reduces stress on crank/rod bearings, motor mounts and external accessories, and in big over-the-road trucks, the noise and vibration the driver has to endure mile after mile.
Though all engines are balanced from the factory (some to a better degree than others), the original balance is lost when the pistons, connecting rods or crankshaft are replaced or interchanged with those from other engines. The factory balance job is based on the reciprocating weight of the OE pistons and rods. A postal scale accurate to the hundredth or thousandth is all you'd need and there is a plethora of info on the googler about methods and procedure such as finding the lightest piston and rod and lightening the rest to match. Good luck.
Agree, and in a high performance/high RPM engine I would absolutely be all over it. Never really a concern in an every day driver build; that being said;

If you decide to do it, balancing doesnt involve trying to find new connecting rods and pistons that are weight matched. They are balanced at a machine shop by finding the lightest component and removing metal from the others so they all match, or are within tolerance...not to mention you are talking hundredths, thousandths of a pound as well... Same with the crankshaft, metal is added/removed to balance it in conjunction with the rotating assembly. Depending on the engine they can be externally balanced as well.

Once you buy new pistons/rods is it worth it to have them checked? Sure.

Quality parts will already have the proper weight and it wont be absolutely necessary to dial it in on a daily driver. Can you do it, sure, needed and worth the extra time and expense on a 2.7? Probably not.

Modern engines are much more dialed in balance wise nowadays as well; and if new quality parts are used, you'll be fine. Many GOOD quality aftermarket piston sets will already be a matched set. Rods wont be, unless you buy the Mopar assemblies I mentioned earlier. Will a couple new rods not weight checked adversely affect the performance in a daily driver? Nahh. Even a set wont.

I've had two engines balanced and blue printed; done by a machine shop; one a 383 stroker, the other a 327 out of a Corvette I rebuilt for a customer. It was a pretty good extra expense. Reason? High performance, high RPMS, high horsepower. I've built several modern engines including 2.7's, 3.2's, 5's etc, never once had a concern over balancing; nor had one balanced. Any pistons replaced were done as a set; rods, never replaced the entire set unless it was necessary, always had them checked and machined if needed (bores). Most of the time in a case of a spun rod bearing, only one or two rods needed replacement.

To the OP's question, replace the damaged rods, be done with it. Have a machine shop check the rest. Have them check pistons/bores and crankshaft at the same time and machine/repair/replace as needed. Dont make it more complicated than it needs to be.
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #6 ·
"Don't make it more complicated than it needs to be". Thank You Daytripper, I needed that.
I took the two rods, #3 and 4, that had the spun and worn bearings to a machine shop. The guy took one look and said I needed new rods all around. I didn't have the crank or block at the time but I've gotten it from several folks, including here, to just get a serviceable crank and rods to match it. The shop can get me a crank and rods for a lot less that I can get myself though I didn't get a price but he said $100 to tank the block and hone the cylinders. I'm taking everything to two other shops as soon as I build a proper "cradle" for the block to ride in the bed and get other opinions. Of course, I've got to balance everything to the reality that it's a twenty y/o car. I want to get a new serviceable crank but I'm thinking just replace the two rods that took the stress of bad bearings, albeit for just a half mile, and get the other four cleaned up.
I wrote on another thread that the pistons were very stiff on the rods. Well, I took a proper sized socket and after heating the assemblies in boiling water, and/or propane torch, was able to pound the pins out w/o much trouble. the pins measured within specs. I did that because I wanted to know why they were so stiff. However, the machinist asked if I was going to use the same pistons (not knowing what I did). I told him yes because they look fine. I don't have an issue buying new but that would really start to push the cost/benefit ratio to the edge.
So I'm gonna' visit the two other shops, maybe three, and get other opinions. This is just a family type four-door car and it's driven like one. And I'm dealing with performance engine builders who may not be used to some guy walking in with parts from a "normal" everyday car. I did like the first shop with engine blocks laying all over the place. I want to ask if he happens to have a 396 laying around. I'm planning on redoing the tbi 350 in my Chevy truck after the car is done and planting a 396 in it would be a dream come true in an old school kinda' way. They were "the kind" in my day.
I'll advise what I find out.
As always thanks
 

·
I hit **** with sticks!
Joined
·
38,007 Posts
"Don't make it more complicated than it needs to be". Thank You Daytripper, I needed that.
I took the two rods, #3 and 4, that had the spun and worn bearings to a machine shop. The guy took one look and said I needed new rods all around. I didn't have the crank or block at the time but I've gotten it from several folks, including here, to just get a serviceable crank and rods to match it. The shop can get me a crank and rods for a lot less that I can get myself though I didn't get a price but he said $100 to tank the block and hone the cylinders. I'm taking everything to two other shops as soon as I build a proper "cradle" for the block to ride in the bed and get other opinions. Of course, I've got to balance everything to the reality that it's a twenty y/o car. I want to get a new serviceable crank but I'm thinking just replace the two rods that took the stress of bad bearings, albeit for just a half mile, and get the other four cleaned up.
I wrote on another thread that the pistons were very stiff on the rods. Well, I took a proper sized socket and after heating the assemblies in boiling water, and/or propane torch, was able to pound the pins out w/o much trouble. the pins measured within specs. I did that because I wanted to know why they were so stiff. However, the machinist asked if I was going to use the same pistons (not knowing what I did). I told him yes because they look fine. I don't have an issue buying new but that would really start to push the cost/benefit ratio to the edge.
So I'm gonna' visit the two other shops, maybe three, and get other opinions. This is just a family type four-door car and it's driven like one. And I'm dealing with performance engine builders who may not be used to some guy walking in with parts from a "normal" everyday car. I did like the first shop with engine blocks laying all over the place. I want to ask if he happens to have a 396 laying around. I'm planning on redoing the tbi 350 in my Chevy truck after the car is done and planting a 396 in it would be a dream come true in an old school kinda' way. They were "the kind" in my day.
I'll advise what I find out.
As always thanks
Your still making it more complicated than it needs to be. LOL.

Crankshaft kit, replace rods with spun bearings, check pistons and the rest of rods, if in spec and can be cleaned, reuse; stick with one machine shop; pay them, put it back together, be done.
 

·
Registered
Joined
·
74 Posts
Discussion Starter · #8 ·
Daytripper and Ronbo are absolutely correct. In the meantime I accidently did something to the #5 cylinder wall that is going to add an extra step in this dilemma. BUT I have the shop that'll fix that and re-size/replace the rods, provide crank kit, bearings etc. and clean the block and anything else they recommend.
If any of you all think this drama has gone on too long; you'd be right. With a little luck I'll have it up and running in a couple weeks.
Thanks All
 

·
Registered
Joined
·
1 Posts
Although these three are interchangeable, they must be used in complete sets of the same part number because each part number has a different weight. Connecting rods and pistons are one more example of the need for appropriate reference materials when working on Lycoming engines. forpc.onl jiofi local html
 
1 - 9 of 9 Posts
Top