Advice on rods after melting pistons

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  1. #1

    Default Advice on rods after melting pistons

    So I picked up a low mile cobra engine that was rebuilt with the cheapest Taiwan special pistons I've ever seen. It had melted 2 pistons and blew a small hole through both of them. When the piston blew through, it deposited a small amount of melted piston on 2 of the rods as you can see in the photos I've attached. Are these rods salvageable? I don't see any discoloration from heat. I'm assuming I could take a brass wire wheel to these gently and it would take the deposits right off, then just have a shop rebush and check them.

    Also, the motor had a mismatched set of manley rods. 6 stock cobra rods, and 2 manley H-beams that look basically identical and got sprayed with melted piston. I got the short block so cheap that even if I NEEDED 2 new stock replacement cobra rods, I'd still be in the black.

    Basically would this set be safe to run of okayed by a machine shop? Any advice? Thanks

    Sent from my SM-G975U using Tapatalk

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  3. #2

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    Robert,

    If the rod has not been overheated where the aluminum spray contacted it, then it is likely OK to re-use with good practices like clean up, pin bushing replacement etc. Aluminum has a melting point od 1221 ˚F. In a cylinder under pressure you can blow a hole through a piston probably somewhere son n the 900 -1000 ˚F range. There will be some cooling (not much) as the aluminum spray passes through the air space between the underside fo the piston and the rod. Bottom line for a race engine I would throw those rods out. The potential risk for a number for different mechanical failures is not worth the few dollars yo will save.

    There are any number of replacement alternatives available to you today. For a maximum effort engine I would run something like the Manley Pro I-Beams or the Wiseco Boostline rods. Here is what the Manley rod looks like;

    Name:  Manley Pro I-Beam.jpg
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    And this is what the Wiesco Boostline rod looks like;

    Name:  Boostline.jpg
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    Both are stunningly good choices. The Wiesco's are about half the Manley price. I have a personal bias for the Wiesco's because of the big end design. Wiseco took some cues from the high end F-! rods designers that use a similar style big end configuration to more evenly load the upper rod bearing.

    For mere mortal engine builds with under 30 psi of manifold boost I would give serious consideration to the new Manley Hi-Tuff H-Beam rods. Manley has added material to the beam section and reinforcements around the pin area. The rods as Manley states in their materials fit between the standard H-Beam offerings and their Pro series I-Beams.

    This is what they look like;

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    Pricing-wise the rods will play out pretty much like this at Jegs or Summit;

    • Manley Pro I-Beam ..... $2,100
    • Wiseco Boostline ........ $1,240
    • Manley Hi-Tuff ............ $870


    For all but the take no prisoners crowd the Hi-Tuff alternative makes a lot of sense, especially when you conducer how well the "normal" Manley H-Beams have performed over the years.



    Ed
    Last edited by eschaider; 04-30-2020 at 11:24 AM. Reason: Fixed Broken Pic Link

  4. #3

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    Thanks for the great advice. I'll get them checked by a shop and recondition them. These won't be going in a max effort race engine so if they check out I won't worry. If the 2 mismatched ones were the victims of the spray I'll grab 2 stock replacements as it'll please my OCD of all the rods being identical.

    For my max effort engine I am definitely going with the Wiescos. Love the design and I know you've been touting them as a great choice for a while now.

    Sent from my SM-G975U using Tapatalk

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  6. #4

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    What I didn't say that I should have is, when you replace one or more rods in a set you will usually get a weight difference end to end and in total that will require either lightening the new rods to the older rods weight or lightening the old rods to the new rods weights. When this is done the rods being lightened need to have material removed that requires machining, siding or grinding. H-Beam rods do not have pads on the big and small end to facilitate weight balancing. that means you need to cut on surfaces and areas of the rod that you should not be fiddling with. When Manley sells you a complete set they typically come in within a gram or so.

    Don't let your visual OCD trump your what should be your operational, physical OCD. The physical and operational realms are the most important. The aluminum spray on the top and beam sections of the rod can cause the metal to change properties which makes for an accident looking for a place to happen. That place is usually inside your engine.

    Sell off your used set for whatever you can get for them and put the money towards a new set of rods. The adder you will have to contribute to get a new set of Manley's H-Tuff rods will be marginally more than you will pay to buy new replacements and rebalance everything or properly test and recondition those old H-Beams and then rebalance the whole set. Removal and replacement is the smart way home. Your plan involving repair or replacement of the two dead soldiers is a formula for unhappiness.


    Ed

  7. #5

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    Wow, can't believe that's the current price for the Manley I beams. I've been using them for years and the last set I bought new was around 1400 bucks, granted that was a few years ago. If that's the current new price, I won't be using them again. I'll move on and give Molnar rods a shot as I've seen guys running them successfully in max effort engines and they run under 800 bucks a set.

  8. #6

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    Quote Originally Posted by Helomech74 View Post
    Wow, can't believe that's the current price for the Manley I beams. I've been using them for years and the last set I bought new was around 1400 bucks, granted that was a few years ago. If that's the current new price, I won't be using them again. I'll move on and give Molnar rods a shot as I've seen guys running them successfully in max effort engines and they run under 800 bucks a set.

    I think the 300M Manleys came out after your rods were purchased, Joe. Manley still offers a 4340 version of the I-Beam rod that can be had through distribution for around $1,460. the difference is the material and the profiling of the rod. The $2K Manleys are made from 300M steel and weigh a bit more according to Manley. Manley lists the 4340 steel I-Beam as a 670g rod and the 300M rods as 695g rods. The weight difference is attributable to increases in cross section where failures hand perhaps previously occurred.

    The difference in mechanical properties between the heat treated, vacuum degassed 4340 like Manley uses in their $1,260 offering and the 300M material they use in their $2K rod offering is a distinction without a difference. The additional material added to the $2K connecting rod profile is not. The 300M distinction gives Manley a way to charge measurably more for the rod than they could if they just enhanced the profile of the $1,460 rod.

    While Molnar rods ar very nice rods the are my fourth pick in the rod selection pecking order. Very nice/ good design, comparatively light weight and strong. There is however a distinct difference in mid beam strength of the four rod offerings. The I-Beam rods have historically had larger (and therefore stronger) beam sections. Second in line have been the standard Manley H-Beams. If you compare a Carrillo to a Manley and measure the beam dimensions with a dial caliper you will find it it measurably beefier than the Manley offering—it is also back into the $2K price range.

    The real sleeper in the Manley line up is their H-Tuff rod. The blades and beam section have been substantially improved and appear to be even beefier than the Carillo rods they copied. Manley lists the weight of their standard H-Beam rod as 605g. they list the weight of their standard weight 4340 Pro Series I-Beam rod as 675g and their 300M Pro Series I-Beam as 695g. By contrast they list the weight of their new H-Tuff H-Beam rod as 685g. Tom Molnar lists the weight of his Modular PWR ADR rods as 653g. The Wiseco Boostline rod comes in at surprise, surprise 695g.

    I think it is impossible to pick a bad rod out of this line up. In the end it comes down to a personal preference and a budget consideration. The two budget winners ar the Molnar and H-Tuff offerings. At the top of the hill are the $2K 300M Manleys and the $1,240 Wiseco Boostline offerings. Like all of us I have prejudices in connecting rod selection. If I were buying today, my preference would be the Boostline rods for a top end pick. They have comparable beam strength to the $2K Manles and they also incorporate a beam geometry similar to some high end F-1 connecting rods that helps to more uniformly load the top rod bearing. In a selection where I am looking for the most bang for the buck, I believe the H-Tuff rod is simply unbeatable especially at its $870 price point.

    I believe it is all but impossible to pick a "bad" rod out of the line up. The important consideration in selections of this type is that you are happy with your choice. If you are, it really doesn't get any better. These choices really do come down to a matter of beauty being in the eyes of the beholder — they are all that good!



    Ed
    Last edited by eschaider; 05-05-2020 at 04:25 AM. Reason: Spelling and Grammar

  9. #7

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    The pistons show excessive skirt scuffing, so something else may be going on.
    The oil residue on cardboard is unusual. very high wax content?
    Please advise what oil was used, so I never use it.

  10. #8

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    Quote Originally Posted by Power View Post
    The pistons show excessive skirt scuffing, so something else may be going on.
    The oil residue on cardboard is unusual. very high wax content?
    Please advise what oil was used, so I never use it.
    Only piston scuffing was on the pistons which leaned out, and that oil residue is from cosmoline which was sprayed on the block for long term storage.

    Sent from my SM-G975U using Tapatalk

  11. #9

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    Cosmoline-Yeah, that makes sense. It is mostly wax with carrier.

  12. #10
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    Quote Originally Posted by Power View Post
    Cosmoline-Yeah, that makes sense. It is mostly wax with carrier.
    It is most likely LPS-3. LPS makes 3 products and #3 is the best for long-term corrosion protection. After the volatiles evaporate it leaves a waxy material which is a perfect rust preventative. I have boiled, bare sheet metal oil pans in the garage coated with LPS-3 15-20 years ago with no sign of rust. I am not connected to LPS at all.

  13. #11
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    Quote Originally Posted by eschaider View Post
    I think the 300M Manleys came out after your rods were purchased, Joe. Manley still offers a 4340 version of the I-Beam rod that can be had through distribution for around $1,460. the difference is the material and the profiling of the rod. The $2K Manleys are made from 300M steel and weigh a bit more according to Manley. Manley lists the 4340 steel I-Beam as a 670g rod and the 300M rods as 695g rods. The weight difference is attributable to increases in cross section where failures hand perhaps previously occurred. (edit . . . )
    Excellent summation of the various options, Ed. Many thanks . . . it was quite helpful.

    I am assuming all stock rod lengths. But if one needed a shorter or longer rod (i.e., a custom length other than stock) which one of the manufacturers would be easiest to work with? I have been considering Crower as well. Your thought's?

  14. #12

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    Because of the block deck height and the engine stroke there is little or no wiggle room for rod length changes. If you increase the rod length you run the wrist pin into the ring package's oil ring land and will need to use a oil support rail for the oil ring. At the same time the space you used for increased rod length removed the space you needed for an expanded ring package for a supercharged application.

    If you shorten the rod the piston will hit the crank counterweights when it is at BDC unless you shorten the piston skirt or reduce the diameter of the crank counterweights. If you shorten the piston skirt you increase the rocking motion of the piston in the bore reducing ring seal, increasing blowby and reducing power. If you decrease the diameter of the counterweights, the crank will require tungsten style heavy metal to rebalance and that will be a $500 or so proposition to rebalance the crank and you still hav et piston rocking problem — your wallet is just $500 lighter.

    The only different rod length that has been commercially offered is the Saleen rod Ford used in the 5 liter Saleen engines. That rod was designed to be 5,850 inches vs the standard 5.933 inch 4.6L rod. The Saleen rod also uses 2.0000" diameter SBC sized rod journals which your crank does not have. There are any number of custom rod manufacturing shops that will make anything you ask for. You should be careful when you take on the role of design engineer. You could design something that can not be used.


    Ed

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