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Aluminum rods hitting cam

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Aluminum rods hitting cam

Postby demented » Sun Feb 10, 2013 8:12 am

Ok I was just trial fitting my rotating assembly and I ran into a problem with my aluminum rods hitting the cam lobes. All the rods on the passenger side of the block hit the opposite intake lobes of the cam. The combo is a merlin .400 raised cam block, 55 mm cam, and a 5.375 stroke crank with GRP 5500 series rods. I'm thinking of sending the rods back to GRP and having them cam cut for the clearance but I am wondering if I am looking at the wrong part for the fix. Should I be looking at the cam instead. I would rather take material off the cam and make it a slightly smaller base circle than remove material off the rods. I really dont want to give away any cam stiffness as I did spend the money for the 55MM cam setup. I have been thinking of getting a different cam anyways because I wanted some more lift out of it anyways. maybe sending it back and getting the cam reground. Any opinions?
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Re: Aluminum rods hitting cam

Postby Bad Hombre » Sun Feb 10, 2013 8:18 am

What part of the rod is hitting the cam. Is it where the bolt come thru the rod?
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Re: Aluminum rods hitting cam

Postby demented » Sun Feb 10, 2013 8:22 am

Yes but the big end of the rod is much beefier than normal aluminum rods. The bolt DOES NOT come thru the other side so its not the bolt that is hitting. This was a new series of rods that GRP made for long stroke motors and nitrous. They are much beefier than the previous 5300 series rods that I got from them in the past. When I asked at the time of purchase to have the rods cam cut, Woody at GRP said they can do that but don't recommend it on any rods.
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Re: Aluminum rods hitting cam

Postby Bad Hombre » Sun Feb 10, 2013 8:28 am

Is changing the cam going to work? How much of the rod is hitting. Do not cut the rods. I would look into a different set of rods. I would give MRP a call just to see what they have to offer.
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Re: Aluminum rods hitting cam

Postby Strange Magic » Sun Feb 10, 2013 10:16 am

I'm thinking of sending the rods back to GRP and having them cam cut for the clearance


They won't do this process anymore. It's more or less a liability type of issue and they don't want any blame to start spreading around the internet if a rod should break thereafter.

If your building something that large, than you should have access to a Bridgeport.

Cam cutting a GRP right here:

Image
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Re: Aluminum rods hitting cam

Postby wyrmrider » Sun Feb 10, 2013 10:22 am

looks as if you might be GRP's beta tester
work with them on these new rods
are these cap screws?
nothing to hurt removing some materiel at the outer edge where the bolt would come through
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Re: Aluminum rods hitting cam

Postby Strange Magic » Sun Feb 10, 2013 10:24 am

Do not cut the rods. I would look into a different set of rods.


If i'm not mistaken, your the same guy that wrote this below, and I find it very ironic that you obviously do not build engines and have some poor mis-leading advice as well on the subject.

Franco, dont be fooled by people the post pics and video`s. It does`nt prove anything.


When you build 598,'s, 615's, 632's and larger, most all engine builders know it is customary to cam cut. It's done all the time in the industry. Usually only 4 rods, sometimes all. When you design these things, camshaft and base circle should be taken into consideration as well. Your heel should be right at, if not into the core/barrell. At or into the core requires the area right and left of the heel to be dressed, very important.
Last edited by Strange Magic on Sun Feb 10, 2013 10:41 am, edited 3 times in total.
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Re: Aluminum rods hitting cam

Postby demented » Sun Feb 10, 2013 10:26 am

I do own a bridgeport of my own. The thought never crossed my mind though. I would be worried about taking too much off. Alos I would want the rods rebalanced anyways but I guess I could do that too. Milling the rods myself is definately something I could consider since I do know where I need the material removed. Did you make a jig to insure that all 8 rods would set up the same way?
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Re: Aluminum rods hitting cam

Postby Strange Magic » Sun Feb 10, 2013 10:31 am

It's so minimum, that you should not have to rebalance. You should have an over in it anyway. 3 grams per cc.

Did you make a jig to insure that all 8 rods would set up the same way?


Seen right in the picture, your sweeping that area and skimming off. You move the table one way, thats why the rod is not 90 to the table.
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Re: Aluminum rods hitting cam

Postby Old School » Sun Feb 10, 2013 10:40 am

What is the minimum clearance you want ot see between the cam and rods? How much difference for steel and aluminum?
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Re: Aluminum rods hitting cam

Postby Strange Magic » Sun Feb 10, 2013 10:42 am

You can get away with .050

I have many of my own designs with GRP, it allows simplicity when it comes to situations like this. It also allows for a stronger and lighter rod in many cases. For some very few that might doubt, you can call Brian to ask, but don't expect him to disclose information on anything other than what is customarily offered. There are many teams with their own issued part numbers, many create a rod that best suits there needs and they creep up on what they would consider there own rod selection from years and years of working with them. There are very few quality companys in this industry, GRP is second to none in there quality and customer support. Even though GRP works directly with the public as well as race engine shops, sometimes it might be in your best interest to get a hold of a builder that they can recommend, that can help you better understand what your doing, or what your looking to achieve.
Last edited by Strange Magic on Sun Feb 10, 2013 10:53 am, edited 2 times in total.
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Re: Aluminum rods hitting cam

Postby Dave Koehler » Sun Feb 10, 2013 10:49 am

Change cam timing? or at the least double check it before panic whittling. Might want to compare #1 and #6 timing.
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Re: Aluminum rods hitting cam

Postby demented » Sun Feb 10, 2013 10:59 am

I did that already Dave. I cvheck it a couple diifferent ways from 8 degrees retard to 8 degrees advanced. I don't have the numbers in front of me but it did make a difference on when they hit but the still hit each time
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Re: Aluminum rods hitting cam

Postby demented » Sun Feb 10, 2013 11:04 am

Strange Magic wrote:It's so minimum, that you should not have to rebalance. You should have an over in it anyway. 3 grams per cc.

Did you make a jig to insure that all 8 rods would set up the same way?


Seen right in the picture, your sweeping that area and skimming off. You move the table one way, thats why the rod is not 90 to the table.

So how much material would be a good starting point to remove? If we are lookingh for a target of .050-.060 clearance.
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Re: Aluminum rods hitting cam

Postby bill jones » Sun Feb 10, 2013 11:45 am

USED A 6 INCH DIAMETER SINGLE POINT CUTTER.jpg
SETUP FOR HOLDING RODS.jpg


-here's a couple of pictures of how I locate, hold, and clamp the big end of the rod.

-I use a 6" diameter sweep on a single point flycutter to clean the interference point on the rod.

-This was on a 632 BBC---seems like I only had to touch maybe 2 rods which has to do with the particular firing order.
--------------------------------------------
-For sure the cam needs to be installed and degreed exactly how you intend to run the engine.

-and where most guys are running a Jesel belt you also have to install the entire loaded valve train for mock up and run the engine forward AND backwards while checking for interference.

-the Jesel belts I have seen can momentarily stretch something like 8 degrees when you first start to rotate the engine when you have 1000# of spring pressure resisting the cam rotation---and if you ever happened to need to rotate the engine backwards for any reason the cam lobes can interfere because of the belt stretch.

-personally I would not worry much about the balance of just two notched rods--but many guys would go thru the entire rebalance ordeal.
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