How would you take the flex from a hollow cam?

[Torquey]

I have been modifying a Ford 4.6L dohc (modular) motor for about a year now. After close study, I conclude that the stock cams cannot withstand the added stress of after market (high pressure) springs. Reason? Hollow cams.

For the mod motor, Ford perfected a method of setting cam lobes on a hollow tube by pushing a steel ball down the center. All Ford modular cams are hollow. All after market modular cams are solid. By clamping down a small amount of resistant cam friction and hand turning the crank, I have watched these cams flex enough to gall the bearings. So, gentlemen, here is my question...

What would be an effective method to stiffen up these hollow cams? Here are some wild ideas:
1) Pour lead down the center.
2) Pour a binary compound down the center (ie epoxy?).
3) Weld a steel rod inside the cam. (This idea worries me since it would probably require the cam center to be drilled before hand... which might re-loosen the lobes.)

I would be most appreciative for any insights here.

Walter Carter, Palm Springs, California

 

[Lou Scannon]

You might look into shrinking the hollow camshaft onto a thickwalled steel tube. Of course the shrink assembly procedure is a ticklish business so I'd recommend doing a lot of research and analysis before proceeding, and be prepared to spoil a few cams before you succeed.

 

[thundair]

What is the inside diameter of the cam shaft?

I don't know anything but the people that do.

 

[Torquey]

It looks to have about 18.5mm inside diameter.

 

[evelrod]

The big question...Why would you want to use the hollow stock OEM stuff given the statement that you are "modifying" the engine ? I don't have an SVO catalog handy (indeed, I have not messed with V-8 stuff in years) but I'll bet it would be a bunch cheaper and safer to just go for after market cams!

I have a bit of practical experience in hollow Ford/Lotus camshafts that tended to break when reground to extreme lift/duration/rates with the attendant high spring rates necessary to keep things from going bang. My solution was to use cams ground on steel billets. Perhaps a slight bit more expensive up front, but satisfactory performance and no breakage in many years of racing.

Rod

 

[BrianPetersen]

My suggestion is to not mess around with the stock camshafts. Ditch them and replace them with something else that will take the stress.

 

[MikeHalloran]

Making the tube solid by any means is not going to reduce the deflection as much as starting with a billet, or otherwise increasing the _outside_ diameter of the shank/tube/whatever.

If you really want to use the stock cam as a basis, I'd insert a steel rod through the center, right behind a ball of strong thickened epoxy which should be able to take up the radial gap. But first look at the deflection equation for a long skinny tube or round bar stressed as a beam to see how little effect it will really have.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Use a new cam with a bigger shaft diameter.

Like mike says, filling the centre won't make a huge difference.

Regards

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[thundair]

This may be a little out there. but I have built thin-wall
wrist-pins (.048") and filled them with 50 modules unistrand prepreg polyamide and with a .927 Chevy wrist-pin the stock one broke at 9800# while mine broke at 17200#.

That being said if it is possible to get uniformity of your windings the full length you will have as much in them as an after market cam although it will be lighter.



I don't know anything but the people that do.

 

[Torquey]

This recession has hit me pretty hard. Four valve after market cams are around 1500 samolians per set. Two years ago I could pay that standing on my head. I no longer have that ability. That's really why I'm interested in getting the Ford cams to perform a little better.

 

[Torquey]

Is anyone aware of a resin/catalyst type substance that sets up really hard?

 

[MikeHalloran]

Plastics are not really all that hard, and 'hard' isn't what you need anyway. You need something with compressive strength in the radial direction and a good enough bond to carry shear as the tube tries to bend.

Least awful low-buck technique I can think of is to sweat-solder a steel round in the hole. Fit it to .002 to .004" gap per side if you can.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

The grout designed to fill water jackets in engine blocks for drag racing might help. It expands a little on curing to create an interference fit and reinforce the bore against expansion from cylinder pressures. It has very good compressive strength. It might help, then again it might crumble and fall out and damage the oil pump and block the pick up screen.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dicer]

If this is for competition, I would think the rules would not allow for any internal modifications, such as after market valve springs. If it is for normal everyday transportation there is no need to do such modifications, as the traffic and speed limits give no reason to develope anymore Power than the factory / manufacture designed the engine to have.
The cost of engineering the dynamics of the valve train to utilize your OEM cams far exceeds the cost of purchasing aftermarket units. The cure for any flexure is larger diameter, and stronger material. Your ideas posted would change harmonics of the system, and may help to some extent.

 

[evelrod]

Walter, you still haven't answered "the big question". Why do you want to take the risk of a total, cataclysmic engine failure by using a modified stock camshaft that even YOU admit is not adequate for the job? I understand the economics of building race engines, I've been doing it for over 50 years. It took me a lot of those years and a lot of treasure to discover the "economy" of using the best parts, regardless of their cost! $1500? That's pretty cheap by todays standards.
What will ONE blown engine set you back?

Rod

 

[Torquey]

Rod, this is not a situation where you throw on the fix and hope for the best. I went through a dozen stock camshafts and measured major deflection in each one. If a solution is found, I won't be measuring any deflection and so, will know the problem is solved. Even so, my gut tells me (as well as helpful posters, thank you) that this problem is not fixable within reason. But since I have many Ford cams to play with, I might give Pat Primer's idea a shot. I like the simplicity of opening one end of a camshaft and pouring in an expanding compound. What's to lose? Does anyone know an internet source for the expanding block filler compound or perhaps a trade name for it?

 

[MikeHalloran]

The flex you describe will probably crack anything like that, and the fracture products will not do the engine any good.

You'd do better to try reaming the bore and shrinking a steel rod into it... but the assembly has to be done very quickly.

Another thing that comes to mind is spacers around the od of the shaft... but they have to split for assembly, retained somehow, and they have to be a close/press fit axially between the cams and the bearing journals in order to be effective... but Comp Cams' shafts are certainly cheaper.





Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I once again stress that this is NOT WITHOUT RISK and will not add much to the beam stiffness, but it will add a little if done right. The product is called Hard Block. It is available through performance engine parts outlets. The price is downright robbery considering it is sand, cement and I think aluminium hydroxide to create the foam for the expansion to create the interference.

Don't try to make your own as the degree of expansion will be critical and their formulation has that worked out.

Once again, even though I suggested it, I don't recommend it. My recommendation is grind a cam on a significantly bigger diameter shaft.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Torquey]

Thank you all for your contributions.

 

[thundair]

Torquey

Check out the specs on this tube which you can slide in with some polyamide high temp epoxy

http://www.graphitestore.com/itemDetails.asp?item_id=1380&prd_id=99&cat_id=34&curPage=1

Cheers


I don't know anything but the people that do.