New cam in old cam tunnel.

Say you have an I4 OHC engine with an aluminum head, and flat cam follower rocker arms:  

I know that if you put in a new cam, you also have to put in new rocker arms, so that the cam and rocker arm cam followers mate in together. Mixing old and new would ruin the cam. 
 
My question is, since the cam journal rides directly on the aluminum of the cam tunnel in the block, would a new cam in old cam tunnels ruin the cam in the same manner?

Thank you. 

I really hate this design, no bearing to service. When the aluminum wears out the part is basicly junk. I'm sure there is some really expensive way to repair a wasted surface if needed badly enough. 

Anyhow, if the surface looks ok, just oil it up and assemble. What else can be done?

I always figured it's because the lobes are bearing a lot more direct pressure from the rockers, where the cam bearings are sitting on a film of oil and the load is more distributed.  

Gearheadotaku (Forum Supporter) said:

I really hate this design, no bearing to service. When the aluminum wears out the part is basicly junk. I'm sure there is some really expensive way to repair a wasted surface if needed badly enough. 

Anyhow, if the surface looks ok, just oil it up and assemble. What else can be done?

If the cam journals are in the block, a guy could bore the cam tunnel oversize and install conventional cam bearings.  But that would cost money and require a machine shop with knowledge of this specific application.

If the cam journals are in the head, cut the cam caps short and then rebore to factory spec.

If the journals are good visually and measure within spec, install the new cam and send it.  

Btn74 said:

Say you have an I4 OHC engine with an aluminum head, and flat cam follower rocker arms:  

I know that if you put in a new cam, you also have to put in new rocker arms, so that the cam and rocker arm cam followers mate in together. Mixing old and new would ruin the cam. 

No you don't.  OHC is fine for reusing rockers.

It's only for pushrod engines with tiny little lifters that spin in the bores, and tiny little lobes on the cams, and very high loads thanks to the heavy springs on the valves, where you have to keep the lifters and cam mated.

Finger followers in an OHC engine is super easy on parts and you don't really eat through hardening.

Pete. (l33t FS) said:

Btn74 said:

Say you have an I4 OHC engine with an aluminum head, and flat cam follower rocker arms:  

I know that if you put in a new cam, you also have to put in new rocker arms, so that the cam and rocker arm cam followers mate in together. Mixing old and new would ruin the cam. 

No you don't.  OHC is fine for reusing rockers.

 

 

 

Gotcha, thanks.  

But, it does make me wonder why OHC engines with flat cam followers still need the special break-in procedure with high zinc oil. Is that just like an extra precaution for a good break-in?

I have never heard that for OHC engines.  

What's a flat cam follower?

In reply to Peabody :

I'm not sure if that's the proper term for them, but the part of the rocker arm end, that rides against the cam lobe, is just a flat surface, not a roller.  There's no separate tappet involved.