Resolved 420A Cam Cap Replacement

[BLACK'98DSM]

Can I interchange cam caps? The ones that go to the head I just built are fried. And it would be a shame to not use that head because of the cam caps not matching. I have multiple sets of 420a cam caps so if I can use another set then great.

 

[DirtMcGirt]

The caps are specific to each head, however you could look into the cost for a machine shop to add material where needed, and do what I believe is called a line bore. If it’s possible and cost effective, that may your only option since you can’t use the proper caps.

 

[motomattx]

The caps are part of the head assembly, it might be cheaper to find another good casting then trying to have what you have machined, if the caps are junk the journals in the head have to have damage also.

 

[BLACK'98DSM]

Well I had the journals on the head machined, I just forgot to give them the cam caps as well. I'm concerned about machining the head yet again, it might take away too much material.

Really hoping it works out though. I have many hours and a bit of money into this head.

 

[VelocitàPaola]

I'm not sure what they could've machined without the caps...

 

[BLACK'98DSM]

I'm not sure what they could've machined without the caps...

You must be logged in to view this image or video.

You must be logged in to view this image or video.

 

[VelocitàPaola]

But they never asked for the caps? What good is it to have just half of the bearing surface machined?

 

[Mello]

What type of machine shop would machine half a bearing in the first place. I'd think any competent shop would have spoke up & raise a red flag at minimum, or more so refused to do it until the caps were included.

 

[BLACK'98DSM]

Yea that's not the only issue I had with this shop. They did a damn good job milling the head and resurfacing the block, but were terrible on all other aspects.

 

[BLACK'98DSM]

I wanted to add a little clarification, updates and additional information. Especially since this topic has come up again, and I'm sharing the link to this thread.

1: You should not interchange the cam caps between different cylinder heads. While you CAN, it will not end nicely. I actually did that some time after making this thread with a different cylinder head. Everything seemed fine at first, but within 200 miles some strange "rattle" noise appeared. At the 2000 mile mark, I deemed the cylinder head and one of the camshafts unusable. The noise was very loud and exaggerated, as if the camshaft was literally bouncing around. And I could feel a loss of power due to improper valve lash (which should be zero on a 420A).

2: I did speak with the machine shop in the following weeks after making this thread, to understand how or why they only machined the head journals without my cam caps. They said that they actually had a 420A head laying around, so just temporarily installed those cam caps to do my machining. I had to sit on that thought for a while, but it pissed me off. Definitely not what I wanted or needed and I had to have my head line bored for that reason. It was partially my fault for not bringing everything required for proper work, however they should have immediately mentioned this and not worked with someone else's shit.

3: As already stated, EVERY head is cast, cut and drilled slightly different. These slight differences are actually a huge difference when it comes to the camshafts riding in the center bore, having proper valve lash, and proper lubrication. An extra 0.010" of offset will wear down quickly and have the cam riding in an oval rather than a perfect bore. Which will wear down the cam journals and the rocker arms soon after.

All in all, there's no reason to use cam caps from a different cylinder head, and especially not to install your cam caps in the wrong order. The manufacturers include directional arrows and sequenced numbers for a damn good reason. Follow the proper installation instructions to avoid any engine damage or noise!

Also, the majority of this information applies to ALL engines that this forum is based on. 420A, 4G or even 6G. Hell this has applied to engines for many years.