Camshaft question

[NewZed]

Sorry about the bad info on swapping cams. Pretty sure I've seen accounts where people have done it and survived but apparently the odds are against it.

 

I took a look at some other sources, the FSM and Monroe's rebuild book, and if you put all of the advice together, the safest route is to just get another head complete with untouched cam, rocker arms, lash pads and cam towers (never unbolted - misalignment) and install it as a complete assembly. Apparently, the cost of new or reground rocker arms is the big killer if you want to do a cam swap the right way.

 

Seriously, you could probably find a used engine for the cost of a spray bar assembly. Used car economics don't make a lot of sense sometimes.

 

Here's one for $50 with a few extra parts, but a little far away - http://forums.hybridz.org/index.php/topic/105590-for-sale-280z-l28-engine-transmission-50/

[theczechone]

Thanks guys for the great info, I'm actually going to look at a parts car to buy this weekend so I'll decide what to do than. The cam is stock, and has Japan stamped on it as a stock one should. I have looked around the spray bar and the left "bridge" on the spray bar is actually bent, and has about a millimeter of clearance to the actual cam. I'd like to get a spray bar from larry but at that price, I could buy a whole used engine to drop in like you said.

I was also thinking about straightening the bent "bridge", tapping it, and get oversized aluminum tubing that would thread in... i'll go see what I can find at the local Lowes. I feel like I'm going to get flamed for even thinking about that, but it's just another possible solution. It just seems too simple to be that complicated... I don't want to deal with replacing a head, cam or an engine for now ... just want to get this one in running condition.

[Gollum]

It's a tedious but necessary procedure; anyone who says changing cams on a z is quick and easy is NOT doing it right.

 

Let me clear about my previous post, as it's in conflict of this statement that I half-agree with.

 

The context of my last post was regarding an engine that's going to be replaced anyways, and also lower HP. I agree that checking wipe patterns is always good procedure and should be done, especially when changing to a higher lift/duration cam grind.

 

But to play devil's advocate here, I'm 99% sure when these motors were originally built wipe patterns weren't checked. Granted, all components had to be QC'ed and made sure they were within spec before assembly.

 

All that said, I personally feel that unless you're trying for a fairly hot setup (lets say 200+whp), then if you had a running P79 head (as example) and you pulled an entire P79 from another engine, there's no reason you shouldn't be able to number the cam towers and pads and swap over the cam, check valve clearance and be good to go. Yes machining the surfaces smooth again then doing wipe pattern checks and adjustments is a "good idea". I would never say it wasn't. I just personally don't find it "necessary" for everyone out there.

[NewZed]

Sorry about the bad info on swapping cams. Pretty sure I've seen accounts where people have done it and survived but apparently the odds are against it.

 

Quoting myself here for a followup - I came across the thread about reusing rocker arms, over on zcar from norm(The 12 sec Dual SU Dude). Interesting stuff, the relevant post is about half way down the page, search "how to resurface rocker arms" to find it.

 

http://www.zcar.com/car_talk_forum/part_3_5_years_drag_racing_trialstriumphs_and_tech_info_822277.msg822277.html#msg822277

[Tony D]

But to play devil's advocate here, I'm 99% sure when these motors were originally built wipe patterns weren't checked. Granted, all components had to be QC'ed and made sure they were within spec before assembly.

 

During assembly at the factory the machining tolerances were taken to five places to the right in millimetres on precision Mitsui Seiki Machining Centers as a result of Demming-Inspired SPC assembly standards. Because of the insanely-tight (compared to comparable production US Machining Practices at the time) manufacturing tolerances MAINTAINED the wipe pattern could be ENGINEERED INTO the assembly. Have you EVER removed original stock lash pads? They are all the same size. They had a manufacturing process operating within statical control and as-such di not require a check.

 

The wiping of the lash pad is a Field Service Procedure as variability in valve seat machining by non-OEM production machinery is not guaranteed. A machinist might be sloppy. That is why they have you check.

 

To illustrate the tolerances issue endemic at the time Ford had a 50% failure rate on (i think) C6 transmissions one year in the late 70's. When Dearborn investigated, they found they had two vendors: normal chain, and about 50% farmed to JATCO. on examination, they found there were NO failures of the JATCO-Supplied units, and a 100% failure rate on the normal supply chain vendor units.

They disassembled the normal units, and found everything was "within specification"- yet they failed.

They pulled in some JATCO units and when disassembled they didn't find things "within specification" they found them spot-on "nominal" Transmission to Transmission the components were measured to be EXACTLY the same. There was NO range of deviation. They were, using the measuring tools available to Ford at the time, the same, identical. JATCO supplied documents showing variability in metric equivalents out in the fourth and fifth decimal place. Ford was going four places right using INCHES (1/10,000 of an inch!) this was a stated reason for Ford being one of the first manufacturers to adopt SPC in the Demming Method in the USA during that time period.

 

It all goes to standards of machining and variability in the process. It may "Work", but...