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Q: Camshaft interchangeability 4.2 & 4.0 |
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knobbler
AMC Apprentice Joined: Sep/13/2015 Location: Seattle Status: Offline Points: 171 |
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Great thread! Thanks for sharing. That helps lend a little more anecdotal input on the fuel pump lobe question for the renix cams. Looks like the safe bet would be to assume that it wouldn't be there at this point, given the stock rotation has bound to have cycled out anything that still had them by this point. Much appreciated!
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nudhistbudhist
AMC Apprentice Joined: Sep/13/2019 Location: AB, Can Status: Offline Points: 178 |
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Where did you make the bore measurements? Did you make them in a few places up and down? Most of these engines have seen quite a few miles so I'm surprised if it's not worn. Not impossible tho I suppose
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Greg
1980 AMC Spirit GT 4.0/ax15 swap Ford 8.8 |
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knobbler
AMC Apprentice Joined: Sep/13/2015 Location: Seattle Status: Offline Points: 171 |
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Yep. 12 measurements total; 3 width measurements at each of 4 equally spaced levels down the depth of the cylinders, in between the ends of ring travel in the stroke, starting crossways to the length of the block, turn 120°, then turn an additional 120° from there (procedure described in the engine overhaul manual). Then I took a separate measurement on each cylinder to check piston/bore clearance (crossways, at a depth of 2.3125"), and it was there where things went sideways haha Long/short, I was getting a lot of bad reads, partly due to lack of experience with the bore measurement instruments (hard to develop that "feel" with telescoping gauges. Thought the bore indicator would be more forgiving, and it was — just not as much as I needed). Turns out a trip to the machinist is unavoidable, which is a bummer because of cost, but more because of backlog. I have one who I might be able to get the block to on Monday, but everyone else was booked out for months (one has 75 motors in queue and doesn't expect to have an opening until December!). When all was said and done and I could get good reads that I had strong confidence in, I had one cylinder that was maxed out for out of round AND taper allowances (0.001 out and the same for taper). Yeah, it was "within tolerances", but not too long after it gets fired up and wear is put on it, it'll be leaving the long blue smoky tail. But it was really the measurements I got for piston/bore clearance that did it. . . Man. Not a single cylinder measured out to under 5 thou out! At that point I had to bite the bullet. Needs a bore & hone and some oversized pistons & rings. Thinking it'll prob need 2 over, maybe more, but I'll trust what the machinist has to say on that.
Edited by knobbler - Jun/14/2023 at 7:53pm |
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nudhistbudhist
AMC Apprentice Joined: Sep/13/2019 Location: AB, Can Status: Offline Points: 178 |
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I'm currently an hour and a half from home at a training class for Detroit diesel and my spirit file (which I admit to forgetting about) is home. Of the top of my head, I think I only paid about 36 bucks cdn a hole for piston boring. If you're not going for big big power, maybe a set of hypereutectic pistons can be had? +.020" I think is fairly common
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Greg
1980 AMC Spirit GT 4.0/ax15 swap Ford 8.8 |
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farna
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19676 |
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Glad you're going to bore it! I was going to ask how long you plan on keeping the vehicle, as not boring now would probably get you 10-30K (depending on all sorts of things!) before it needed it and it would have to be torn down again. Hyper pistons would be nice and are available, but for a basically stock rebuild there's no need. Still, I'd go for them if price isn't much more than standard cast replacements. Several Jeepers I know (only on internet though) use the 4.0L cam as a slight upgrade from a stock 258 cam. Can't say if it's enough to notice, but cost is about the same as a stock 258 cam so why not a slightly better one?
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Frank Swygert
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knobbler
AMC Apprentice Joined: Sep/13/2015 Location: Seattle Status: Offline Points: 171 |
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I didn't even think about a set of hyper pistons — not a bad idea. . . A quick glance shows there's some options out there which can be had for little to no real difference in price on a set-vs-set basis. I'm gonna have to bust out the adding machine and my green bean counter visor to see what it would look like overall, since there's a couple master rebuild kits I've been looking at which offer a pretty solid savings over the lowest price combos I was getting from rockauto, but they all come with OE-spec pistons, so the difference could end up being a lot more than it might immediately appear. Still definitely worth considering!
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knobbler
AMC Apprentice Joined: Sep/13/2015 Location: Seattle Status: Offline Points: 171 |
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I plan on keeping the bird going for as long as it's willing to keep working for me. I've never had a vehicle as eager to please and as stubborn about keeping going as this wagon has been. We know each other pretty well, compliment each other nicely, and know what our respective tics and pet peeves are. Kinda like an old married couple haha But yeah, that was pretty much my thought on getting it bored versus just making do with the bare minimum for now and having to go back and do everything all over again (and then some, most likely) in what's really a short length of time when all is said and done. Putting off doing something the right way just means you're gonna have to do it at a time when it's even more of a hassle. Gotta be kind to future me, because I've been bitten by past me too many times to keep acting like that guy.
That's kinda what my thought was, but the considerably lower price was what really made the idea shine. Switching to an electric fuel pump because of a lack of a pump lobe isn't really that big of a problem; it could even save me some bigger headaches down the line, seeing as failure with a mechanical pump isn't just a breakdown, but a breakdown AND an oil change (and would happen right after I put fresh stuff in, because that just seems to be the way it goes). I'll just have to sit down and do some cogitation like with the pistons as far as what the real price would end up shaking out to.
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nudhistbudhist
AMC Apprentice Joined: Sep/13/2019 Location: AB, Can Status: Offline Points: 178 |
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I forgot you were building a 4.2 sorry. The hyper pistons I bought were +.030" for 4.0
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Greg
1980 AMC Spirit GT 4.0/ax15 swap Ford 8.8 |
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