If Magnums used hyper pistons, it's news to me.
piston questions
- Thread starter volaredon
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junkyardhero
Well-Known Member
i think you're picking fly **** out of pepper here.
you're not building a street/strip motor, you're not doing burnouts, you're not hunting 10th's or trying to eek out MPG.
the stock magnum bottom end has proven itself both capable and durable enough for your application, why not go with that? one of the benefits of the stock mag pistons is the design: the top ring land is nowhere near the crown and the bottom is fully clear of the pin boss. on those 405's the top is clipped by the valve relief and the bottom shares with the pin boss. not for me, so siree, not on a build like this.
you're worried to death about the CR, yet you only want to run 87. i'd stop fretting about it. also, the newer motors were built a bit better than the older stuff with better materials, better machining, tighter tolernces and more attention to detail.
i think @TT5.9mag gave some solid advice. screw it together stock, bump the cam up one size with a custom grind (don't buy no junk off the shelf) get a good dual plane manifold and roll.
you're not building a street/strip motor, you're not doing burnouts, you're not hunting 10th's or trying to eek out MPG.
the stock magnum bottom end has proven itself both capable and durable enough for your application, why not go with that? one of the benefits of the stock mag pistons is the design: the top ring land is nowhere near the crown and the bottom is fully clear of the pin boss. on those 405's the top is clipped by the valve relief and the bottom shares with the pin boss. not for me, so siree, not on a build like this.
you're worried to death about the CR, yet you only want to run 87. i'd stop fretting about it. also, the newer motors were built a bit better than the older stuff with better materials, better machining, tighter tolernces and more attention to detail.
i think @TT5.9mag gave some solid advice. screw it together stock, bump the cam up one size with a custom grind (don't buy no junk off the shelf) get a good dual plane manifold and roll.
A big part of the problem with whether to/not to is the increased lack of automotive machine shops around here, I don't know if any within a couple of hours drive that "for sure" offer that service, there are a few machine shops within that radius that I've used, and none have offered to balance anything that I've ever brought in so all I can do is assume they don't. The 2 closest to me can polish a crank, but can't machine them, both have to farm them out that need cut down.
The last several car/truck cranks I have had haven't needed ground undersized but it seems like I can't send them a crank out of a single cylinder Kohler that doesn't have to be ground...
If I knew of someone who balanced engines I could call and get at least a feel for how much it would add to the cost of a rebuild.
Ido agree, it can't hurt, and will probably add to longevity of a build but I can't not work on engines because I can't find a shop that balances them if that makes Sense
And yes. For the cam I already figured on sending one to Ken at Oregon. Which brings another question. I want to run a mechanical fuel pump. I know I have a a couple of magnum cores to send in. They're already a roller cam. I think I have an old LA cam somewhere in my stash so I won't need the Hughes cam extender for the eccentric. Can an original flat tapper cam be reground into a roller cam
My point was from a financial standpoint. He's had one failure. If he's going to BUY pistons (he may not) but if he IS, it's nonsense not to put a couple hundred more toward it and get forged. ...and that's from a cheapskate.
Alot of the point of this thread is info seeking, "bench racing", basically fundamental discussion. I haven't turned a wrench on it yet.
Like rusty has said I have had 1 failure already. I know the reasons why, and no, I haven't told the whole story on what lead up to that failure.
But I DON'T want a 2nd. Call me gun shy, whatever. But I ain't the only person messing with these engines, and can't be the only one wondering "what if I do THIS" or what if I do "THAT" and I hope someone else out there is getting some good out of what's being discussed here. What's wrong with that.
Probably not unlike many, I want what I want out of it at the end of the day/ a long lasting torquey engine that doesn't burn oil, has more power than stock, gets the best mpg it can for what it is .. while I correct the factors that causes the first rebuild on this block to not work out. I don't want bragging rights for either cheapness or "get I spent the most of anyone on one of these".... I want bang for the buck, I know I have some leftovers from the years of working on cars and trucks, parts bought previously for projects that didn't happen for whatever reason, and wondering if I can put some of them to use to save a few bucks this time around.... If not then so be it ... But I'd rather ask someone who may have tried what I'm wonder about.... I'm sure somebody has.
Once I get the rough combo in place I know there will be tweaking and tuning.... I can deal with that.
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junkyardhero
Well-Known Member
no a flat cam can't be ground into a roller cam. you need like for like cores on them.
junkyardhero
Well-Known Member
i agree entirely. however, i think there are better choices than those 405's or some other such. like, stop trying to spin or re-use whatever you've got and make it work when that's just gonna require more work or wind up with some cobbled together end product that's all half-***.
buy the **** that's right for the build.
I figured as much but thought it wouldn't hurt to ask because just like that 1/2" socket that mysteriously disappeared until you return from the store to get another one then magically appears, I don't want to go but a bunch of parts and then have an "oh crap I could have used those instead " moment.
I can't believe what I'm having to spend between 2 of these trucks to piece together a couple of decent interiors for instance..... My 85 /6 truck and this 83 that I'm getting ready to build this motor for .... And I still need door panels/door "cards" for both. I have leads im following up on about an NV 4500 for this one, and a couple of more leads on a bell housing to mate the 4500 to this engine.... Still need a flywheel and the answers to the questions I've raised will have merit towards things like getting the right flywheel....
I can't believe what I'm having to spend between 2 of these trucks to piece together a couple of decent interiors for instance..... My 85 /6 truck and this 83 that I'm getting ready to build this motor for .... And I still need door panels/door "cards" for both. I have leads im following up on about an NV 4500 for this one, and a couple of more leads on a bell housing to mate the 4500 to this engine.... Still need a flywheel and the answers to the questions I've raised will have merit towards things like getting the right flywheel....
Besides guys it's bitin azz cold out there, I'm waiting for warmer weather, Uncle Sam to cough up my refund, as well as things like swap meets to start up again, what better to do than hang out here and figure some things out....
If you start looking at it as "how much I've spent" then it's no longer a hobby. A hobby is "I don't give a chit what I spend, I'm having FUN". That's why I never keep track....well, I do, but only loosely. If i keep track of every red cent, I'll end up playing Tiddly Winks.
Yeah I get that too. But I don't keep the checkbook in my pocket, and I do get the "what did you spend $95 on eBay for, now"? What did you get from Rock Auto this time? " What did you spend 13 hours on the road going to Iowa for "?
"What was in the box on the porch today "? All the time so I kinda gotta sorta at least keep track....
"What was in the box on the porch today "? All the time so I kinda gotta sorta at least keep track....
I'm lucky in that aspect. It's Kitty telling me all the time "get the thing, you never buy NEW car parts, because you're always fixing up junk"
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Like how my wife is bugging me to put the new trans i have here for the 01 Durango into it, even with its 314k miles on it already cuz she doesn't care for the 03 I replaced it with /that has a better body and so far still well under 1/2 of the miles of that 01....
That 01 Durango was the vehicle that the failed 360 was overhauled for in the first place.
That 01 Durango was the vehicle that the failed 360 was overhauled for in the first place.
Bobzilla
Well-Known Member
You CAN use the H405CP pistons you already have in a 5.9 Magnum block IF you get the rotating assembly balanced. There are also factory style replacement pistons available as part number H655CP and these have the factory style dish in them. If you compare the specs you will find you gain a little but of compression with the H405CP over the H655CP with everything else remaining the same. Is the goofy four valve relief piston crown on the H405CP the most efficient design? Nope. The dish in the H655CP is a copy of the factory Magnum piston and it's intention is to increase mixture motion on the compression stroke. You would probably use less fuel to make the same power with the H655CP (or a factory Magnum piston if you were not already over bored) than you will with the H405CP.
Use the compression calculators available on sites like Summit or Diamond racing to play with the numbers. But ultimately, you will have to decide if you want to run the pistons you have or buy new ones. Then, if you are ok spending the money on new ones, do you need more compression like KB107 or H116 or will the H655Cp work for you.
If it was me in this situation, I would sell the H405CP pistons and buy the H655CP for this truck engine. Then make sure you know what heads are going on it and what head gaskets you will be using and get the Magnum cam reground using the suggestion they give at Oregon Cams.
Sorry for the long post. Trying to be clear.
Long post alright, look at some of mine. What you're saying about buying the "right" pistons is probably what I'm gonna wind up doing. Those h655cp may be what's in there now, I know they have the factory dish like the originals did.
I didn't want to get into what caused me to pull this motor back out. But the first problem I had (and what made me decide to buy the doomed EQ heads) was while it was on the stand, the timing chain I put in had 3 crank keyways. I lined up the wrong marks and bent the valves on the original heads with a breaker bar... I tried to degree it in instead of just lining up and dots like I'd usually done in the past, got some really weird results and confused the hell out of myself, and being that I'd only ever degreed one timing set in prior, which had been years prior, I figured that the oddball results were just my lack of having used a degree wheel in so many years decided to say "screw it" and went with it.
I didn't want to get into what caused me to pull this motor back out. But the first problem I had (and what made me decide to buy the doomed EQ heads) was while it was on the stand, the timing chain I put in had 3 crank keyways. I lined up the wrong marks and bent the valves on the original heads with a breaker bar... I tried to degree it in instead of just lining up and dots like I'd usually done in the past, got some really weird results and confused the hell out of myself, and being that I'd only ever degreed one timing set in prior, which had been years prior, I figured that the oddball results were just my lack of having used a degree wheel in so many years decided to say "screw it" and went with it.
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Ahhh... Fark ... You guys are dragging the story of the failed rebuild out of me .. but that was only one of 3 things that happened while putting this thing together. And embarrassing at that.
After I pulled the heads and replaced them with the EQs I discovered my first mistake. I corrected that before I made the same mistake again.
Then once I got it in and running it sounded great at first. But as it warmed up it started running like crap. I shut it down, let it cool, and started it again the next day, would barely start, wouldn't idle without keeping my foot on it, and decided to try to take it for a short ride in the country and made it about 3 miles, it stalled, I had to call the kid with his truck and a tow strap to get me back home that 3 miles, parked it and left it sit about 3 years.
While I was sitting waiting for him I noticed that my brand new cat was glowing bright red. Melted, and the reason I couldn't even get it to run again. This truck the motor is going into now, ain't gettin' a cat.
After I pulled the heads and replaced them with the EQs I discovered my first mistake. I corrected that before I made the same mistake again.
Then once I got it in and running it sounded great at first. But as it warmed up it started running like crap. I shut it down, let it cool, and started it again the next day, would barely start, wouldn't idle without keeping my foot on it, and decided to try to take it for a short ride in the country and made it about 3 miles, it stalled, I had to call the kid with his truck and a tow strap to get me back home that 3 miles, parked it and left it sit about 3 years.
While I was sitting waiting for him I noticed that my brand new cat was glowing bright red. Melted, and the reason I couldn't even get it to run again. This truck the motor is going into now, ain't gettin' a cat.
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At least 2 injectors of which I had sent off to be rebuilt along with the engine rebuild, stuck wide open I'd discovered and washed it out like a stuck float can. I gotta get ready and head to work, can't hunt and peck no more right now. I'd told about the stuck valves in those brand new heads much earlier in this post. But I'm wanting to toss the pistons that I have in there now because they've already taken a beating.
The last straw when I decided this motor was done at the time, was getting it home and drained the oil, and got a silver slurry out of it that I have never seen before.probably because of the stuck injectors.
That was towards the end of 2016, it would be 2019 before I touched it again, found a used one on CL to get the Durango mobile again. I put that motor on the stand to re gasket it before I put it in, found out those heads were cracked, so I pulled my new EQs off the doomed rebuild and that's when I discovered the bent exhaust valve on #4. So I had to send them off to the machine shop, and the doomed short block has been on a stand ever since.
And the machine shop said they'd seen engines that were dragged out of a field after 30 years that they didn't have to work so hard beating the valves out of compared to this set ... Remember. Ready to run right out of the box"...
That was towards the end of 2016, it would be 2019 before I touched it again, found a used one on CL to get the Durango mobile again. I put that motor on the stand to re gasket it before I put it in, found out those heads were cracked, so I pulled my new EQs off the doomed rebuild and that's when I discovered the bent exhaust valve on #4. So I had to send them off to the machine shop, and the doomed short block has been on a stand ever since.
And the machine shop said they'd seen engines that were dragged out of a field after 30 years that they didn't have to work so hard beating the valves out of compared to this set ... Remember. Ready to run right out of the box"...
C'mon guys you've wanted the story behind this engine, there it is. Please don't bail on me now
The rebuilt engine was also originally a CL buy, that I got conflicted stories about. The most believable one was that they'd bought it from a junk yard and bought the wrong one for their application and were trying to get their money back, as the junkyard wouldn't. I pulled it apart because of those conflicting stories I definitely appreciate the feedback I've gotten so far.
The rebuilt engine was also originally a CL buy, that I got conflicted stories about. The most believable one was that they'd bought it from a junk yard and bought the wrong one for their application and were trying to get their money back, as the junkyard wouldn't. I pulled it apart because of those conflicting stories I definitely appreciate the feedback I've gotten so far.
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