360 magnum. 1 piston lower in cylinder??

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JoePole1

JoePole1

A dude in a B body
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So I purchased a low mileage (70k) 360 magnum and pulled the heads to install a set of EQ's and noticed that 1 piston is down in the hole a lot more than the other 7 at TDC. I don't have the proper micrometer to measure deck height but a rough measure is about .17 as compared to the others that are approximately .05 inch. This engine has never been apart since it left the factory and the markings are the same on all pistons. The cylinders look great with cross hatching visible and the same amount of slight carbon build-up. Any idea what this flaw is and how to remedy? Do I even need to be concerned?
This is going to be a budget street engine built for reliability with about 375 hp and 400 tq.
Would rather not have to replace the pistons or crank.
 
JoePole1 said:
So I purchased a low mileage (70k) 360 magnum and pulled the heads to install a set of EQ's and noticed that 1 piston is down in the hole a lot more than the other 7 at TDC. I don't have the proper micrometer to measure deck height but a rough measure is about .17 as compared to the others that are approximately .05 inch. This engine has never been apart since it left the factory and the markings are the same on all pistons. The cylinders look great with cross hatching visible and the same amount of slight carbon build-up. Any idea what this flaw is and how to remedy? Do I even need to be concerned?
This is going to be a budget street engine built for reliability with about 375 hp and 400 tq.
Would rather not have to replace the pistons or crank.[/QUOTE
I would first turn crankshaft forward and back and determine how far it moves before piston does.
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Gonna have to put another pan and oil pickup on it anyway, and I would sooo at least check that rod bearing.
70k is almost nothing for a Magnum motor, so it should look like it's almost new down there.
 
Thanks Trail. That is the plan. I have new rod and main bearings set to go in and I agree that it's unlikely the engine has wear. I think it's a factory flaw. But what??? I am switching to LA cam cover and don't want to purchase any more parts if this is going to start snowballing into a money pit. I can just swap the EQs and cam up my current LA 360.
 
JoePole1 said:
Thanks Trail. That is the plan. I have new rod and main bearings set to go in and I agree that it's unlikely the engine has wear. I think it's a factory flaw. But what??? I am switching to LA cam cover and don't want to purchase any more parts if this is going to start snowballing into a money pit. I can just swap the EQs and cam up my current LA 360.
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Cool, and for sure check that rod like mentioned.
Don't know why I missed that.
 
Glad you caught that! You gotta fix that for sure.. compression ratio will be down by more than 1.5 points in that cylinder.... assuming it is not a bent or damaged rod. It would run like a 3-legged dog LOL

For the rod to NOT be bent, the piston's compression height would have to be around 1.50" and I don't know of one like that; way too short for any standard pistons, and too tall for a 4" stroker piston. So rod damage seems likely.

Look for any evidence of water/coolant in that cylinder. And, if the rod is bent, I would take out the crank to check for straightness and 90 degree indexing of the journals; that rod AND crank journal saw some force.

Not really much choice but to fix that damage/problem. If it is just one piston & rod, then that is not much work; you can borrow a ring compressor from some of the auto box stores.
 
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Check the head on that side, if it’s cracked into the water jacket then that would explain a bent rod, hydrolocked!!
 
Thank you All!!!!! I pulled all 8 pistons from the block. Sure enough the # 8 rod is bent. Amazingly all cylinder walls and the skirts on #8 look good. Some wear on that bearing but not much more than the others. Fingernail test was even good. I'll plasti-gauge the crank and replace all bearings along with the bad rod. As far as the old heads go, they look Ok but I'm putting on EQs on anyway. Looks like I got lucky here. Thanks again.
 
One more question. The piston pins are pressed on. Is this something that can be done at home or is that a job for a machine shop?. I think I can get access to a press. Any tricks?
 
Good call on post #5! If you're not having the crank checked, then at least put it all back in, and find where #1 is at TDC. Then turn the crank with a degree wheel and see if #8 is at TDC EXACTLY 90 degrees later. That is a backup check on the crank for indexing. It won't necessarily find bends in the crank.

Pressing out the pin without damage to the piston has erratic results, regardless, so be ready for a new piston. I don't know any local shops who will guarantee no damage. So, if you ask and they won't, you might as well try yourself. Putting the pin in without heating the rod end can do the same. Freezing the pin might help some.... but I never bothered trying that; they just go to the local shop.

Can you perhaps find a stock piston-on-rod assembly on eBay?
 
Thanks. Checking ebay now. Do LA 360 rods interchange with Magnums?
BTW....Was down in Waynesboro a few months back. Nice country down there.
 
Glad you liked it.... you shoulda stopped by Eastside Machine shop.... a very good shop that, on the outside, looks like it was closed years ago LOL... but they do some good work there.

The small end of the Magnum rods are narrower IIRC so the LA rod does not fit in a Magnum piston as far as I know. And I think the Magnum rod is lighter too. So I'd not try that.
 
Yeah, the balance factor is considerably different from la to magnum rods.
 
JoePole1 said:
One more question. The piston pins are pressed on. Is this something that can be done at home or is that a job for a machine shop?. I think I can get access to a press. Any tricks?
Click to expand...
It can be done. just find a quality machine shop.
 
Thanks. Will ask around. I have a machine shop fairly close by that Mopar Action mag refers to quite often. If so I'll get the crank checked first and maybe balance. Spoke with the guy I bought the engine from and he feels bad but swears the engine ran strong when he bought it. Looking at the condition, i kinda believe him. He never installed it into his Ram because the frame was rusted out. Hate to give up on this core. Already purchased new bearings, gaskets, pan and pick up so I have about $500 into my $2k budget.
 
That nice 'top fueler rumble' that it had is now explained LOL. No reason to give up on it that has yet shown up. Just check for the thing mentioned so far.

No need for a crank balance if the crank is not bent and it you are putting in the same pistons and rods, and bearings and ring types. That that would cost beaucoup bucks for no good reason.
 
JoePole1 said:
Spoke with the guy I bought the engine from and he feels bad but swears the engine ran strong when he bought it.
Click to expand...

I bet it would show up on a scan tool. My Solus shows misfire data, even though it doesn't feel like a miss or skip. You probably wouldn't have noticed.
 
I was thinking of loss compression but also will be made up for that by the extra volume? A bit of a low compression stroker in that cylinder?
 
Thanks all. appreciate your input.
I will have the crank checked out and have a close look at #7 rod as well. Let's say crank is garbage and I decide to blow the budget....
Can I install a stock bore stroker kit with a DIY cylinder hone and NO further machine work? Remember..I already have EQ 1.88/1.62 heads with decent Comp springs.Also have the Mr Gasket thin head gaskets.
 
Sure..... ring seal may, or may not, be great though. Stroker pistons are vertically short, and tend to need to be snugly clearanced to the bores, in order to not rock a lot. If they rock a lot, then the ring seal gets worse/bad/poor. If this idea comes to pass, then I'd suggest measuring the bores carefully and accurately first, and then present the data for further discussion.

BTW, if you had another rod, then you might be able to save some $$ by buying the stroker crank and pistons, and having them balanced locally. Depending on how hard you intend to push this, a cast stroker crank may be just fine. Just a thought....

One other thing, with the displacement of the stroker, the shorter Magnum block, and those small chambered heads and thin head gaskets, you need to compute the static compression ratio (SCR), and then at the cam you want for your intended use, and then examine dynamic compression ratio (DCR). If a smaller cam is appropriate (for street cruising for example), then the DCR could end up too high and the engine would be prone to detonation. Those matters can all be helped with on this forum. It can all be fixed, but you need to know where this will end up before blowing the $$.

BTW, what is your intended use for this engine? OK, I see... street engine..... but 'Street' means different thing to different people. Is this more for cruising, or some drag racing, straight lines only, or spirited driving around curves, or what? (You have a lot of older curvey roads in your area, so I might guess something akin to road racing, but that is too much of an assumption to make on my part.) Gears? Trans type? Car model? etc.
 
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