I've been trying for weeks now to get my pistons in my new engine and keep hitting problems. Here's my latest and so far most confusing one. When I put my pistons in, I put four in at once and tried turning the engine over by hand. It took a lot of force to turn it over, but it went. Then I put the next two in and it was impossible to turn. I mean I put 100 ft./lbs. on it and it's didn't budge so I stopped. I took all the pistons back out and started over again. I put the first one in in the back and the engine turned no problem. Then I put the second one in in the back and it still turned with no problem. Next a took a suggesiton from a neighbor of mine who's a mechanic and put the next piston into the front of the block. When I first installed it, the crank turned fairly easilly, but I tried it again like half hour later and it won't make a full revolution now. What's with this!!??

 

I had this happen when i was building a 350 sbc truck eng. Come to find out that 4 piston were installed wrong on the rods and the binding was at the crankshaft. When i installed the pistons i looked at the top of the piston for the mark that should point the piston towards the front. Brought them back and the mech. turned them around and all went well.

-Auggie-

 

Auggie,
Thanks for the tip, but I already checked to make sure the pistons were on the correct rods. I don't understand how the assembly would rotate and then half hour later bind up to the point that it won't make a full turn?

 

Paul,

How tight are the rod cap bearings? If you keep the rod cap bolts just snug instead of torquing them to spec, does it help? If your bearings are a little on the tight side, and the rods, caps, and bearings are warm from handling, they will be slightly larger than the cold crankshaft. Once the temperatures equalize, the sizes will change slightly.

Are you wetting the assembly as you assemble it? Some assembly lubes are fairly viscous and sticky so that they cling for long periods. Any combination of these factors could cause your symptoms.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

ok maybe a stupid question, but are your bearings the correct size? rod bolts not hitting the cam or oil pan rail? as stated before the rods facing the correct way? have someone else check it so you are missing something you missed to start with.

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-=ICON MOTORSPORTS=-

 

I already had a mechanic look at it and he told me to just add the pistons one by one and as soon as I put one in and it didn't turn, then that was my problem child. The only thing is that when I put the two back ones in they turned no problem. Then it turned no problem at first with the front one installed also, but then after a short time it tightened up? I don't get it.
Vader.....is there any logical explanation for this? Did the two back pistons somehow bind up?

 

Here's just another random thought that I just dreamed up. Since the pistons were in the shop twice to have the skirts shaved and the rings were removed each time, is it possible that bent rings could cause this problem??

 

Maybe i didn't explain what i ment very well. Anyhow, before you install a piston & rod look at the rod big end. One side of the rod big end is flat and the other side has a large chamfer. When you install two rods on one journel the chamfered sides should go to the outside of the rod journel and the flat sides should be next to each other and have around .010" to .015" clearance. You can check this clearance with a go-no-go feeler gauge. What was done to the pistons?????

-Auggie-

 

I already checked the rod configurement and it's correct, however there is next to no room at all inbetween them. I don't see how this is really possible, but that's how it is. My mechanic friend said that the two I had together on the same journal were fine. It only took like 7-10 ft/lbs to turn it over. Anyone have any thoughts on my bent rings theory?

 

have you checked you piston to wall clearances? after reading that you've had the skirts worked on i think i'd be checking that if you haven't already. also have you checked the ring end gap?

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-=ICON MOTORSPORTS=-
1st & 3rd

 

Your two top rings won't bend, they break. The oil rings could bend but if that were the problem the crank would have been hard to turn as soon as you put the piston in, and 30 minutes later.
Like Vader said, a lot of assembly lube will make the crank "stick" to the bearings and it will take a fair amount of force to break it free and then it should turn easier again.

 

Did you check the bearing clearances? I like .00225" - .00275" on the rods. From what your describing, it sounds like somethings tight there.

Here's a couple other flags going off in my mind.

Are you using an aftermarket crank or ground crank with a large fillet radii at the corners between the journals and crank cheeks? If so, you need to use champhered bearings or champer the ones you have.

You said that you have almost no room between the rod ends. You should have between .015" - .025".

As already posted, the top and second ring wont bend. They'll break before that happens.

I'm asuming your using a good assembly lube on the bearings and piston skirts.

Mike

 

Well I'm using an aftermarket 9000 SDPC Scat crankshaft. I don't really know if this could happen, but is it possible that the journals aren't the correct size? Also what was meant by using chamfered bearings? Would this help me? How could I check this? What I mean by bending piston rings wasn't bending out of round, but bending into what would form a vertical spiral if you were to connect a number of bent ones.

 

Well Paul you really got us going on this one. OK, you said that there is little or no con rod side clearance. This has to be fixed. My SM say's that rod side clear. should be between .008" and .014"! If you don't have any side clear. the oil will have a hard time leaving the con rod bearing journal which will cause overheating and bearing failure. When i assemble a short block i shoot for a 20 to 25# torque reading for the entire rotating assembly.
I also ran into a problem like yours on another occasion. The problem was the three piece oil ring. The oil ring spacer should not be allowed to overlap in the ring grove. Make sure that the oil ring spacer ends butt up to each other before you install the two oil rings. Some oil ring spacers have an anti-rotation tang and that has to fit into a drilled hole in the oil ring piston grove. Don't give up, you will find the problem!

-Auggie-

 

I think it's because he's putting the rods on the crank the wrong way. Like a previous poster described, the flat side of the big rod ends "butt up" to each other on the crank journal and the little "lips" that they have on the outside go towards the counterweights. I had this SAME problem with mine. I say I'm sure about this because you said you have no clearance between the rods. THIS will do that. It happened to me... (yes I'm an idiot). LOL Anyway excuse the trailer park lanuguage, but I used it to make thigs easier to understand. Hehe

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

Paul,

It's crucial to ALWAYS check bearing clearances. The best way is with a bore gauge that reads 10 thousands. You use an outside mic on the journal, lock it down, then put it in a mic vise (or anything to hold it). Then you set the bore gauge to zero with the mic. Once the bore gauge is zeroed, you check bearing ID with it. The gauge will give you the difference between the journal OD and the ID of the bearing. The rod (or main) caps need to be installed with the bearing and torqued to spec prior to checking their ID.

If you don't have access to a bore gauge and mics, then plasti-gauge should be used at an absolute minimum.

Many aftermarket cranks are ground with a large fillet radii at the ends of the journal (right next to the crank cheeks) for added strength. All forged cranks are ground this way. When I have a crank ground, I have it ground this done as well. I'm not familiar with your particular crank, but I'd bet it requires chamfered bearings. I'd call Scat and make sure anyway. You can also tell by looking at the crank. A stock cast crank will not have any noticeable fillet at the crank cheeks (it will be flat all the way across the journal up to the crank cheek), the others will be very noticeable. The chamfered bearings have a chamfer (bevel) cut into them on the side that faces the crank cheek. This chamfer is needed or the bearings will bind up on the journal (which will be very noticeable when you put the second rod on the journal).

Paul, you would have to be trying very hard to bend those rings and would need to heat them with a torch as your trying. They are made of a "spring steel" alloy. They have a memory and will return to their original shape or break. It doesn't matter which way you try to bend them.

You can bend the oil control ring/rings. I doubt that's your problem though.

BTW-Don't be supprised if it takes around 50-60 pounds on a torque wrench to role an engine over with all the pistons/rings in it. I seat my rings dry, and have had up to 80# if I build it real tight with standard tention oil rings. After roling it a couple dozen times, it will loosen up.

Mike

[This message has been edited by md (edited November 06, 2000).]

 

Well I know for sure that the rods are being installed in the correct direction, so we can discount that idea. I'm going to look into whether or not I need chamfered bearings and if so why the manufacturer didn't state that on the paper work that came with the crank. Until then I'm still open to any other ideas. Thanks for all the help guys.

 

Your problem sounds like the classic rods-on-the-pistons-backwards situation.

Look at the pistons; are the notches (or other marks) oriented toward the front? If so, then look at the big end of the rods. Are the bearing tangs toward the outside of the assembly, away from the cam? If the rod is turned such that the bearing tangs are closer to the cam, here's what will happen: many bearings (notably F-M high-perf ones) are made as wide as they can possibly be. When they do that, the bearings are no longer symmetrical. (They still are the same top and bottom though.) The edge of the bearing that is made to go on the side of the rod that adjoins the other rod is wider than the side that is that is intended to go next to the crank throw, and that is therefore chamfered. If the rod is backwards, then the flat un-chamfered side ends up on top of the radius of the crank journal. Since you mention that there is no space between the rods, the symptoms scream that this is your problem.

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"So many Mustangs, so little time..."

 

I've already checked that problem numerous times. The oil spurt holes are towards the cam, not the bearing tangs. Also the dots on the pistons are facing the front. They are definately in the right way.

 

Hmmm....

So exactly what interferes? Here's some things to look for:

1. When you put 2 rods on the same journal (#1 & #2, or #3 & #4, etc.) will each of the rods slide freely from side to side on the crank, with about .015" of free unrestricted clearance?

2. Is the side of the small end of either rod smashed up against the pin bores? That is, can you see pin between both sides of the small end and the piston?

3. If you look at the bearings after you've spun the engine over with 2 of them on a journal, can you see any sign of wear on the very edge of the bearing?

4. What are you using for assembly lube? My personal preference is either 0W-30 Mobil1, or ATF. Thinner is better IMHO.

There's definitely something not put together right somewhere. The only other possibility is that the block has enough core shift that the cylinders are too far to the front or the rear of the crank journals, which might have worked if the space in the piston for the small end was larger with the old pistons than with the ones you are using now. I've seen that happen before.

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"So many Mustangs, so little time..."

 

Well I'm using 10-30 Mobil 1 in the cylinders and ARP supplied assembly lube on the bearings and bolts. I'll have to double check on the piston pins when I go home again for Thanksgiving. What would wear on the bearings look like? I tried to get in touch with SDPC to find out if I need chamfered bearings, but their customer service is really poor. I've tried many times to contact them about other problems, but they are really slow.

 

ARP lube for the bearings? I hope it's not their thread moly your using.

RB,

You use ATF on the bearing journals for assembly? Can't say that I'd agree with that practice but I've been wrong before. ATF is good for cleaning, but assembly.....???

I like to use Synergin or Redline assembly lube. It'll stay put until the enging is ready to fire. I'll use it on the skirts and a little in the ring grooves but I keep the cylinders dry.

 

You would see bright copper, along just the very edge opposite the chamfer. You might need a magnifier to see it well although they should be the dull tin finish all the way across and around the edge, so if there's anything shiny there, it would be the wear in question.

If it turns out to be that, the bearings aren't too damaged to use once you rectify whatever the underlying problem is.

My experience with turning motors as I assemble them (and my radius preference!) agrees with md's, although I would guess slightly lower than he does. The main point would be that it should turn freely, with each added piston & rod adding equally to the total torque required.

You might want to do all your troubleshooting assembly without the rings, to save some time and the wear on them.

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"So many Mustangs, so little time..."

 

Uh-oh!! I've been using the lubricant that came with my ARP fastners to lube the bearings. I realized just now that this is a BAD thing, but I don't think it would cause my binding problems. I'm really stuck on this one. I'm really running out of ideas and people to ask here.

 

Okay Paul, I’ve asked you twice and I’ll ask you one more time. Did you check the clearances? Bearing journal and rod side to crank? What were they? We can’t rule this out as a problem unless you tell us if they’re within spec. Okay?

Also, we need to know if your crank requires chamfered bearings. If it does and you are not using them, I guarantee that the crank/rods will bind.

The ARP molly for fasteners has particulate matter in the base (long description that I wont get into now). It will effect how easily the rotating assembly turns. It will also damage the bearings if you rotate the assembly too many times. I doubt that has happened, but don’t use it anymore.

Re-read your ALL the questions asked in your string and answer them please so we can stop chasing ghosts and look for other possibilities.

Your getting a lot of help here, but we MUST KNOW what your findings are before we can look at other possibilities.

These replies take time and effort. We need a little feed back from you. HELP US HELP YOU!

 

Ok here's what I now know. I haven't measured my journal and bearing clearances because I really don't know how. I would do it if someone told me, but I won't be home until Thanksgiving now, so I can't give you any answers on that. I posted a question about bearings with my crank on the Scoggin Dickey message board here and another member said that he thought the crank needed chamferred bearings, but I'm still waiting to get a definate from SDPC. Hopefully this is my problem. If so I will be sure to use the correct assembly lube on my new bearings. I'll let you know how it turns out.

 

It's official!! I called SDPC today and they told me I need chamfered bearings. Nice of them to tell me that in the first place!!! Thank you to everyone who has helped with this lunacy of a witch hunt.