944 connecting rods & crank problem

xupkid2 · 11-14-2006, 08:45 AM

I am in the process of rebuilding my 1988 944 NA motor. I had the crank crossdrilled and balanced and installed new main and rod bearings. The problem I am having is when I tighten down the connecting rods to the proper torque they are seizing up on the crank, the main is fine. This only happens on the #2,3 & 4 journals. I checked the oil clearance of the bearings with plastigauge and the clearance is well within the specs. I am now assuming it is the sides of the rods that are hitting the sides of the crank journals but Im not sure.

Anyone else ever have this problem or does anyone have any recommended solutions?

ae1969 · 11-14-2006, 10:05 AM

UHmmm you did not reverse the rod caps did you? they only go one way.....

ae1969 · 11-14-2006, 11:11 AM

.... the numbers stamped on the rod and cap should be on the drivers side...

JivenJim · 11-14-2006, 11:50 AM

I had a bent Crank that gave me the same Problem. Did your shop Check for that? First time I did this I also had the Caps Reversed and not matching numbers like AE says. Clarks says if crank binds, loosen it all up and redo.

AFJuvat · 11-14-2006, 01:07 PM

Also, did they break the edges of the oil holes and micropolish the crank?

AFJ

xupkid2 · 11-14-2006, 01:40 PM

I know for a fact that I did mount the connecting rod ends on the wrong way. Its a shame it took me till having the motor back in the car to find that out. Looks like its going to take a bottom end tear apart from the underside to fix the problem. As far as the crank goes, Lindsey Racing did the work so I assume it was done the correct way.

hpaulb · 11-15-2006, 06:17 AM

Did the same with my first engine rebuild as a teenager. Was in a hurry as it was my only transportation. Mixed the connecting rod caps. Engine lasted a couple days before it siezed on the street.

Zero10 · 11-15-2006, 08:45 AM

Wait, the crank was siezed in place, and you INSTALLED the motor?
I need to take a step back.......

When I built my motor, I mis-matched the rod caps. It is strange, but both tangs go on one side (although still on opposite sides if you get my drift). This is what really threw me. The key is to match the numbers up. If they are on opposite sides, I guarantee that the rods will bind on the crank even though you have the appropriate clearance.

xupkid2 · 11-15-2006, 09:19 AM

That is the exact problem I have. I tightened the rods down and the crank still turned but it was hard to turn. I figured it was how it should be so I installed the rest of the motor and got it to run for about 15 min. then I shut it down and now it wont turn over. I realized now cause of the posts on the site that I put the caps on the wrong way which is why I am having the problem. My hope is that I didnt mess up anything badly and that I can pull the bottom end apart and flip the caps and be ok but Im doubtful that will happen.

ae1969 · 11-15-2006, 09:29 AM

OUCH... thats painfull...

Well... the bearings probably spun........ how much got scored is the big question.

hpaulb · 11-15-2006, 10:56 AM

Well I would say the bearing most likely heated to the point it melted to the crank. Usually this problem requires the crank to be machined one size over. Regular engines = 10 thou. Porsche may be 25thou. Look for bearings on this site and you'll find size. Easiest is a used crank and another set of con rod bearings. What happens is that on manufacturing, the con rod's are line bored. Caps one and bored to a specific circumference. Cap is now is mated to conrod only.

Sorry

Razorback1980 · Razorback1980's Garage

You really hate it when something bad like that happens, but don't feel too bad, I think we have all done similar things at one point or another. If I wrote about all the stupid things I have done, this would be a really long post. If you haven't done something wrong, then that's because you haven't done anything.

If you do need a new crank or any other parts, let me know and I'll see what I can track down for you.

xupkid2 · 11-15-2006, 03:10 PM

Tom

Thanks for the boost. Im really hoping I didnt screw things up to badly since it didnt run very long and was just at idle. The good thing is that it didnt seize while it was running and only did when it cooled down. I may also still be able to break it loose if i drop the starter because my starter isnt almost shot so it might still be ok. With my luck though its probably a bigger problem then I would ever want. The worst is that the crank was brand new and I just had it machined by Lindsey Racing so this may be a very expensive mistake. I guess we'll see over Thanksgiving when I tear the bottom end apart.

JivenJim · 11-15-2006, 03:26 PM

Personally, I would not hit the panic button yet. When you pull the bottom, Check the end Caps for rounding (from grinding on Crank).
And if the your oil pan doesn't look like your panning for gold; You might just be OK. Change the Conn Bearings and you're back in business.

Hope floats...

Granite 944 · 04:56 PM

IF, your machine shop did all the machining that they normally would do, than line boring should have been part of it. Thusly, the caps must be installed in their proper placement/configuration. (note the FSM and standard rebuild practices). IF you don't have the FSM, you are in trouble if your assembling an engine without it. Read it, re-read it, know what you need to do, before you start. NO SHORTCUTS, or....... "I'm in a hurry here"... will make it. Ask questions here along the way, if even slightly unsure of yourself, BEFORE you proceed to the next step.

Plasti-gauge technique just didn't pic up on the wrong installation process here. Side mismatch COULD very well be a problem here.

Teardown is indeed in order, and revisiting all aspects of checking the crank and the bearings IS of the most importance, subject to following the above processes to the utmost here.

You may or may not, have destroyed the crank. You feel lucky?

You really won't know for a while. Good luck!!

Edit: you say it "seized up". To me, that means, you can not turn the engine over by hand, using a socket on the crankshaft bolt, with the plugs out, and a two foot breaker bar or equivilant..........cold, or hot. IS this the case? DON"T make more work for yourself, if this isn't the case. Answer this.

Aerkuld · Aerkuld's Garage

Quote:

Originally posted by Granite 944
IF, your machine shop did all the machining that they normally would do, than line boring should have been part of it. Thusly, the caps must be installed in their proper placement/configuration.

Line boring applies to the mains and he is talking about the big end bearings on the connecting rods if I read it correctly.

You're right about the rest though. If in doubt read, check, re-read check, and check again. Only continue once you are absolutely certain.

Don't worry xupkid2, everyone makes mistakes, and as long as no one gets hurt, you learn from them, and don't do it again you're better off from the experience.

Razorback1980 · Razorback1980's Garage

I agree...pull the plugs and see if you can turn it by hand on the bolt in the end of the crank. Don't do it too much though but it's an indication of just how bad things are. Of course you won't know for sure until you pull the pan. Good luck..let us know how we can help you.

xupkid2 · 11-20-2006, 08:57 AM

When I say the engine seized I mean that I try and turn the engine over and the starter does not turn the crank. It just burns up the starter. I have not yet removed the starter and tried to turn it with a socket and breaker bar yet.

This past weekend I drained the oil and did not find metal particles in the oil which I am hoping is a good sign. This weekend will be the test when I pull the pan.

Usmellgass2? · 04:40 PM

Sorry to hear about your misfortune. mistakes are easy to make. I got plenty of my own story's

Let us know what you find during tear down. I would expect you will need a set of rod bearings at least, hope the crank is OK and there is no debris in the oil. Cut your filter and look there too. You should always dissect your filters. Contact Lindsay, they will walk you through this and make shur its done right. They are good guys and will be on your side as long as you are reasonable and dont BS them. Have the rods been reconditioned? Plastigage will only tell a small part of the story. A inside mike or snap gage and o mike will help tell you if all is round and true. Be very careful to note / photo all positions, orientation, wear/ damage ect. Many of us here on the board will be happy to help you out. Feel free to call me if you want, PM for my number.

GL
Dave