ok I have an 84 Ford F250 with a built 351 windsor. I rebuilt the whole motor top to bottom and broke it in nice. I put about 1500miles on it and then for some reason something started having a little knock. I pulled the pan and one of the rod bearings has some clearence.

My question is, when i replace this bearing. If I run the motor in at 2000 for 15 min, then im done. No thousand mile ventures to break it in. I would imagine that it being a surface for the rod to ride on it has no give. So that wouldnt make much sense to run it for so long before I can be mean to it.

Let me know what you think. Also since the rings and pistons are all sat in already. Can I use synthetic oil first thing? I kno usually you use a mineral type oil but everything else is already seated.

 

You should be able to just replace the bearing, get the engine up to operating temperature and be perfectly fine. I don't see why you couldn't go right ahead with the synthetic oil either, as long as the rings are seated and the cam is broken in already as you said.

 

Its got 1500 miles on it so its pretty safe to say its broken in. ok thank you much!

one last question for you since it seems like your knowledgeable. On my oil pump you know how theres the bypass spring inside the pump housing. Can I tap the metal plug in a little LITTLE bit to raise the pressure relief? like say 65 to 70 or 75 lbs.

You might ask why I need that much but this motor is FAR from stock trim not to mention it sees high rpm usage. thanks

 

No, you can't.

 

Why does that bearing have clearance, exactly? I don't think just replacing it is going to solve your problem.

 

You said you had some clearance. Why? Did you mic crankshaft or plasti-guage the bearing before final assembly? Rod and cap checked for roundness? No need to put in new bearing til you find out the problem. If shaft is worn and still smooth and in good shape, sometimes bearings can be found in .001 and .002 undersize.

 

I havent the slightest what happened. I loaned my truck to my brother and it came back knocking. So i dont think it takes rocket science to figure out what he was doing.

I mic'd and plastied every cap and bearing. All were tight. I had everything resized and I got all the right bearings for it. It ran for 1500 miles then it started to knock a bit and my oil pressure was lower than normal.

 

Make sure you do it again. What did the bearing look like and did the rod bolts seem too be torque range tight when you loosened them? I think we all know that your brother would NEVER THINK of abusing your truck, ... No, what I meant to say is he would NEVER THINK. You never know though, coulda happened to you anyway. Are those re-used stock rod bolts? Hate to see you put this back together without a solution to the mystery, or you could have a rod through the pan in the next 1500.

 

I re-used the stock rods and bolts. The machinist said they were in good shape still. The bolts didnt take a lot of effort to break em loose. yea hes a little more abusive then myself.

I put it back togethor tonight. I am rather angry and I have a mystery. ok So i still have my "knock" and low oil pressure.

It runs 65lbs cold pegs it. Fully hot 10lbs at idle. JUST like before. I cannot figure it out. When you rev it, it goes up just not very fast. This is also a HV pump.

I replaced the pump and pickup just for insurance and I replaced EVERY main and rod bearing. THE HECK! HELP ME!

 

Sounds like too much bearing clearance. Did you check bearing clearance with a dial bore gage when it was being assembled.

 

You didn't say what the bearing surface looked like so I'm going to assume it was in good shape. The only thing I can think of is that rod has to be out of round. Loose cam bearings and a bad wrist pin could concievably cause a similar symptom, but that would mean 2 things going out at once and you said you found some clearance in that rod, so that's where I would look first. By the way, what are the clearances we're talking about here? Personally, I would change out at LEAST the rod bolts on the suspect rod.

 

Gearhead, did you re-check the clearances before the PBT? I did not read here that you did anything to check them. That will give an indication of the general condition. You have to check them all, and a visual inspection won't be enough. If you have one bearing with excessive clearance, you will not get good pressure hot. You can mic the rod journals at 90 degrees to check for egg shape, but it's hard to check the rod big end diameter for roundness in the engine. The mains are also difficult. You could do a plastigage extravaganza, checking them all in one position, writing down the clearance, then rotate 90 and check them all again. That would give a good idea if the journals are round. Lots of assembly / disassembly. Might be easier to pull it. Maybe get some help from your sibling. Maybe get a new sibling.
tom