Ok, I did a search but couldn't find a solid answer to this. Is it possible to replace just the crank and main/rod bearings and have the engine last for another 30k miles? The motor (302 Ford) has good compression and doesn't smoke but the oil pressure gauge jumps from 40 psi to zero under load when the engine has warmed up. When it's cold or at idle it reads fine, so I'm guessing it's the bearings going bad. the top end is relatively new so I'd prefer not to rebuild the whole thing yet if I don't have to. SO, can I just put in a crank kit and get it to work a while longer or am I up crap creek? Thanks
You ask if it's POSSIBLE.....yes, it's possible; it's also possible that the crankshaft to bearing clearance isn't your problem. Are you a gambling man?
I'd replace the oil pump and pickup as well on general principle, just don't want to have to take the whole thing apart if I can just swap the crank and bearings. Not looking to make it bulletproof, just last another year or two of normal driving. So, does anyone have experience with this?
call me simple but i like to get another gauge and back up eratic readings. then go with heathen and flat mountain
If the guage checks out Ok and the wear is in the bearings, you can pull the engine, turn it upside down on an engine stand and replace the crank and/or bearings. No need to pull the heads or pistons. Not as much fun as a bare block, but not THAT bad either. You COULD just try replacing the oil pump and see what happens, or while you've got the pan down for that, pull a main and a rod or two and see what they look like and/or plastigage them to find what clearances are. If the results of that isn't encouraging, pull the engine, you haven't lost much time, but could have saved a bunch. Ray
Fix it right once or half-ass over and over. I know sometimes the budget forces the latter but right always ends up less expensive.
Normally, I would agree wholeheartedly.......but he said the top was relatively fresh........that would have been the time to do it all and the current situation proves your point........but, he is beyond the opportunity to "do it right the first time". Ray
I've seen several small block Fords in my time with clogged oil pump screens do exactly that. They carry oil pressure until the revs go up then it falls off. We (shop where I worked) changed the pump and pick up screen and they went down the road.
I did it once a long time ago to a sbc while still in the car. It was a pain in the ass but it worked out well. I just can't remember anymore why I needed to do it?
I would change the oil pump and oil first.On most overhead cam engines oil pressure is measured at the cam bearings,so if you redone the topend ,did that include cam bearings ?Go oil pump with a motor flush/oil change first.................YG
Hey flat_mountain How many total miles does the engine have on it ?? Was the timing chain replaced when the top end was freshened up ?? What year and model is the vehicle ?? You might pull the pan and see if the screen is pulling debris into it after running a bit and clogging it up. I have seen that quite often, sometimes gunk in the oil pan or the plastic teeth on the cam gear shearing off, ect... Regards. Ricky.
Most often, in my experience, it is not crank bearings but cam bearings. More than a little difficult to remove... Wouldn't be much more to go all the way. Just my $.02
I did just what u r saying but with a chevy click on my signature model a build and look at the pics tward the end of the post.
I agree with the notion that something is plugging the pickiup screen. Is the oil filter in good shape? Saw one 40 years ago on a 60 chevy that was gunked up and caused a similar problem.
I've done a lot of Fords with pressure problems. Generally It will need main and rod bearings for sure. If you see brass on the bearings there gone. Also replace the pump if you see scratches or scuffing on the gears, or loose tolerances between the gears. Most of this can be done by droping the pan and rolling the mains out. Use a brass pin in the oil hole and slowly rotate the crank, cleet first, roll out the old and roll in the new uppers. Unless the engine has been run with dirty oil the crank will be fine. A couple of hours and your good to go, even better on a lift. And use Cleveite Bearings, and pack the pump with grease for a good pump primer. Iceman
ConceptVehicleDesign and yardgoat, hit the nail on the head. A lot of people forget to check the Cam bearings.
Drop the pan and check the bearings. If they are OK, try a new oil pump. If they are shot, mike the crank. If it's worn badly, you know what comes next! I have done a few bottom end jobs like you describe, most times they work out fine, but when they don't, it's really annoying. It can be a chore to swap crankshafts on an engine with the pistons and rods still in the block. Sometimes a journal takes a beating from the rod bolts.
Thanks for the info, it is much appreciated. To answer a few questions: it's a '95 roller cam block from an F150, I installed a new cam and valvetrain along with a new timing set, about 70k on the motor over all and I didn't go into the bottom end at the time because it ran great and didn't have a ton of miles - relatively speaking. The cam bearings weren't replaced either for the same reason but I suppose they could be to blame. The gauge is a mechanical unit I picked up from Summit Racing. I also just changed the oil with a Napa gold filter and 5w30 Castrol GTX. I'm going to drop the pan this weekend and take a look.
we had a Cadillac do the same thing.. it spun a main bearing didn't make any noise just had erratic oil pressure readings, i would suspect that that is the case with yours too.. back it up with a mechanical gauge.. if its the same pull that crank i would bet money it was the same thing.... any grit in the oil?
What you're describing isn't an issue (IMO) with bearing tolerances...any time I've had worn bearing, IDLE pressure is lower and increases with RPMs. I'm thinking the pickup has come off/loose. Also, pump releif may be bypassing under load, but would be odd to happen on a newer, low milage engine?
It could very well be the pick up screen or oil pump. I am suspecting the bearings since it only does it under load and only when the motor has warmed up. I can drive it for 10-15 minutes with no problems at first, then the needle on the gauge starts to jump around a bit and flatlines. I'll pull over and shut if off for a few minutes and when I restart the motor, it reads full oil pressure again. Drive it a little ways and it starts jumping around again. I've checked it with a different gauge and get the same thing. Perfect when it's cold, jumps and flatlines when it's warmed up. Guess I'll know more when I pull the pan.
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