Connecting Rod Bearings?

SupraDave · 08-22-2005, 03:57 PM

I have a serious question for the experts. My car is a 1986.5 w/ 7mge engine and 5sp. manual trans., 80,000 miles.

I have some symptoms of bad connecting rod bearings.
1. 3-5 second knocking noise at startup. Knocking under load between 2500 and 3500 rpm.
2. Slightly low oil pressure.
3. metal shavings in the bottom of the oil pan.
4. using correct grade gas, car has new plugs, wires, distributor cap, timing is correct, no smoking from exhaust.
5. From what I can tell the rest of the engine is in good shape (good compression, idles well)

Can the connecting rod bearings can be replaced without pulling or lifting the engine, and how hard is this to do?

I don't have the money or resources to replace the engine but I do like this car and would like to keep it running well without spending a lot of money.

What are your thoughts?

monkihead · 08-22-2005, 04:52 PM

eh...i've done my oil pan gasket, which gives you a clear view of your rods. to my belief its possible, but only if your sure you can handle the job. i felt i was lucky enough to have a lift and a full set of mechanics tools at my expense. i sure as hell dont want to do it again, just like my head gasket.

SupraDave · 08-22-2005, 05:57 PM

monkihead...

did you need to pull the engine to get to your oil pan gasket? If you didn't pull the engine what did you need to remove?

monkihead · 08-22-2005, 07:53 PM

awesome pic!!!

okay, i dissconnected the motor mounts. i loosened the crossmember bolts but didnt remove them. i placed a tall stick styled hand jack on the crank balancer and raised as much as i could. fan shroud will hit.

im working on marking ur pic and will repost...
sorry ive got dial up

monkihead · 08-22-2005, 09:37 PM

rnoswal · 08-22-2005, 11:03 PM

Just my two cents but even if you can get to the con bearings, I would think that the crankshaft is damaged enough to warrant that it be ground. If there is any distortion in the rod journal, the the new bearings clearances will vary and probably be too close. Also the big end of the con rod will more than likely be out of round too and you can't get that out without pulling the head.

You really never now untill you have it apart and can get both pieces measured, but after going though all the trouble of getting the pan off, there isn't a lot more left to pulling the engine. You really do need a mechanical oil pressure guage too. The stock guage reacts so slowly it is hard to tell what it is doing at the more critical times, especially when it is hot.

Again, just my two cents worth.

Russ

monkihead · 08-23-2005, 02:52 AM

yeah, out-o-round can be a problem. however, some sbc guys can get away with it by polishing the crank with some emry cloth-if its not too bad.

suprra_girl · 08-23-2005, 08:36 AM

i would just yank the engine out....

take this time as a rebuild time and get a beater car

or... rip it out.. drop the sump... get the crank measured... if all seems alrite to your reconditioner.... get bearings specified... wack in... bolt up sump... wack back in

or... rip it out

pull the head.. strip the lot... rebuild the lot... new mhg, arps, rings, bearings et etc

it's up to you..

but honestly to do the rods properly you need to take the block, crank & rods to a machine shop and get it all measured

you may just drop in new bearings... but it's an unknown to how long it will last... it may be fine... in a couple of months it may knock again

it's a risk

how loudly is it knocking?

rnoswal · 08-23-2005, 02:12 PM

She is right as I wrote before. I have had guys put fresh bearings in some cars and they worked but the bearing looked worn but very evenly and had not been knocking. The others that tried it just ended up with the same problem. You can have someone measure the journals if you take the pan off, but man that looks like such a chore that it would be easier to just do what Supragirl says and take it out and do it right. Believe me, you will be much, much happier, except for the pocket book, but you are going to pay anyway.

If you insist just trying to put bearing in without pulling the engine, you may be fine, but marginally. The symptoms you mention are not really bad, but that metal is usually coming from the bearing and sometimes that metal gets into the cam bearing and I don't think they can be machined. The cam bearing aren't really bearings but the machined surface on the heads for the cams to spin in. If you could get these machined then the shims will have to be readjusted for valve clearances.

Lasty, if the knocking isn't too bad at startup, try some STP or Lucas oil in the engine. They offer protection on startups and maybe it won't knock as much and get you around al little longer, but try thicker oil, 50wt racing oit works pretty well.

The engine I just got from an excellent 87 N/A had a 4 inch hole under the oil filter, combination of bad rod bearing, low or no oil and high revving on a weak engine, but there are some highly modified parts laying in the engine compartment that shouldn't be there.

Sorry to ramble, just got off work and ready for bed. Good luck and let us know what you think you might want to do.

Russ

SupraDave · 08-23-2005, 04:22 PM

I must give credit to the webmaster of the Cygnus X1 website for the pic.

As for the car...

I'll just use it for short trips until I can save enough money to get a remanufactured engine. I honestly don't think repairing the engine is cost effective since it's completely stock.

Thanks for the tips and information.

One more thang...who would you recommend getting an engine from and who should I avoid?

08-22-2005, 04:52 PM	#2
monkihead SP58GT Join Date: Mar 2005 Location: San Antonio texas Posts: 646	eh...i've done my oil pan gasket, which gives you a clear view of your rods. to my belief its possible, but only if your sure you can handle the job. i felt i was lucky enough to have a lift and a full set of mechanics tools at my expense. i sure as hell dont want to do it again, just like my head gasket. __________________ ....all you need is a small taste of success and you will find it suits you.... monique- better off dead

08-22-2005, 07:53 PM	#4
monkihead SP58GT Join Date: Mar 2005 Location: San Antonio texas Posts: 646	awesome pic!!! okay, i dissconnected the motor mounts. i loosened the crossmember bolts but didnt remove them. i placed a tall stick styled hand jack on the crank balancer and raised as much as i could. fan shroud will hit. im working on marking ur pic and will repost... sorry ive got dial up __________________ ....all you need is a small taste of success and you will find it suits you.... monique- better off dead

08-22-2005, 09:37 PM	#5
monkihead SP58GT Join Date: Mar 2005 Location: San Antonio texas Posts: 646	__________________ ....all you need is a small taste of success and you will find it suits you.... monique- better off dead

08-23-2005, 02:52 AM	#7
monkihead SP58GT Join Date: Mar 2005 Location: San Antonio texas Posts: 646	yeah, out-o-round can be a problem. however, some sbc guys can get away with it by polishing the crank with some emry cloth-if its not too bad. __________________ ....all you need is a small taste of success and you will find it suits you.... monique- better off dead

08-23-2005, 08:36 AM	#8
suprra_girl 7M POWAH! ;) Join Date: Jun 2004 Location: New Zealand Posts: 2,312	i would just yank the engine out.... take this time as a rebuild time and get a beater car or... rip it out.. drop the sump... get the crank measured... if all seems alrite to your reconditioner.... get bearings specified... wack in... bolt up sump... wack back in or... rip it out pull the head.. strip the lot... rebuild the lot... new mhg, arps, rings, bearings et etc it's up to you.. but honestly to do the rods properly you need to take the block, crank & rods to a machine shop and get it all measured you may just drop in new bearings... but it's an unknown to how long it will last... it may be fine... in a couple of months it may knock again it's a risk how loudly is it knocking? __________________ Please use the forum to ask your questions as they will get replied to much faster than pming me Pics of my build. "Good girls are just bad girls that don't get caught" Do a diagnostic first!

08-22-2005, 03:57 PM	#1
SupraDave Stock Join Date: Jul 2005 Posts: 11	I have a serious question for the experts. My car is a 1986.5 w/ 7mge engine and 5sp. manual trans., 80,000 miles. I have some symptoms of bad connecting rod bearings. 1. 3-5 second knocking noise at startup. Knocking under load between 2500 and 3500 rpm. 2. Slightly low oil pressure. 3. metal shavings in the bottom of the oil pan. 4. using correct grade gas, car has new plugs, wires, distributor cap, timing is correct, no smoking from exhaust. 5. From what I can tell the rest of the engine is in good shape (good compression, idles well) Can the connecting rod bearings can be replaced without pulling or lifting the engine, and how hard is this to do? I don't have the money or resources to replace the engine but I do like this car and would like to keep it running well without spending a lot of money. What are your thoughts?

08-22-2005, 05:57 PM	#3
SupraDave Stock Join Date: Jul 2005 Posts: 11	monkihead... did you need to pull the engine to get to your oil pan gasket? If you didn't pull the engine what did you need to remove?

08-22-2005, 11:03 PM	#6
rnoswal Lexus & 550's Join Date: Apr 2005 Location: Bossier City LA Posts: 556	Just my two cents but even if you can get to the con bearings, I would think that the crankshaft is damaged enough to warrant that it be ground. If there is any distortion in the rod journal, the the new bearings clearances will vary and probably be too close. Also the big end of the con rod will more than likely be out of round too and you can't get that out without pulling the head. You really never now untill you have it apart and can get both pieces measured, but after going though all the trouble of getting the pan off, there isn't a lot more left to pulling the engine. You really do need a mechanical oil pressure guage too. The stock guage reacts so slowly it is hard to tell what it is doing at the more critical times, especially when it is hot. Again, just my two cents worth. Russ

08-23-2005, 02:12 PM	#9
rnoswal Lexus & 550's Join Date: Apr 2005 Location: Bossier City LA Posts: 556	She is right as I wrote before. I have had guys put fresh bearings in some cars and they worked but the bearing looked worn but very evenly and had not been knocking. The others that tried it just ended up with the same problem. You can have someone measure the journals if you take the pan off, but man that looks like such a chore that it would be easier to just do what Supragirl says and take it out and do it right. Believe me, you will be much, much happier, except for the pocket book, but you are going to pay anyway. If you insist just trying to put bearing in without pulling the engine, you may be fine, but marginally. The symptoms you mention are not really bad, but that metal is usually coming from the bearing and sometimes that metal gets into the cam bearing and I don't think they can be machined. The cam bearing aren't really bearings but the machined surface on the heads for the cams to spin in. If you could get these machined then the shims will have to be readjusted for valve clearances. Lasty, if the knocking isn't too bad at startup, try some STP or Lucas oil in the engine. They offer protection on startups and maybe it won't knock as much and get you around al little longer, but try thicker oil, 50wt racing oit works pretty well. The engine I just got from an excellent 87 N/A had a 4 inch hole under the oil filter, combination of bad rod bearing, low or no oil and high revving on a weak engine, but there are some highly modified parts laying in the engine compartment that shouldn't be there. Sorry to ramble, just got off work and ready for bed. Good luck and let us know what you think you might want to do. Russ

08-23-2005, 04:22 PM	#10
SupraDave Stock Join Date: Jul 2005 Posts: 11	I must give credit to the webmaster of the Cygnus X1 website for the pic. As for the car... I'll just use it for short trips until I can save enough money to get a remanufactured engine. I honestly don't think repairing the engine is cost effective since it's completely stock. Thanks for the tips and information. One more thang...who would you recommend getting an engine from and who should I avoid?

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