OMC 4.3 knock at idle

[whickety2007]

Hi all...I'm new to the forum, but have been reading it off and on for years.
I'm sure someone has a diagnosis for me.
Here is my problem:
I was given a 1989 seaswirl about four years ago with a cracked block and heads. (wasn't winterized, and it cracked everywhere....even the exhaust manifolds. I thought I "learned" the hard way by replacing the long-block (block, and heads) with a junkyard special. All of the marine peripherals were reused.
I ran that motor for half a summer, and ended up spinning a bearing, and seizing it I then purchased a GM crate 4.3 truck longblock which is pretty close cam wise. I placed brass freeze plugs in it, and once again reused all of the marine peripherals (alt/start/intake/carb/oil pan etc) and have enjoyed it for the past 2 seasons. I ran it in slowly, jumping it on plane quickly not to overtax it, and varying the throttle speed for the first 20 hours. It still has good oil pressure 20-40 at idle, and 50-60 at 3500rpm depending on engine temp. It has never overheated.
It recently devoloped what I'll call a knocking noise at idle. It just runs a little rough below 700 rpms and a light knock like the timing slipped. (it didn't I checked it) I thought, at first is was the esa system (which has never worked) actually malfuntioning because of the fact that over 1000 rpms it seems to sound fine. I took it into my local marine mechanic, and he pulled the drive. He advised that the low speed knock seems to have gotten better, but its still there. ( i had replaced the gimble bearing with the original install two years ago. either way the drive has been eliminated as the source) He also thinks the alignment, and u-joint is ok. He thinks the engine coupler, or flywheel has come loose, and wants to pull the engine. Now I know that I torqued the bolts right, and used loc-tight red on the threads. So is there a better way to diagnose the knock/rumble?
Also he wants 4-500$ to pull the motor...sound reasonable?

 

[whickety2007]

Re: OMC 4.3 knock at idle

Ok... so now I'm desperate for some help.
The shop I'm working with has pulled the engine,and the news is not good.
I stopped by and he walked me through what he found.
He removed the pan and found some metallic material in the pan. Its very fine and not that much, in my opinion it seems like what you'd find after break-in. Just a fine film on the bottom of the pan
The main bearings are scored as well as the crank journals. Just enough to feel with your fingernail. (Yeah I know very scientific huh) It seems to me they should still have a very highly polished finish. Nothing seems discolored like it overheated, and it has always run cool. The rod end caps were not pulled off. He also pointed out some cylinder wall scuffing on the base of 2 of the cylinder walls. It seemed insignificant to me.
He wants to send it to his machine shop for a complete rebuild and quoted 1500-1900 for this.
Why would a remanufactured engine show this much wear/damage after just 40 hours of operation? With lightly scored journals, would installing a new set of bearings get me through the rest of the season?
I go on a lake vacation the week after next, and it will be worthless without
a screw turning in the water.
Any comments would be appreiciated. Thanks

 

[79Glastron]

Re: OMC 4.3 knock at idle

I guess a new user is going to help another new user!
Geez...thats hard to believe with only 40 hours on it. You said he didn't pull the rod caps yet? I think I would plasticgauge both the mains and rods to see if there is excess clearance, and if so why, mic crank. IF the crank is ok, not too badly scored etc, I would throw in a new set of bearings, but making sure they are set correctly. I guess GM can't help you because the motor was used in a boat not a truck....too bad. Let us know what happens.

 

[whickety2007]

Re: OMC 4.3 knock at idle

Thanks for the reply...The mechanic is at a loss also. He has stated that it seems as though i did everything right, and maybe just got a bum reman.

I did some digging, and in the corner of my garage I found the original engine's
innards! Crank, main caps, pistons (still on the rods). I even have the cam, roller
lifters, pushrods, and rockers. Like I said the original had cracked, but these parts all look to be fine, the journals still pretty nice and smooth. Although there was a slight amount of surface rust here and there (one rod journal had some corrosion on about one third of it) it cleaned up with some wd-40. and 800 grit wet-sand paper. The wrist pins are tight with no slack while twisting them.
I don't think any of these parts have been machined, and should be at original specs. The cam. i think is not interchangable as it is a roller, and the current engine is not.
My obvious concern is the bottom end, specifically the main, and rod bearings.
Should I take another chance at putting these reciprocating parts into this block? I think I'll take all of my parts into the shop, and see what they think.
Meantime...does anyone out there think i will get legitimate time out of this motor, or am I just waiting for it to grenade?
I have read that 800 - 1000 hours is not unheard of with what is basically the venerable Chevy smallblock.

 

[gwaidman]

Re: OMC 4.3 knock at idle

Well, I'm no engine expert, but heres my 2 cents for what its worth... The mains should be smooth, a ridge enough to catch a fingernail on is too much, and should be polished out. If it were me, I would have your old crank mic'ed at the machine shop and polished out (.010" - .030") and toss in some new main bearings. Run it on your week off and have a great time! On a side note, any chance that the knock you are hearing is piston slap?

 

[whickety2007]

Re: OMC 4.3 knock at idle

Yup going to take the old crank into him today, have it measured properly, and
polished/resurfaced if need be, and installed By piston slap, what do you mean? Excessive clearance at the wrist pin, connecting rod bearing, or cylinder wall?
Also, does anyone know if a crankshaft can be installed without removing
the heads. I don't think so, but I'm not sure.
Thanks

 

[MikDee]

Re: OMC 4.3 knock at idle

Just a note here, you cannot use the main bearing caps from another engine, the caps are specific to each engine, Unless you put them on and have the block "line bored" to fit. You can possibly use the crank, but have it mic'ed up to be sure it's neither engine is not undersize, then you'll need to get oversize bearings. The same goes for the connecting rods, and piston's, if you're dealing with a factory rebuild, the piston's could be slightly oversize as well. Just make sure if you're switching part's around that you mic. it all up and get it all to match. One more thing, IMO, I don't know where you got the rebuilt engine from, but I doubt you did that crank damage at 40hrs? I think it came that way, and is only now showing it's faults after all the "slapped on" new parts are worn in.

I had a 74'Nova SS 350 motor that came new from the factory, that had all the bearing journals .001 undersize! It was discovered at rebuild time, I was gonna put in standard bearings, until the guy from the machine shop noticed it, and stopped me, I would have had no oil pressure!

By the way, you have to take your heads off, on most all engines the piston's go in from the top. Except for an old 70hp Merc 6cyl. outboard I rebuilt 40yrs ago, that had no head, just an integral block, they all went in from the bottom! That was a handful, to say the least.

 

[bruceb58]

Re: OMC 4.3 knock at idle

Just one question out of curiosity...You said that you bought a crate engine and then later on you said it was remanufactured...I always thought a crate engine would be considered "new".

 

[gwaidman]

Re: OMC 4.3 knock at idle

Piston slap = excessive piston to cylinder wall clearance. Very small numbers and it usally goes away once the engine is up to temp. The GM 5.3 and 6.0L engine in the last gen trucks are famous for this noise. Its not really all that terrible, and lots of engines have it and run for quite some time.

I believe that you should be able to swap the crank with the heads on. You will have to pull the plugs out so you can turn the engine by hand!

Good luck!

 

[whickety2007]

Re: OMC 4.3 knock at idle

Thanks for all of your responses.
I will have all of the parts mic'ed up for a match, and will use the existing main caps.
I guess I was using the term "crate motor" as a generic meaning.
The longblock I put in it was a remanufactured engine.
Apparently you get what you pay for...

 

[whickety2007]

Re: OMC 4.3 knock at idle

Ok, so I dropped the old crank off at the repair shop.
The mechanic really didn't see a problem installing it if it measures out ok.
Thing may be looking up
2 rod journals are in question with a small amount of pitting from some surface rust, but he seemed to think it would polish out.
He is going to pull the old crank and mic the main, and rod holes, and mic the "new" crank journals. Hopefully the block will need no machining, I he will just be able to install the correct over or undersized bearings.
On another note, I was trying to understand why thee bearings would have failed, and remembered that last year I was getting a heavy gas smell out of the oil. I thought the fuel pump diaphram may have failled, but it checked out fine.
So I have changed the oil a few times without the smell returning.
Could this have been due to break-in, and a lot of blow-by during break-in?
Now that the rings have seated themselves, this blow-by is not an issue?
Has anyone had this problem, when breaking in a Chevy?
Sorry for all of the questions, but YOU guys have the answers...I've seen it time and time again in this forum.
Thanks.

 

[RCSConstruction]

Re: OMC 4.3 knock at idle

Sounds like the engine was not put together totally clean. Seems like some junk got into the journals. Assembly grease will leave that "metallic' residue in the oil. Usually takes 2-3 oil changes to get rid of it. Some builders I see use a S-load of it.
Was the knock emanating from the side or top of the engine?
What blend oil were you using for break-in? 10-40,5-30,15-30,30w?
A lifter or valve will knock most at idle disappearing as the RPM's raise, where a rod knock would normally become louder.
Get that crank balanced, true'd, and re-ground. Don't ***** foot around with a polish. Get the matching bearings and you have a brand new bottom end. Should be around 125-150 for the crank and another 50 for the bearings.

 

[whickety2007]

Re: OMC 4.3 knock at idle

The knock was coming from down low on the back of the engine.
This is what led us to believe it was the flywheel, coupler, or drive.
It seemed to go away completely as rpms would approach 1000.
I frankly didn't think the knock was that bad, and basically just wanted to be able to turn my idle back down to the 6-700 rpms range. 1000 just had me coming into the docks too fast, and I struggle to shift it out of gear at that speed idle because my "famous" OMC esa module has never worked.
I run straight 30 weight nothing else.
Do you think I should request the mechanic do a leakdown, or compression
test before removing the old crank?

 

[whickety2007]

Re: OMC 4.3 knock at idle

RCSConstruction...I think you got it.
My mechanic took my old original crank to the machinist today, and the news is good. It is compatible with the block I have, and will require minimal machine work to fit it. The machinist thinks that the motor was put togeth dirty as well, and actually thinks the knock was coming from a piston.
My mechanic is taking off this weekend, and won't be back unit next tuesday.
So I stopped and had him load the motor into my truck. Once home, and on my stand I tore it down...and think I royally screwed up when putting it together three years ago. At the time someone, had mentioned coating the lifter valley with Glyptol Red paint for better oil flow, and I did. I had forgotten about this until I pulled the intake tonight. There was a lot of this material loose in the block!
So I'm pretty sure it got into the main journals.
So since I'm under such a tight time line to get this boat back in the water. (I have a finger lakes cottage rented for all of next week) I need to get this block
cleaned up and to the machinist tomorrow. The heads, lifters, lifter bores, pushrods, camshaft, camshaft bearings all look great. The cylinder walls look pretty good, with some cross hatching still visible, maybe some light scuffing, but I'm sure a light honing will clean them up proper. The pistons look really good with minimal vertical scuff lines.
Now what can I use to wash this block out?
Can I disolve this Glyptol coating with paint remover, or solvent of some type?
How can I get all of the oil passages clean? Pipe cleaner, and some patience?
I do have a compressor, so blowing out passages won't be a problem.
Thoughts? comments? I'm very open to all.

 

[RCSConstruction]

Re: OMC 4.3 knock at idle

Take it to the same machine shop that has your crank and have them "hot tank" it.
They will clean that block BARE in a matter of 20 minutes. Should be real minimal cost, if not free.
Good luck with the rebuild

P.S.
On second thought, the cam bearings will be damaged with the hot tank, if the block is as dirty as you say I would hot tank it and have new cam bearings installed. Again minimal cost but I know it's starting to add up.
If you didn't want to go that route I would get the berrymans Chem dip. It's a 1 gallon can and will do the job. Don't forget to remove the oil passage plugs, so it can be blown out properly.

 

[whickety2007]

Re: OMC 4.3 knock at idle

Thanks once again for the reply.
I just dropped off the block with the machinist.
Its looking pretty good. He noted only minimal scuffing of the cylinder walls,
and pistons. He is going to hot tank it tonight, and let it soak until Monday.
Monday he will mic out everything and install new cam bearings.
He is going to supply me with new main/rod bearings, the refinished crank and clean block. I will then have to reassemble everything, and get it back to the boatyard for reinstall. This, of course is if all of the planets align, and the big
man upstairs is watchin over me.
Oh, by the way, the glyptol coating that I put in the lifter valley was the culprit so says the machinist. Its hard for me to think this was self inflicted!
Live, and learn I guess. "BOAT" bring out another thousand right?
I think my next one will be an outboard!

 

[whickety2007]

Re: OMC 4.3 knock at idle

Progress:
I picked up the block/crank, and all of the new bearings/ring Monday night.
The machinist honed the cylinder walls, and installed new cam bearings.
The pistons measured out fine, along with the rod and crank bores.
I spent about 14 hours yesterday assembling everything.
I took it especially slow with the bottom end, following a Chevy assembly
manual step by step. Time to deliver it back to the boat yard for install, and
startup, well with any luck it will start.

 

[93 Regal USAF]

Re: OMC 4.3 knock at idle

Progress:
I picked up the block/crank, and all of the new bearings/ring Monday night.
The machinist honed the cylinder walls, and installed new cam bearings.
The pistons measured out fine, along with the rod and crank bores.
I spent about 14 hours yesterday assembling everything.
I took it especially slow with the bottom end, following a Chevy assembly
manual step by step. Time to deliver it back to the boat yard for install, and
startup, well with any luck it will start.

Please keep us posted on how thkngs turn out. I've found this to be a very interesting thread, and I have tried to learn as much a my brain would allow!

Good Luck!

Joe

 

[MikDee]

Re: OMC 4.3 knock at idle

You did get new rings in the proper size, and installed them right, didn't you? along with the new bearings, and did you clean, or replace your oil pump? What the hell is glyptol? It appears that did your engine in! It sounds like you finally did the right thing, Good Luck, Mike

 

[wire2]

Re: OMC 4.3 knock at idle

Glyptal is an insulating varnish manufactured by G.E. It's commonly used in the manufacture of electric motors and electrical parts. It dries very smooth and is impervious to petrochemicals.

It's a high performance trick to coat the rough texture of a sand cast engine block to keep the oil flowing back to the sump faster.

It's not supposed to get into moving parts though, as it inadvertently did here.