Howdy, I'm new hear and hope I can get some help. I'm I blues musician, piano tuning Mopar lover!
Found a boat that had a 72' 340 Chrysler marine engine. Same engine I had in a 72' Challenger I had many years ago. Spent last winter rebuilding engine. First time I tried rebuilding an engine. Learned a lot, screwed up a lot also.
First engine test run water to hot engine over heated. Second test run without thermostat ran great but to cold. Should be about 180F but ran about 140. good oil psi.
tried a test run on water to put load on engine. Still no T-stat. boat ran great and I cruised around for half hour at 2500 rpm all was good. WOT or red line is around 5000rpm, I could not help my self so I pushed up to 3000 rpm and my little 18 foot Sutphen was doing close to 45mph. Wind in hair beer in hand life is good until I look at oil temp which is at 280, water temp is still at 140 or 160. I bring her back to 2000rpm and oil temp comes back down.
got her home. Oil was black and burnt, no metal fragments. Changed oil and filters. Ran her again in the water same results but worse. when pushing above 3000rpm the water temp is fine but oil temp jumps up. I cut engine down to an idle but I could hear some scary squeaky sounds so I cut the engine.
Got her home, oil again was black and burnt. Changed oil again. Started engine but it sounds like it is laboring, does not idle as well. when I rev her a bit she sounds ok when going up in rpm's but coming down I hear some rattling or light knocking. I don't hear any squeaky metal on metal sounds but she don't sound good. Also oil psi is to low only around 20psi should be around 50 or 60. still no metal in oil. I think I my have spun a bearing Or messed up my lower end some how.
Any thoughts on what to look for? Im gonna pull engine this weekend.
Sorry for being so long winded.

 

It does sound like you did some damage ? I would pull the pan and check the bearings. Did you replace the water pump ?? May need a marine specific ? reverse rotation ???

 

Sucks man. Ever burnt olive oil in a pan on your stove, leaves a varnish that's tough to remove? Expect the inside of your engine to look like this. I have no idea the cause of your issue, good luck.

 

off the top. sounds like the bearings are to tight. but not to the point to damage the crank / bearings. as you put the engine to gather rotate it to check for binding.

 

I think your right.
I had trouble with the number 3 main cap and bearing. I spent a week trying to figure out why, when torqueing the #3 cap to 60 lbs the crank would turn to speck but when I tightened to 80 lbs which is to speck the crank would only turn at at 40 lbs (speck is 15 lbs).
After much frustration I decided to torque cap to 75 lbs and hope for the best. Bad decision!!! I think its come back to bite me?

 

The bearing cap torque should have not one thing to do with bearing clearance. That is, once you get the caps seated, you could probably tighten them to 30 ft lbs and the clearance would measure the same. The bolt torque is to hold the caps on and in alignment, not for clearance

I agree with the above. Something is amiss, probably crank / bearings. Time to pull it and tear it down. Hope you did not ruin the block and have to have it "align bored." Properly known as "line bored."

Same deal with the rods. Check, re-check all of em carefully.

 

That sound like it might be the problem area......

Most Cranks turn pretty free unless you use gobbs of heavy lube on them.

The oil turning black... That sounds to me like, there is an additive in the fuel the motor dosent like? or that the ring have not seated properly and your getting allot of blowby past the rings.

When you talk oil temperature, You get a wide spread.... Something like 140-220 DEG. There is allot of factors that come into play there. I don't think that ( I have ever) gotten a general across the board answer for that question. Just to many variables. But would I con-ceder 280* high for oil temp... YEP In my Book!!!
The few boats that I have worked with... I look to keep water temp around 160* on the average. and if i'm not mistaken the oil temps have hovered around 80-90*....

 

thank you all for the help and direction. I will let you know what I find.

 

Possible thrust bearing not seated front to back with BFH?

 

i cant say iam an engine guru. but check the caps for being cracked. that would let them flex when torqued. or stripped threads. what think bob?.

 

the thrust bearing was within speck front and back. I think speck is .002 to .007. machine shop said the same thing at the time of assembly. He suggested I rap the end of crank with brass mallet with caps in place and tightened. I tried it to no avail.

 

I forgot to ask, what does BFH mean?

 

some shots. 1972 Sutphen. Came with the 340. Chrysler Marine called the 340 the Super Bee III. The 318 was called the Super Bee II.

 

I'm curious where your oil temp sensor is?

Oh and the other thing is a Big Fargin' Hammer.

 

Oil temp sensor is on the side of the pan.

 

The crank could be bent ??

 

U could have a main cap fliped or on backwards also a rod cap can be back wards,
just some details to look for.

 

You never know until you look...

 

When hearing about your 60 ok then 80 not ok ft/lbs I'm thinking at 60 maybe the #3 cap was not down and seated and at 80 it was.

This would show bent crank, misaligned main bearing bores or improper bearing register or crush.

If you get to taking it apart you could leave heads on remove rod caps and slide pistons up with rubber hose on the rod bolts to get at the crank for inspection without a total tear down.

If your very careful taking 2,3+4 caps off and sliding there upper bearings out, with the chain off and a dial indicator you could check crank straightness on #3.

 

I think there is still a blowby issue that needs to also be looked at also.. Still.
Oil only turns black with combustion....

 

Not knowledgeable about marine applications, do they have typical crankcase ventilation?

That's a lot of blowby, got me puzzled.

 

I recall seeing burnt, black oil once when an engine ate a camshaft real bad!

 

Hummmmm,,, I guess I stand corrected.....

 

Hope I'm not too late to this discussion but marine engines running hot and spinning bearings after being rebuilt to car specs is nothing new. The boat gets unrestricted water and runs too cool when the valve is all the way open. The OP stated that at first it was too hot, then too cool. That usually indicates that he opened the water shutoff valve all the way and at RPM the boat pulls too much water from the lake/river to pre-heat it before it reaches the engine. While the heads are nice and cool, the pistons, rods and bearings still have all the heat from combustion being absorbed. This causes them to expand and really tightens things up in the bearings and piston bores. As a result oil temps tell the true story and that engine was extremely hot. Usually we leave a little extra clearance on marine engines.

Yes I think this engine was hurt, it could be hurt just a little, but usually they are hurt quite a bit when this happens. It is possible to score cylinder walls, wipe out cam, rod, and main bearings as well as bend rods. At the very least, I suspect you took out all of the bearings.