79BFN

Lots of time has passed and this project has still not been completed.
I can only start by saying I was able to use the boat a few times in 2009 or until the last weekend in August............. That's when I lost oil pressure pulling a friend skiing. I didn't really have the funds to fix the motor right away and was really just burnt out on the boat, so I let her sit in the shop. I was never really impressed with the performance and thought it was probably just my overall experience with the smaller 81SN I had for years and the difference in the two boats.

I was in no hurry and did finally pull the motor last year and tore it down to discover a crank that was worn beyond belief. I had one rod journal that had an 1/8" lip on it......egg shaped to the extreme. So much for what was supposed to have been a fresh rebuild when I got it! Guess I should have known otherwise when I saw the HEI distributor in the thing.

I didn't take any pics of that crank, but did get a used takeout from the local HP engine builder (his customer was having him build a stroker motor and the old crank had never been turned.) After having him align bore the block, resize all the rods (including 2 new rods), balancing the whole assembly and building the short block, I gradually went back to work assembling the rest. I had her all back together in October but to burnt out on it to stick it in the water and give it a try.

Well today I fired it up. I'm still disappointed! I took it easy for about 30 minutes and when I say easy.....never over 3000rpm. I launched from a stop a few times but did not WOT at all. There were a few ticking sounds comming from the valve covers and seemed to come and go at diff. rpms. The oil pressure was steadily above 50psi and mostly up to around 70psi. I felt pretty good about it other than this persistant vibration around 2000rpms. Actually, that is just where it is at it's worst. I thought I felt it throughout the rpm rise, however, my buddy says it feels smooth to him other than at about 2000rpm.   So.....trying to remember exactly what I had done before, I did have the refurbished prop on the boat and may possibly have some shaft alignment issues and the worst case scenario would be I need a brand new prop. After weighing all this out and giving her a little time to show signs of weakness, it was time to give it a WOT pull down the cove in front of the house.

Well, she's knocking now. After pulling back on the throttle, oil pressure was below 20psi and a knock had developed. I pulled her over to the dock and just let her idle for a bit before shutting her down. I did fire back up to load on the trailer and the knock was gone and oil pressure was back up above 50psi......but I'm nervous now. The last thing I want to do is pull this motor again!

I've thought about a plan all evening and have finally come up with one. First thing I'm going to do is drain the oil and remove the filter. I'm going to cut the filter open and see if there is bearing material and I'll of course strain the oil as well. If all looks good, I'll fill er back up and give it another shot, if not, she'll be comming back out.

I do have two questions for any of you that may have an OMC454.........
What max rpm are you turning?
How much oil capacity total between filter, hoses, and oil pan are you putting in your motor?

Kurt, sorry to hear youre still having troubles after all the hard work you put into the boat!

I would imagine that OMC and PCM were sourcing the same GM longblocks, so I would refer to the PCM manual in the reference section. It says that the oil pan capacity is 5 qts at the 15* installed angle. Add the filter, and Id say youre in the 5.5 to 6 qt range.

As far as WOT RPM goes, 4400 is typical on the stock 330 hp BFN's Ive driven with the stock prop. That will probably yield the best all around performance. That being said, the 454 bottom end is supposed to be very strong, even if youve got 2 bolt mains. I wouldnt worry about spinning it 5000 or beyond (though that would not result in the best performance unless you have an upgraded top end). We've got 4 bolt mains in our 454, though Im not certain its the original block... we spun it 5200 without issue and plan to turn it higher this year.

Ill let someone else with bottom end rebuilding experience chime in on the knocking and oil pressure issues, but Id say your plan of attack sounds pretty good.

the grinch wrote: Prop is a 13x15 I had refurbed. What is stock supposed to be? If I had a vibration that was only at around 2000rpm, would it be prop or shaft alignment related?

Did the prop shop do a complete balance on the prop? some don't have the equipment and will just do a visual on the bench block. Shaft straight? Prop seated and lapped to the shaft? Cutlass bearing OK?

That 13x15 Federal would have been the original prop. If properly tuned/balanced, it shouldnt vibrate significantly. That being said, an Acme 1598 is a really nice upgrade for that hull/engine combo... you'd see improved performance and it would be a bunch smoother.

Like Pete said, check the rest of the drivetrain too.

I sent the prop somewhere down in Fl. I'd have to look up where, but I can tell you when I put it on it made a huge difference. I did not lap it to the shaft. Would this make a big difference? I did replace the cutlass bearing and the shaft was new when I bought the boat. You could look through my posts and see how bad the log was and probably was so bad due to something serious involving the shaft. The coupler is original as I can best tell.

As far as the notches go on the pistons, my understanding was always that what should make this determination is how they are attached to the rod. The reason for this is so that you know which side of the rod has the chamfered side on the journal. If you don't have the chamfered side of the rod toward the outside of the crank journal, your bearing will wear on the chamfered edges of the crank and not to mention, probably be in a bind.

Kirk,
I suggest you check the shaft for straightness especially aft of the strut. You haven't mentioned anything about it.

Motor is back in and her problems were........................OMC oil pan sump holds 9qts! I had 6.5 qts. total including the remote oil filter. This is why the big drop in oil pressure after a WOT pass. Good thing I pulled her, no harm was done to the bearings, but found something else......3 lobes on the camshaft wiped out. This was the camshaft and lifters in the motor when I purchased it and was supposed to be new. I didn't even look at it last year when I took the block to the machine shop. So, I have a new cam and lifters and she's broke in after this weekend and plenty strong.

I still have a slight vibration in gear at rpms below 2500.
I pulled the prop and then lapped it on making sure the key was not causing it to ride off the taper. This helped, but still have a vibration......................I'm thinking shaft at this point. I am going to buy a new one anyway. Any recommendations on which one to buy and who to buy it from? Should I put in another new cutlass bearing while I'm at it? It probably has less than 15 hrs. on it.

Ok.......removed the shaft and chucked her up in the lathe. Looks like it's out about 14thousandths. I am really more interested in the combined runout with the coupler installed. The best I could get the coupler in the chuck I had a 5thou variance, but I need reversible jaws to get it any better. Nonetheless, I put the shaft in with the key and set screws and saw variance of 26thous. I messed with it a little while and got it down to 20thous. How do any of these boats with the factory coupler, w/ keyway & set screws, not vibrate?

So.....looks like I'm ordering an ARE double taper. One day and hopefully in the near future, I'm going to be done spending money on this project.

Ordered the shaft today from Elbert's. He said the factory spec showed 41" length shaft. Mine was 41.5". I ordered it of course, before reading your post and told him the 41" would be fine. What effect would shortening it do? It seemed awfull close to the hull as it was and at some point it has hit the hull. Or, I should say something has hit the hull in that area because I had to repair it.

I went ahead and ordered a new ACME 1598 13x14. I'm going to install the new shaft and try her out first with the old 13x15 and see how things go and then give it a shot with the new ACME. I'm beyond frustrated but I hope the end is near.

Have you taken a look at your spark plugs? Burning evenly?

the grinch wrote: If I have something goofy going on here, wouldn't it also show up at WOT?

Maybe, maybe not. There are a few variables. Give them a quick look and note where they came from. I think a miss will amplify out to the prop.

This may not be your problem, but it's an easy check.

And don't get frustrated until you've rebuilt the top end on the dock.   

did you have both faces of the coupler checked?

What's the chances I may actually have an ignition problem? If you look back, you'll note that the boat had a HEI from a car in it when I bought it. I replaced it with a Pertronix and followed the installation instructions and messed with the hacked up wiring and finally got it to work. (No ballast resistor) I'm wondering if I might have a resistor wire feeding the coil. I'll bring home the meter tomorrow and check out the voltage. Since the boat is running great above 2200rpm, could it have something to do with the mechanical advance in the distributor kicking in at about that rpm?