8.1 496 reliable build questions
 

This is a little off base for this forum but this looks like the forum with the most knowledge of these engines. I have a 25' Carolina classic offshore fishing boat. Weight is 12000 pounds loading for kill time offshore. It has the Volvo 8.1 with the standard water reversion thru the exhaust issues with engine failures around 500 hours. So I am getting ready to build another engine for this boat the donor is another Volvo 8.1 that has kicked the bucket from stuck valve hitting piston only 450 hours of run time on it. My plan is forged pistons to get rid of the problematic factory pistons, stainless valves and bronze guides in factory heads if possible, arp head bolts or studs, and then stainless marine exhaust with custom risers which he has made numerous sets of these for my style boat and it seems to be doing the trick to get away from water reversion in the exhaust. I am looking at staying at the 375hp level as it works well with my boat. I just want a reliable engine that is going to go 2000 hours. Where are places I can source these items or any thing else I would need. Thanks in advance I am located on the eastern shore of MD near ocean city.

you wont get 2000 hrs from a gas piston engine pushing 12K.....diesel maybe

Jegs, Summit racing are parts depots

You might want to downgrade the cam a little bit. You probably never use full throttle anyway. Of course, cams for that guy aren't easy to find, but you could-I believe-run a standard big block cam in it. I have a couple of gen 6 stock truck cams if you want one.

I'm running Scat H-beam rods and SRP forged pistons in my 496. Pretty sure the cam in the 375 HP version of that engine is close to the stock 8.1L truck engine cam. Not sure how you could get much more tame than what is already in there.

Well maybe not 2000 hours but more then 500. My last boat was similar in style and weight with a 454 and it had 2600 on the clicker never did anything but tune up and maintenance and risers. I am really just looking at sources for a parts for the build and any insight if I should do any different. The stainless Mari e exhaust is going to take care of the reversion 99% sure as others that have it installed on exact same engine and boat have had no issues. The stainless valves and bronze guides are just a precaution since I need to have the heads done anyway. Any idea where to source stainless valves or will the machine shop have to find them.

have the machine shop get them, and put Inconel exhaust valves in them

Now with pistons should I forge or shouldn't I. Also will they work with stock rods. Will the inconel valves resist corrosion also like stainless. Sorry for the questions I just don't want to trip over a dollar to pick up a penny. I just want a rugged build that will last. If you were in my shoes with this how would you do it.

Inconel IS stainless, only the toughest, most corrosion resistant and most importantly most heat resistant stainless there is. From what I have heard, GM used inconel exhaust valves in their big blocks from 96 or so on. Worth looking into. Forged pistons? If you are replacing pistons, definately. And I knew a guy with 2 454's in a sea ray sportfish with 2000 hrs. I had a 30 IMP with 2 330 hp 454's with 1000 on them and ran fine.

What material are factory valve guides, if the valves are inconel from the factory why are they rusting a sticking then kissing the piston. Just a question kinda thinking out loud

never mind

If you stick with the stock heads and cam do like the other guys have mentioned- get forged pistons. The stock rods can probably handle it if they are checked. Have the heads tested and call Raylar to get a set of their roller rockers and springs. The stock springs are very weak and likely the problem of the stuck valves. Between the roller rockers, new springs and Stainless exhaust you should have a reliable package good for close to 1000+ hours which is what most 496's run in commercial applications regularly.

Good call on the valve springs didn't even think of those. Thanks guys for the info. Now the question about cam sensors comes to mind and what timing chain set to use.

Did I say something wrong here

100+ hours which is what most 496's run in commercial applications regularly.

What do you mean buy this.

no.....there might be a 0 missing on KA post

Edit: if your going to build an engine and expect it to last for many hours, it needs to be done by a reputable marine engine builder, all new everything.
oil pump, bearings, rings, lifters, check the block for square, line hone if need be, complete head rebuilds, and then the fuel system, clearances on bearings, lifter bores, and guides are not the same as a street application, good luck.

Fixed it 1000+

Stock

Replace both.

Genuine Mercury & Mercruiser parts

Are you rebuilding or a shop?

I am having all the machine work done all new bearings and everything checked balanced so on. Just looking for ideas on what is needed to be beefed up to make it last. I will put the engine together myself but having a reputable shop do all the machine work. And as far as timing sets I know there were 3 variations of sensors and sprockets and I know for the latest set I need to change out the timing cover to have it work and I think there is a pigtail that is needed.

Just a quick question while I have everyone's ears, my engine being the hp1 version 375hp what is different between it and a regular truck engine. Hard part wise are the cranks and cam the same?

Diamond and Wiseco make stock replacement 4032 forged pistons that are designed to use the stock rods. I would upgrade the pistons if rebuilding for peace of mind. ARP makes upgraded rod bolts for the stock rods. However, once you buy the rod bolts and resize the rods you've matched if not exceeded the cost of a set of Eagle/Scat H beams. Stock rods/bolts are fine at stock rpm levels.

Your machine shop should be able to source your valvetrain. Stock valvesprings are fine for stock cam/rpm levels. If you want to upgrade call Larry @ Raylar. Good guy with lots of knowledge on the 8.1.

Mercruiser 496's don't seem to have reversion issues. Maybe source a set of Merc manifolds/risers.

PT075H3 Wiseco

12705 Diamond

Same for the base 375hp model. 425hp model has larger cam and different PCM.

So if ever needed I can source a truck engine and marinize it and have the same thing I have now. I have kinda decided on just going forward with stainless marine exhaust and the custom risers he makes for my boat as it moves the water exit about 18" further back then stock risers. Thanks for the quick responses.

If you have a stock Mag motor. To do a cost effective rebuild, re-use connecting rods, install rings, pistons, valve springs and roller rockers and be done. I would use all stock parts then use forged pistons (diamond or Raylar), Raylar rockers and Raylar valve springs. If you change cam, you have to change ECU.

Dont start swappping truck parts, it ends badly - ask me how I know...

Yes I have a complete Volvo 8.1 375hp with 1 bad piston right now. I am looking to do a full set of pistons have the heads redone and what ever machine work needs done. I was just curious if a truck long block was the same specs as a 375hp long block.

So good information so far, this is the plan now with what I have received from you all. Stainless marine exhaust, forged pistons, valve springs and rocker arms, possibly go ahead and do connecting rods while I am in to it. And make sure I have inconel exhaust valves installed. This motor will never turn over 4500-4600 rpm and if it does that it is for a very short burst just to make sure she still has it in her. Next question is if I do the rocker arms and the ratio is 1.7-1 do I need to have anything done to my mefi 4 controller tuning wise.

You should only use 1 type of rocker arm from Raylar. They (496/8.1) require a different nut than other big blocks. All other rocker brands will require bigger valve covers due to the nut, different rocker nuts for a standard scorpion or crane, then you have to change the mounting of the valve covers then you have to change the mounting of the coil packs... If you use generic rockers and save $40 you will spend $500 getting the rest of the stuff to fit correctly. Buy the stainless rockers from Raylar and you are done - no other modifications. The 496 has metric studs. Also, scrap the stock head bolts for metric ARP head bolts - the stock bolts are TTY and are junk/non-reusable for a rebuild.

Change the pistons, rings, and call Raylar for springs and rockers, maybe even valves if you need them. Have a nice short block done and have the heads done correctly. You cant swap parts with other big blocks - they are a different generation. The 496/8.1 may as well be Ford or Chrysler - its not the same. The only thing you can get from Summit is the pistons and a timing chain IF ITS A 496/8.1 spec - other parts have to be stock or Raylar.

If you use the truck block understand that the marine block is all metric, the truck block has SAE threads for the bolts on the bellhousing and some of the mounts are SAE - not metric so the install gets a little confusing.

Yes I see what you are staying about rocker arms I was planning on sourcing everything g thru raylar just for ease of purchase. I am not out to cheap out for a buck like I said earlier I am here to make a solid engine that will run worry free for a while. So nothing needs to be done to my ecm for installing the rocker arms?

Good choice sourcing parts from Larry @ Raylar. Sounds like you will have a stout reliable setup. No changes needed to the PCM swapping to Raylar's roller rockers. Factory ratio is 1.7 .