305 to 350 build questions

[Rick Stephens]

I hear ya. Well, it isn't all that hard to pull a motor out again if it needs it. Only hard part for me is you are already there, ready to tank and bore. A set of pistons, rings, bearings gaskets and pretty good shape for a long haul. But I still hear ya.

 

[Scott Danforth]

Mic the bores, my guess the bores are out of round.

 

[jimmbo]

If it's burning oil, it probably needs new bearings and probably a crank

 

[Scott Danforth]

needs to be pulled apart and inspected.

rings and valve seals are the first two culprits.

crank and main bearing bores need to be mic'd along with the bores.

if it needs a rebuild, a new rotating assembly would be my choice.

 

[gr8shot]

Mic the bores, my guess the bores are out of round.

Based on what in the pictures? None of the cylinder walls looked too bad. It was a good running motor when it was pulled. Shouldn't there be spots where there is tons of harsh wear if the cylinders are out of round?

I totally understand your logic of do everything possible to it while the motor is torn down. But here's my thoughts. This isn't my only boat, it's a cheap project boat. My main boat runs great and is perfectly usable although smaller and older than this one. My thoughts are, based on this being a great running motor when it was pulled, put it together and drop it in the boat and see how it goes. If it runs great and needs nothing, I'm that much money ahead. If it ends up burning oil, low oil pressure, water in oil, etc. Well, I still have my normal boat for us to use, and I can pull this motor back out, spend the money on the motor at that time and still be out on the lake all summer long in our current boat.

 

[scoflaw]

No way that motor runs "great" with plugs that look like that.

 

[AKJohne]

It was gorgeous out on Saturdays so I got the heads off the "new to me" motor. Things look pretty good to my untrained eyes. Didn't see any cracks between the valves on the heads. Didn't see any abnormal wear in the cylinder walls. Some strange buildup on the plugs and intake valves in a couple cylinders. See pics. I'm thinking this engine may have just had bad intake gaskets, not a blown head gasket. I couldn't see any evidence of a leak path anywhere on either head. But it didn't come with an intake or the intake gaskets so very likely it was an intake gasket leaking coolant into the oil, not a head gasket. I'm going to see if the one local machine shop can get the heads in and gone through anytime soon. And then the fun starts, ordering parts!

Would have been a good time to do a leak down test.... before it came apart....

 

[Lou C]

I'm going to have to agree I see signs of deferred maintenance. Looks like the oil was rarely if ever changed and there is heavy carbon build up/coking in the cyl heads. For the amount of money it would take to have it gone through, as long as the heads are not cracked and can be re-done, and then you re-do the lower end, you are starting with something good and not have to go back and pull the engine again. I'd get some quotes and see what you're dealing with money wise.

 

[gr8shot]

Well update time. Heads are at the machine shop getting checked out. From the initial look he thought they'd be just fine, but obviously he's going to check for cracks, replace seals and do all the normal stuff.

My lazy butt finally bought an engine stand so I could check out the short block. Unfortunately I wasn't as lucky as I'd hoped. Some of the bearings had pretty normal wear. #6 rod bearing had a bit more than I'd say is normal. And the #1 main bearing was trashed. Crank looks fine, just a light polish I think should take care of it. But as of now, I've got the short block completely stripped down and hoping to take it to the machine shop tomorrow after work. There's some weird almost rusty looking spots on a couple cylinder walls. But no deep gouges or grooves in any of them, nothing I can feel with a fingernail in the cylinder walls or on the crank. So hopefully a good hone will be all the block needs and I can reuse the stock pistons. Enjoy some photos of what I found, in no particular order.

 

[alldodge]

Looks rebuildable, but don't see honing, I would think bore

 

[gr8shot]

I also started on the boat side of things last night. Got the drive removed at least. Tonight I'll start working on getting the 305 ready to remove. I kind of lucked out on one major aspect. I was really stressing over how I was going to be able to lift the 305 out, and the 350 into the boat. It's obviously too tall for a regular engine hoist. Well as kind of a side hobby, I buy, repair and flip diesel pickups occasionally. I happened to get a STEAL on this truck in December. So after a bit of work, it runs perfectly, and all the stuff in the back now works perfectly (crane, welder, and air compressor). So I have got a 3200 pound crane at my disposal that will work awesome for lifting and removing engines from a boat. And as a plus, when I sell this truck, the profit will more than pay for the purchase price of the boat, all the money I have spent on the engine, maintenance, cover and accessories, plus more. So all around win-win!

 

[Scott Danforth]

you need to measure the bores with a bore gauge looking for taper and out-of-round.

I have never ever ever come across a motor you could simply run a dingleberry in it and drop the pistons back in and get it to run right.. especially one that has bad bearings.

i would plan on a line-bore to clean up the mains (or you will suffer another bearing failure), a .005 deck to true up the block, and at a minimum, .030 over the current pistons

 

[gr8shot]

you need to measure the bores with a bore gauge looking for taper and out-of-round.

I have never ever ever come across a motor you could simply run a dingleberry in it and drop the pistons back in and get it to run right.. especially one that has bad bearings.

i would plan on a line-bore to clean up the mains (or you will suffer another bearing failure), a .005 deck to true up the block, and at a minimum, .030 over the current pistons

Machine shop is going to check all that out for me. I don't have any of the tools to measure any of that kind of stuff. I'll just do what they recommend and go from there.

 

[gr8shot]

Another update. Boat engine is out now! Everything was surprisingly straight forward, and came out pretty nicely. The crane on the service truck was an absolute life saver! Not sure how I would have gotten it out otherwise. Engine is mounted on an engine stand for teardown once I get the 350 block back from the machine shop and assembled.

Heads are finished at the machine shop, but I left them there since they'll be in a climate controlled environment versus my unheated shop. Glad I took them in, he said they were in pretty bad shape. He basically replaced everything on them, which hurt my wallet pretty bad. But they're essentially brand new heads now. He said the block should be done next week. I'll have to order bearings, rings, maybe pistons if I can't reuse the stock ones, and a few other odds and ends, then can move on to assembly!

Oh and for giggles, I looked up the casting number of this boat engine. Comes back as "2 bolt, Vortec truck, roller cam, one piece rear main seal". So there's that for future use in case anyone tries to argue that marine engines have special blocks.

 

[Scott Danforth]

if you spent more than $800, new heads would have been cheaper.

no, there is nothing special about marine blocks....... they come off the same assembly line as trucks and trash pumps and natural gas motors used in power generation with the exception of Mercury Racing motors which are purpose built by Mercury Racing (including the 502 which starts off as a pile of parts from GMPP)

get coated bearings if your wallet allows.

 

[gr8shot]

if you spent more than $800, new heads would have been cheaper.

Thankfully it wasn't quite that expensive but close enough. Although a buddy messaged me literally the same day I paid the bill for the heads asking if I wanted to buy a set of aluminum heads he had (don't remember what they were, but I know they were good ones) for less than $100 difference from what I paid the machine shop.

I ended up with about a $650 bill for the heads. New seals, guides, valves, springs, and all the associated machine work to make them like new. I told him I was just doing a stock rebuild, and trying to keep costs down, so not sure why he decided to just go ahead and replace everything. But too late now.

 

[Scott Danforth]

hope you at a minimum clearanced the guide towers for the smaller seals needed for clearance for a decent cam and switched to thread-in rocker studs

 

[gr8shot]

hope you at a minimum clearanced the guide towers for the smaller seals needed for clearance for a decent cam and switched to thread-in rocker studs

I honestly don't know. I left them at the machine shop so they'd stay in a climate controlled room vs my un-heated shop. I don't think he clearanced anything for a bigger cam. Which is ok, I'm sticking with the stock mercruiser cam unless I find it's not in good enough shape from the 305 when I tear it down.

 

[gr8shot]

Looks like it's go time here tonight! FINALLY got my block back from the machine shop. He told me less than two weeks, and it was over 5 weeks. I believe I've got all the parts I need to at least get the bottom end put together. Bearings, rings, gaskets, plastigauge, assembly lube etc.

I tore the cracked 305 down a little bit yesterday and got the cam out. The cam looks like brand new. Can't even see any wear marks on it or anything. So I'm going to run it in the new 350. I talked myself out of buying a bigger cam on account of really not needing that much more power in such a small boat. The 305 was cracked very slightly in the lifter valley, and huge chunks blown out on the outside.

I'll try and snap some pics as I work on things tonight.

 

[Scott Danforth]

make sure to keep the lifters matched to the lobes