1975 Mercruiser 888

[Brandon5778]

Hello iBoats crew, I guess it's time to officially make a thread because I need help. I have a 1975 Cobalt I/O powered by a 302 Ford engine. This is a new-to-me last year boat. I have done quite a bit to the boat already and when I put it away I thought it was ready for next year (engine-wise). It would stay cool and was running good. Well I took her out on Friday (I can honestly also say I've never been on the lake in February) and first off she would not stay cool, even just at idle. I had to shut it off when the needle got to the red. It also seemed like it was running like garbage (hard to start, seemed like a loss of power when I got on the throttle). So I thought why not do another compression test and see what happens. I thought all was pretty good until I got to the last cylinder. There was 0 compression. It would jump up on the gauge when I bumped the starter but in a fraction of a second it went back down to zero. I am pretty sure I winterized it right, nothin' but air as you guys say. There was 6 drain plugs that got drained, I raised and lowered the tongue of the boat a bunch of times to get any trapped water out, and I put a paperclip into the drain plug holes to clear debris.

So here I am. Feeling kind of depressed about this happening after everything I've put into it.. :grumpy: I know it's time to pull the heads and inspect. The thing is, I am 19 years old without any prior experience with rebuilding an engine. So I apologize right now if anything you say goes above my head. I'm really good at learning and it doesn't seem that hard to pull apart, but like I said it would all be new to me. I guess my first question is really where to begin, and do I need to pull the drive and engine first? This might be kind of difficult for me but I do have access to a backhoe to be able to pull it out. My boss told me, though, that I could pull the heads to have a look right in the boat. I just want to know what you guys think I should do, because I don't have a clue..:facepalm:

Thank you all for your valuable time.

Here's some pics of the boat.

 

[Bondo]

and first off she would not stay cool, even just at idle. I had to shut it off when the needle got to the red.

Ayuh,.... Start by replacin' the impeller in the drive, 'n back-flushin' from the t-stat housin', while the lower unit is off,....

There was 0 compression. It would jump up on the gauge when I bumped the starter but in a fraction of a second it went back down to zero.

That sounds like a bad test gauge, more so than a bad cylinder,...

 

[Brandon5778]

Hey bondo, thanks for the reply. I forgot to mention somehow in the original post that we replaced the impeller and water pump housing last fall when we got it started and the temp kept rising. The old one was still in one piece. We also replaced a crusty old thermostat and that made the temp stay cool. I'm relieved you think it sounds like a bad test gauge. I was using a loaner from a local auto parts store, should I get a different one and try it again?

 

[Bt Doctur]

As far as running hot, how old are the manifolds and risers.

 

[Brandon5778]

I have no idea, original as far as I know. Boat was run in freshwater, and had 300 hours when I purchased.

 

[Brandon5778]

That sounds like a bad test gauge, more so than a bad cylinder,...

Bondo thank goodness you were right. I got a different compression tester and these were my results.

120 115 120 115
115 110 120 115

However I just fired her up and of course still it started getting hot. So I need to figure out what test to do to find whatever is wrong. I am assuming as of now it is probably my manifolds and risers. I just don't know how to tell. Why would it be able to hold a temp just 3 months ago the last time I had it in the water, but not now??

 

[Bondo]

we replaced the impeller and water pump housing last fall when we got it started and the temp kept rising.
However I just fired her up and of course still it started getting hot.

Ayuh,... Sounds like ya screwed up the impeller swap,....

Pull the lower unit, 'n Look,....

 

[Brandon5778]

Ayuh,... Sounds like ya screwed up the impeller swap,....

Pull the lower unit, 'n Look,....

Sorry, I didn't realize I worded that so confusingly, when we first got it started last year the temp kept rising, so then we did the impeller & thermostat, and after that the temp held steady. I took it out a couple times. Now this year it is getting hot. I am very confident we put in the impeller right. We even had to go back and replace it again because I accidentally ran it dry because the old spigot I was using turned the water off and I didn't realize it for a minute.

 

[Bt Doctur]

Try shifting into fwd, remove the drive, insert hose into water inlet and test run. If the hose remains in the housing then manifolds and risers may be good, if hose pops out with pressure or will not stay in the inlet you have a restriction in the circulating system and may be clogged risers.
If temp is better, then start at the drive. Sometimes depending on the amount of scale released by leaving a motor dry
it may plug up the risers at the first start up .

 

[wrench 3]

In your description of winterizing you didn't mention pulling off the large hose on the water circulating pump. If you didn't remove and drain it, the circulating pump may be damaged.

 

[Brandon5778]

In your description of winterizing you didn't mention pulling off the large hose on the water circulating pump. If you didn't remove and drain it, the circulating pump may be damaged.

I didn't remove the hose. How likely it's damaged?

 

[wrench 3]

If the hose wasn't drained water would remain in the bottom of the pump. So it depends on how cold it got and how lucky you are.
If you remove the pump there's no back cover, so it's easy to inspect. Check the impeller for distortion and any sign that it was hitting anything. Make sure that it's tight on the shaft. Also inspect the pump housing and the timing cover for cracks.

A thought on your running problem. If no one's converted it, it will have ignition points. They usually need cleaning in the spring.

 

[Brandon5778]

Alright, so here's kind of a semi-update.

College and work has been demanding too much of my time to get anything done on the boat. I'm taking 18 credit hours and should be graduating this semester.. What I have done is pulled off the circulating water pump to check for freeze damage, as indicated in this thread. It's pretty crusty, but the impeller seems to be all around ok, no visible cracks anywhere I can see, and it is "tight on the shaft". I am going to put it back on the engine as I think it is okay. (after I find the right gasket). Here's pics of the pump.

So, I have been thinking, and I think I have a plan of attack.
1. I bought a new impeller for good measure, and I'm going to change it out. I was thinking about it long and hard, and I remembered that I only recently learned that you cannot rev the engine up over like 1200 RPMs while running on the muffs + garden hose. Yeah, I'm learning all kinds of new stuff. I think I'm guilty of doing just that after the new impeller was put in. So I will shift to fwd, drop the lower unit, and as Bondo states back flush while the drive is off from t-stat housing. By this I assume to just take off the housing, and pour (or do I want pressure and to use the hose?) water in from a jug. Then I will swap impeller and put it back together. I remember having trouble getting my lower to go back up the last 3 inches or so last time I did this. Can anyone recommend any tips for putting the lower unit back on?

2. If it still gets hot, then I plan on removing the drive, and as BT Doctur recommends, I will insert the garden hose into the water inlet and try running it to see if it pops out.

3. Also, while I was at my boat, I tried to take off the port side riser just to visually inspect it. I took off the 4 bolts, but I could not get it off for the life of me. I tried spraying it with penetrating oil, and I was using a rubber mallet to try to knock it loose. No go. This thing is stuck. Is there something I'm missing? I ended up just putting the bolts back on and leaving it. I took the hose off the riser and took a picture of that opening too, it was looking very crusty.

4. And finally, it was time to finally start looking into the cost of new risers and manifolds. I think I said somewhere, I got a feeling that I will be buying new ones. After looking into it, I could only find one brand, aftermarket ones made by Sierra. And they are not cheap. $320 a piece for the manifolds, and $120 for the risers. A total of $880 dollars with free Prime shipping.. Does this sound about right? I guess I'm finally seeing the price of having a Ford based Mercruiser. Bust out another thousand, lol. :faint2:

 

[Bondo]

By this I assume to just take off the housing, and pour (or do I want pressure and to use the hose?) water in from a jug.

Naw,... Just pull the in-comin' hose off the t-stat housin', 'n stuff yer garden hose into it to back-flush it,...

and I was using a rubber mallet to try to knock it loose. No go.

Try thumpin' it with a block of wood,... it's rusted on there,...

Btw,... That exhaust don't look that bad at all,...

 

[Brandon5778]

Thanks Bondo, as always, so grateful for your help.

Btw,... That exhaust don't look that bad at all,...

I will take that as hopeful thinking!

 

[wrench 3]

Water pump looks good too.

 

[Brandon5778]

Any advice for lining up the lower unit when I put it back on? I had a heck of a time getting the last 2 inches the first time I did it.

 

[Bondo]

Ayuh,.... I wrap a bungee strap from the cav-plate, 'round the prop, back to the other side of the cav-plate,....

Turn the prop shaft, while shiftin' the shift spool to Forward, 'n 1 more click, to hold tension against the clutch dogs, in forward gear,...
No chance of it slippin' into neutral, 'n ruinin' the effort,...

Start the drive shaft, then the water tube, then the shift shaft,...
The last 3/4" could be spline bind, so turn the prop shaft slightly for it to fall into place,...

'n don't forget the big silver washer that sits on top of the shift spool,....

 

[Tim in TN]

Cobalt? I had a 1976 Mark Twain 180T with the exact same hull design. Looks very similar inside too. It too had the Mercruiser 888 power plant. Loved that boat, just had to spend so much time working on it instead of riding in it.

 

[Brandon5778]

Ok, so tonight I put in the new impeller. This was the first time doing it completely all on my own, and I still had trouble getting the last inch back together. I had the lower unit slip into neutral, and at first I didn't understand how to get it back in forward. But persistence is key and I got it all back together. Thanks Bondo for the help with that. I certainly learned something, and committed the process better to memory. Hopefully next time I have to do it won't take near as long.

Here's a pic of the teardown and my makeshift bucket lower unit stand

Unfortunately, I don't think the impeller is my problem. Here's pictures of the one I took out that I suspected might have been damaged from revving engine up too high on the muffs. It looks pretty good, no signs of damage to me. I put a new one in it anyway. I haven't ran it yet because I still don't have the gasket to put the water pump back on the engine. Hoping to pick one up tomorrow. That also reminds me, does anyone know where I could get the little o-ring that fits in the bottom gear lube drain screw? I lost it tonight. I'm hoping iboats has it..