MR-1 crank, no start, bad compression

[Jgorm]

I had some if this piled in another thread, but it's time to focus on major issues. Here is the history.
Test drive 2004 ar230, runs great, started up multiple times, no hesitation at wot, 10k+ rpm at wot. Decide against doing a compression test. Engines look super clean, no rust, no pits at all on the zinc, probably never been in salt.

Come back the next weekend and buy the boat (200 miles away). Take it to the river. Starts fine, runs great. Day two at the launch ramp I can't get the port engine started. I jiggle the lanyard, cycle the clean out switches, with no luck. I pull the air filter and it starts, put it back on and it won't start. Take it off and it runs great all day. I forgot to blow the water out, so I try to start it the next day and it struggles but I eventually get it running.

I discover the key switch has the yellow / red wire broken and think, easy fix. More testing shows that that wire doesn't do anything, and it starts multiple times over the next couple days.

Pull the plugs and they look fine, a little rich maybe on a couple, but pretty good. Run compression with the lanyard off, throttle button in, wot until max reading.
1 = 195, 195
2 = 100, 100, 100w, 100w
3 = 165, 165
4 = 205, 205

Seems to be valve related. What's the cost to take it in vs diy? Any chance an oil change and some hard driving might loosen thing up? (Yeah LONG shot, but I've "fixed" a transmission like that!) Could I eek out a season in this condition, or will I end up with total destruction?

I'm pretty mechanical, been dyno / email tuning efi Ford's since 2005 as a side business, installed superchargers, intake manifold replacements, brakes, axles, lift kits, etc, but I've never had the heads off anything yet.

This is not what I was hoping for with a new boat! Check compression before you buy anything! I'm kicking myself for not spending a couple hours doing a more thorough check.

 

[Gym]

That's a bummer @Jgorm. I'm wondering if the previous owner knew about this before he sold it. If he had a Yamaha dealer near him you could call them to see if they looked this boat over before you bought it.

If you are sure it's a stuck valve pulling the head would be easier and cheaper than pulling the engine. You could either do the repair yourself or bring/send the head out for repair. Make sure you get a repair manual for the correct specs.

 

[smashedheadcat]

Get yourself a service manual and it should walk you through it. I haven't touched a Yamaha, but I've been through this process before (ironically enough) on a 4v ford engine (I tune my own 03 cobra) Basically, turn the crankshaft to the "safe space" and start in bolting things.

However, before you dig in, pick up a leakdown tester. That'll help you identify where the air is escaping from.

 

[Cobra Jet Steering LLC]

Just curious as to what makes you think it is valve related usually two low readings in the center of the engine are head gasket or warped head, etc. check with @fairpilot he had something similar due to corrosion

 

[Jgorm]

Just curious as to what makes you think it is valve related usually two low readings in the center of the engine are head gasket or warped head, etc. check with @fairpilot he had something similar due to corrosion

Totally possible. I was not aware that gasket failure is more common than valve issues on these engines.

 

[Jgorm]

However, before you dig in, pick up a leakdown tester. That'll help you identify where the air is escaping from.

I have a leak down tester, but saw no point to bother when the heads gotta come off.

I got the yds finally. The starboard had no codes, but the port had a low oil, and overheat code, but they were a long time ago. 400hrs. I had the service manual printed and spiral bound. ($50) it doesn't seem too difficult.

 

[itsdgm]

@Jgorm sorry to hear about your issues. I'm still in the middle of repairing a boat with a stuck valve issue. I'm becoming an expert at pulling a Yamaha engine though . Pm me if you need any tips/pics. Btw, what area are you in? I'd be willing to help if your close.

 

[Jgorm]

I finally had some time to dig into it. Milkshake oil that is difficult to see on the dip stick. I recommend bringing a suction device to sample oil when buying a boat. I believe the po changed the oil prior to my purchase. Oh well lesson learned. I need to figure out how to rotate the engine so I can get it to tdc and remove the cams.

 

[Bruce]

Could you rotate the impeller to get the engine to TDC?

 

[tdonoughue]

Isn't there a hex fitting on the shaft coming out of the back of the engine, just forward of the bearing? If I remember correctly, it may be a matter of removing the plugs, putting a long rod in #1, and rotating until max altitude on #1, right?

 

[cybuch]

@Jgorm , I wonder if you are having the same issue as I am with a crack. Do you have water in the oil?

 

[Jgorm]

@Jgorm , I wonder if you are having the same issue as I am with a crack. Do you have water in the oil?

I hope not! Did you have bad compression on 2 + 3? Yeah, I had a nice milkshake.

 

[cybuch]

Bad compression on 2 and milkshake, but ran perfect!

 

[Jgorm]

I made some progress today. Looks like no crack! Here are some tips if you do this.

1 take off intake throttle body assembly. It comes off pretty easily as one assembly.

2 take off exhaust by removing the 4 large bolts on the long pipe going aft. Buy some hose clamp pliers because they kick ass! Loosen the clamps on the 90° elbow. Slide it towards the headers to get to the two hose clamps under it. Loosen only the one near the long pipe. Shift the long pipe away from the assembly. Undo the bolts that connect the two headers into one. There are a bunch of them! See images. Tilt that assembly aft and jiggle to get the locator pins free.
3. Then take the valve cover off. I'm here for now. I'll post more as I go.

 

[cybuch]

@Jgorm Thats good news, no external cracks. I will tell you, mine started as internal and worked their way external. I hope your issue is something simple!

 

[Jetti]

Why could you not pull the valve cover/exhaust and hose down the stuck valve with penetrating oil and give it a light malatizing with a rubber hammer to free it. Malatizing is aloud on aircraft engines, works 90 percent of the time.

 

[cybuch]

Did I miss something, is it a stuck valve?

 

[Jetti]

If there is no water in the oil, and it had been sitting for awhile the residual water in the exhaust corroded the valve stem and seat. If you catch it early penetrating oil will free the stuck valve. I use aero kroil it in an orange can, and frees alot of stuff. I hope this helps.

 

[cybuch]

He said oil looks like chocolate milk, would have to say that is water.

 

[Jetti]

I would still check the valves before complete teardown. If the exhaust valve is stuck slightly open (low compression) on the intake stroke the water in the exhaust will be sucked in and will mix with oil. I had it happen on my old baja. If you can turn engine over slowly and feel for movement of the low compression cylinder exhaust valve. Just to count that out. Or the head gasket is fried.