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Old 12-10-2014, 10:59   #16
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Re: Badly overheated Volvo MD6A....now no compression??

Perplexing! On the positive side it doesn't sound like a ring problem. If that was the case it probably wouldn't have quit. It would have been sucking sump oil, making black smoke and been damn near impossible to shut down.
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Old 12-10-2014, 17:07   #17
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Re: Badly overheated Volvo MD6A....now no compression??

Come to think of it........a couple of years ago I made a trip of about 5 hours where the engine ran pretty hot. Bad day all around. Wife got real seasick and I just wanted to get her in. Anyway, the next day the engine would not start. I got a mechanic, we bled the engine, he looked at the valves, could find no reason.

So he just cranked the dickens out of her, WOT, until she cranked. I've nebr had the problem before or since. The engine always starts very easily, except that one time.
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Old 12-10-2014, 18:01   #18
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Re: Badly overheated Volvo MD6A....now no compression??

Thank you all for the suggestions. Today I cleaned and inspected the parts I had already taken off Friday (before posting):

-Intake mesh 'filter' and breather filter - very oily.
-Exhaust manifold - corrosion, deposits and rust chunks in water passages as expected. Minor carbon deposits. Carefully opened clogged water passages with Dremel then blew them out with my power washer and compressed air.
-Head - valves move fine and are all closed. Lifters and rockers look fine. Head is surprisingly flat against steel straightedge (couldn't get feeler gauge underneath). The three external head studs had seriously frozen nuts however so the studs unscrewed rather than the nuts. I heated and removed the nuts thinking perhaps they hadn't allowed that side of the head to seat quite enough.
-exhaust elbow - no evidence of blockage.
-thermostat - garbage.
-gaskets - Head and exhaust gaskets showed no obvious signs of failure.

I've started to wonder about sticking rings as a cause for the compression loss since the motor has just been idled periodically for a few seasons but I will get a good tester and do a proper pressure check and fuel system check upon reassembly.

Cheechako - it is RWC and your point is really good - it could be something else. There's no discernable cylinder ridge.

Jeffjd - it did seem just slightly more resistant when I got toward TDC but it still seemed about as easy to turn as my 6hp push mower - not what I'd have expected for even a small high compression motor. Wish I'd rotated it my hand before for comparison! !

Arthur - a winter tear down certainly may be in the cards and repairing all gauges is a high priority. I'm also going to look into rigging up fresh water cooling.

I have unlimited SeaTow so may sail the boat to City Island then have SeaTow take it the rest of the way. In the interest of yankee ingenuity/wasting time I'll try putting the head back on without machining since it looks visually good to see what happens. Getting it professionally towed even if it does restart is starting to seem prudent..hate the idea of my first transit to be on a tow line but GREATLY prefer that to having my first transit end at the bottom of the Gate!!
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Old 12-10-2014, 18:14   #19
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Re: Badly overheated Volvo MD6A....now no compression??

Cadence - I appreciate that. I may try a bit of marvel mystery oil on the Pistons before buttoning it back up since it's all exposed, but I'd sure like the rings to be good and unstuck!

Grant - great points about the barrel brushes and the thermostat requirement. I'm searching various catalogs to see if there's an interchange 140-degree F replacement that doesn't cost $110...but I'll not run without one!

Compass790 - that is a great tip. I work in engineering also so have been researching different ways of reusing that gasket if possible...at least to move it out into the channel to head closer to its new home before towing.

I'm also going to give the engine an oil change. It is still full after the four hours I did put on the motor since purchase...and it strikes me as a bit thin...which concerns me about fuel blowby.
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Old 12-10-2014, 18:20   #20
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Re: Badly overheated Volvo MD6A....now no compression??

About the fresh water kit. My MD7A has a Sendor (spelling?) fresh water cooling kit on it, and the passages are very clean. The only thing I dont like about the fresh water cooling, is that it uses the hand crank position (end of cam) to put the pulley for the extra pump. If I ever had a complete electrical failure, I could remove the fresh water system and revert to sea water fairly easy, so that I could use the hand crank, but would need to carry a 140 degree thermostat and gaskets, to replace the much higher temperature fresh water thermostat. What a difference between the water passages in the fresh water cooled MD7, and the spare salt water cooled MD6 that I have. I hope it all works out for you. ______Grant.
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Old 14-10-2014, 23:24   #21
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Re: Badly overheated Volvo MD6A....now no compression??

I was on another forum tonight, and a Volvo owner said he was able to get a thermostat from Napa Auto. He took the old one in and matched it for size and temp. $25 rather than Volvos $75. I also ran across the web site the fresh water cooling kits. Martec International, Sweden, and the MD6/7 kit is number 901-1011. The whole site was in Swedish, so I dont know what the prices were. The one on my engine is SENDURE, but I dont know much about it. ______Grant.
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Old 15-10-2014, 10:26   #22
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Re: Badly overheated Volvo MD6A....now no compression??

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Originally Posted by Sur la Mer View Post
Cadence - I appreciate that. I may try a bit of marvel mystery oil on the Pistons before buttoning it back up since it's all exposed, but I'd sure like the rings to be good and unstuck!

Grant - great points about the barrel brushes and the thermostat requirement. I'm searching various catalogs to see if there's an interchange 140-degree F replacement that doesn't cost $110...but I'll not run without one!

Compass790 - that is a great tip. I work in engineering also so have been researching different ways of reusing that gasket if possible...at least to move it out into the channel to head closer to its new home before towing.

I'm also going to give the engine an oil change. It is still full after the four hours I did put on the motor since purchase...and it strikes me as a bit thin...which concerns me about fuel blowby.
Marvel Mystery Oil can't hurt a thing. I believe you had said kero was used on the valves? I'd try the Mystery oil on the valve stems. To me, since you said exhaust/steam I'm assuming white smoke which could just be a sticky valve and unburnt fuel?
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Old 15-10-2014, 10:50   #23
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Re: Badly overheated Volvo MD6A....now no compression??

A hurry and a deadline to transit the East River....
Unless you have two weeks off, I'd suggest trying to beg, borrow, or steal a large outboard engine and plan to make the trip that way.

You can wind up digging an expensive hole by rushing an engine rebuild, and then if it fails anyway, you can also wind up digging another expensive hole trying to sail in the East River. It IS possible to transit the East River under sail, but depending on timing and what else is making the trip at the same time, it can be a challenge.

What Grant mentions about the thermostat? Raw water cooling on a boat is usually set up differently from the thermostat in a closed system like your car. In a car, the thermostat just blocks or permits water flow in one hose. In a raw water installation on a boat, the thermostat shunts the water through a "T" fitting. As it heats up it blocks off the "dump" side and forces the water into the "engine" side, so in order to run without a thermostat, you need something to BLOCK OFF the normal "dump" flow, and force it through the engine instead. A nice stable rock, properly chosen for size, can actually do. Its also fun to watch a professional open the thermostat housing, remove a rock, and hear him ask "I really don't want to know, do I?"
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Old 18-10-2014, 10:18   #24
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Re: Badly overheated Volvo MD6A....now no compression??

Update on this: yesterday I left 1/2" of Marvel in both cylinders and today it's gone...into the crankcase. I'm hopeful I am seeing stuck rings and not broken rings. The cylinders have some carbon at the top but no ridging...in fact there's nothing I would consider significant if it was a gas motor. Maybe the higher compression is more sensitive to light scuffs? I'm going to reassemble, change the oil and try to start it. A compression check is obviously going to be a waste of time at this point. I have some Seafoam here. Any final suggestions?
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Old 18-10-2014, 10:31   #25
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Re: Badly overheated Volvo MD6A....now no compression??

Sounds like you should pull those pistons if you've gone this far. how much can rings be? Even if you just do a quick overhaul by honing the cylinders and new rings might be worth it. When you said the mechanic started it by cranking fast a lot... sounds like low compression to me. Have the head checked, grind the valves new rings.... might go for a long time...
In the "old days" people used to overhaul car motors that way a lot. Did a few myself...
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Old 18-10-2014, 10:45   #26
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Re: Badly overheated Volvo MD6A....now no compression??

IIRC if you pull the pistons on a Volvo, you must also order new bolts for the connecting rods. Not "should" but "must" because these parts will deform during installation and cannot be retorqued properly. A friend of mine tried to shave down a rebuild (on an MD6A or 7A, I forget) by asking the shop to reuse those bolts, and a year later, he needed another rebuild as one of the old bolts failed.

FWIW, sometimes it pays to not take things apart unless they definitely will need to be apart. Especially with Volvo parts, hand crafted by artisan metalworkers in the far north.(G)
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Old 18-10-2014, 10:49   #27
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Re: Badly overheated Volvo MD6A....now no compression??

Yeah... there are some things on older Volvo's that are not readily apparent. Something about "shimming" also... have to buy factory shim set...? Anyone remember what that is about? or is that the MD2B etc type only?
However... this engine is mostly apart now I think... hate to see him put it back together and have the same issues...
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Old 19-10-2014, 17:34   #28
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Re: Badly overheated Volvo MD6A....now no compression??

Quote:
Originally Posted by Sur la Mer View Post
Update on this: yesterday I left 1/2" of Marvel in both cylinders and today it's gone...into the crankcase. I'm hopeful I am seeing stuck rings and not broken rings. The cylinders have some carbon at the top but no ridging...in fact there's nothing I would consider significant if it was a gas motor. Maybe the higher compression is more sensitive to light scuffs? I'm going to reassemble, change the oil and try to start it. A compression check is obviously going to be a waste of time at this point. I have some Seafoam here. Any final suggestions?
Educate me please...what do you surmise from the fact that the Marvel was gone? In fact, why did you use the Marvel in the first place? What does it do?
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Old 19-10-2014, 17:55   #29
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Re: Badly overheated Volvo MD6A....now no compression??

hpeer-
Sounds like an old-fashioned leakdown test. You fill each cylinder, typically with kero or diesel, and let it sit overnight. If the rings are tight, the fluid is still in there come morning. If the fluid has leaked down past the rings, the engine needs a ring job.

These days compressed air is often used. Assuming you have a compressor, the head is still on, and you have the adapter to screw into glow/spark plug threads in the head.
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Old 20-10-2014, 11:32   #30
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Re: Badly overheated Volvo MD6A....now no compression??

After cleaning out the Marvel and removing some carbon from the very top of the cylinders I found one small spot where seizure had occurred one one cylinder. The other leaked down slower but did it did leak and had a bit of scuffing near the top (hard to see). Since I was there and had nothing to lose (key gaskets carefully reused/sealed, secondary gaskets 'made' with RTV) I went ahead and reassembled the motor then tried to start it. Under continuous cranking it spit a few times. I can feel better compression when turning the flywheel by hand, but clearly it's not enough so the motor needs rings. (Hpeer - I originally hoped the rings were only stuck and that the Marvel would free them up). Since that rebuild'll be a long term project I'll order proper gaskets with the rings and rod bolts (Thanks hellosailor. What are these shims of which you speak, Cheeechako?) If I find better than list pricing I'll post the source for the group...and I'll start another thread for rebuild Q&A.

As for my upciming boat move I've started tuning my old 15hp Evinrude long shaft, purchased a motor mount, and made sure my cell phone and VHF are set to Seatow's contact info.

Thanks to all who reponded!
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