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Old 09-05-2014, 06:24   #1
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Mumblings from Someone about to Rebuild a Cylinder Head - Advice?

Hello,

I've got myself a new (used) lovely little sailboat, a Bandholm 24, with a small 13hp Renault (RC16D) engine lurking in the bilge, from 1985. I've had it for about 3 months now. When I first did the delivery sail, we motored for about 10 hours with no issues. Since I've owned it, it's always emitted a small amount of blue smoke, but starts up PERFECTLY every time, with no glowplugs (doesn't even have them) in about 8C weather. After the 10hour sail, only a very small amount of oil was consumed, noting too troubling.

After the delivery sail, I replaced the oil & filter with new and have been using it very sporadically. Since the oil change, I ran aground on some sand (embarrassing, but no damage) but I was able to get her free with some serious revving of the engine in reverse. Since then, I've noticed a gradual "greying" of the oil (definitely not "diesel black" any more) which indicates to me some obvious water intrusion into the oil. The engine also tends to puke out a pretty embarrassing amount of oil through the cooling water, very obvious blue sheen on the water behind me.

So, I've decided to replace the head gasket. The parts are next to impossible to find but I've been able to source one for 160Ä. I'm quite sure that after my overloading the engine, I've caused the head gasket to fail. I can also see some oil seeping between the head and the block in some places. I've got the repair manual and a torque wrench so I'm quite sure I won't **** this up. Due to the raw water cooling being in very cold water, I'm 99% sure that this engine has never been overheated. It's always just "warm" to the touch.
While I've got the head off, I want to replace the valve guides, and grind the valves. The engine does not have valve guide seals. My reason is because I think they are leaking oil into the intake/exhaust manifold, through the guides. When I turn the engine over by hand, I can hear a hissing emitting from the intake manifold. I believe this is because enough crap has built up ontop of the valve and is preventing a perfect seal, and there is definitely not perfect compression (I can turn the engine over by hand if I do it slowly enough, about 4 seconds per cylinder) But because the engine starts perfectly, i'm lead to believe that the fast compression of the piston forces the valve closed, and the engine can start normally (as it always does.) and therefore the leak is hopefully not past the piston rings. The exhaust manifold has obvious traces of oil if I jam my finger down it, but it has very little carbon build up.

Just wondering if anyone has any thoughts or tips, or if anyone with more experience things my reasoning is totally off. The engine is cosmetically in very good shape, with the original paint covering most bolts. I really doubt this engine has been a "mechanic's special" and has just "worked" for all those years, but maybe asking 30 years from a head gasket is too much.

Thanks for the help! I would love to hear any comments!
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Old 09-05-2014, 09:53   #2
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Re: Mumblings from someone about to rebuild a cylinder head - advice?

Seems like the head gasket must really be leaking to blow rocker arm return oil into the cooling system. It may have nothing to do with the cylinder seal though. Then I suppose a water passage near the oil drain passage(s), could be leaking. Your oil leaks on the exterior are a good sign that you are on the right track. Not sure why running the engine hard for a few moments would blow a head gasket. It was probably about to go anyway. mumble- mumble...
You probably know they can knurl the valve guides to bring them back to size and as to seals they are easily added or not. Some engines don't use seals on the exhaust just the intake. I think you would be wasting a big effort not to have the valves ground, guides replaced/knurled, head surface checked and maybe put fancy little Teflon seals on the intakes.
I sure hope the inside of the cooling system is not so corroded from the salt water that it is not the cause.. What a primitive way of doing things.
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Old 09-05-2014, 10:56   #3
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Re: Mumblings from someone about to rebuild a cylinder head - advice?

Only the intake valve stems need replacing/ knurling. The exhaust stem only sees pressure and not vacuum so no oil is pulled through the guide.

As the engine starts up fine, compression and valve seats should be fine. If the valve was leaking it would be a bear to start. But while the head is off its easy to lap the seats.

BTW an easy way to break the seal between the head and engine, is after the valve train and head bolts are removed, crank the engine for a 1/2 second. The compression will break the cylinder head free easy pezy.
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Old 09-05-2014, 16:10   #4
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Re: Mumblings from someone about to rebuild a cylinder head - advice?

[QUOTE=sailorchic34;1537085]Only the intake valve stems need replacing/ knurling. The exhaust stem only sees pressure and not vacuum so no oil is pulled through the guide.

What are you talking about? If a valve is going to go bad it's most likely an exhaust valve. The heat and lack of oil wears out the valve guide, seat and valve. As for lapping a worn valve seat and valve that went out with the Model A. There are several angles that need to be cut on a valve and seat and lapping will only work for the last little bit, if at all.
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Old 09-05-2014, 16:44   #5
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Re: Mumblings from Someone about to Rebuild a Cylinder Head - Advice?

Doesnt mention if its fresh or saltwater cooled.If fresh the first thing I would do is do a leakdown test on the cooling system. I sometimes just lap valves to check how the valve is seating and freshen it up. If its worn so part isnt lapping or looking silver in a nice even pattern its time to grind and start looking at valve depth and the possibility of needing new seats and or valves. If your there check all the specs, gnurling and stem and or umbrella seals would be prudent if nothing is beyond service limits.
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Old 09-05-2014, 18:40   #6
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Re: Mumblings from someone about to rebuild a cylinder head - advice?

Quote:
Originally Posted by Guy View Post
What are you talking about? If a valve is going to go bad it's most likely an exhaust valve. The heat and lack of oil wears out the valve guide, seat and valve. As for lapping a worn valve seat and valve that went out with the Model A. There are several angles that need to be cut on a valve and seat and lapping will only work for the last little bit, if at all.
Oh sorry I was only talking about Knurling the inside of the valve stems, which is done on worn valve stems to reduce oil consumption through the stem. You only really do that in the intake stems as the exhaust stem only sees exhaust pressure and not vacuum as the intake does.

Hey I'm an old fashion girl and have lapped a valve or two in my day. But yes if the valve or seat is leaking then grinding and valve and or seat may be required.

While many new engines do have two angle valve seats, most of the older engines still have that old fashion single angle seat.

On a little two cylinder raw water cooled engine that starts easy, a leaky exhaust valve is probably not a problem. The OP has a blown head gasket which is which is not uncommon and yes maybe worn valve guides. Myself I might just pull the valves and lap them if not appreciable wear and have new valve stems installed or Knurl the intake stems.
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Old 09-05-2014, 19:19   #7
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Re: Mumblings from Someone about to Rebuild a Cylinder Head - Advice?

I"ve done up many engines with a quick fix of lapping in valves, checking valve guides, getting a pressure check done, skimming surface flat. The head is already off, pull out the pistons, check cyl for wear, check cleareance in big end bearings, replace rings. Assemble. Rigged myself up to machine the cyl head and pressure check or take it to a shop. Over 20 years I only had a couple of engines requiring full overhaul. Corrosion may be your biggest problem as the cooling water is not treated.
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Old 09-05-2014, 21:03   #8
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pirate Re: Mumblings from Someone about to Rebuild a Cylinder Head - Advice?

$220 bucks for a head gasket?
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Old 10-05-2014, 18:04   #9
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Re: Mumblings from Someone about to Rebuild a Cylinder Head - Advice?

Leaking oil cooler tube? Might pay to check before taking off the head.
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