Hey Vinney - Reversition?

[coupedeville]

I, and perhaps a number of others would just love it if vinney would please explain what a static line is, what reversition is, and just exactly why a roller cam will cause water to be sucked into your engine through the exhaust. <br />

 

[vinney]

Re: Hey Vinney - Reversition?

That is exactly the problem understanding of whats going on. Volvo and Mercruiser have many service bullitins on this problem. I didnt make this up I work on marine water cooled engines. It sound like to me you dont understand what a cam shaft can do in a water cooled exhaust. If you like information I will be glad to share my knowledge but if you think you already have the answers I will pass. If you dont know what the static line is you better school up or you will be buying engines. Maybe no you personaly but the owner of the company. I cover my tail and try to be on the top of the curve of knowledge not the bottom. As for the term water reversition volvo Penta came up with that. We use to call it water injestion but the new term is water reversition. Im an engineer by trade and own a boat business not because I have to but because I want to. I look at the boat business from an engineering point of view first then attack it mechanical piont of view. Static line I didnt make that up either Mercruiser did. If you read the service manuals cover to cover its in there.I have read every book I can get my hands on (the boat business)cover to cover. I make it my business to know whats going on that why im in the boat business.

 

[snapperbait]

Re: Hey Vinney - Reversition?

I'll try to explain why a roller or any other cam with certain specs, for that matter could pull in water...<br /><br />Without getting into camshaft specs, some camshafts are made so that the intake and exhaust valve overlap and briefly open at the same time.... This allows the exhaust for a very short time to pull in vaccum just like the intake valve, thus the slight possibility of pulling in some water... I think that's what he means by "Reversion"...<br /><br />As for "static line", I have not a clue either..

 

[vinney]

Re: Hey Vinney - Reversition?

THe old days prior to roller cam the manufacture (mercruiser) spec the cam when the engine was marinized. When the roller cam engine came out there were no after market roller cams so we used what was avalable. The new roller cam engine makes alot more power than the flat tappet cam engine. The cid is the same. The manufacture makes the power with the roller camshaft and the new cylinder head design. There is a positive pull on the exhaust when the engine is on the compression stroke. The engine want air in the cylinder when its going on the compression stroke it doesnt care if its the intake valve or exhaust valve. The new roller cam engine has a much larger pull on the exhaust. Why do you think there are rises on engines. I didnt make this stuff up I make it my business to know whats going on. Static line that something you better have a handle on or it will bit you.

 

[vinney]

Re: Hey Vinney - Reversition?

Before the roller cam there were no extentions for risers. Now there 3 inch and 6 inch. Volvo redesigned there risers and make pulse tubes for there risers. Mercruiser makes a resonator for the exhaust. There are exhaust flappers that go in the exhaust hose 4 inch after the riser in the dry side. Volvo has changed there installition guide to there engines. I didnt make this stuff up I pay attention to detail.

 

[Bondo]

Re: Hey Vinney - Reversition?

The Static line vinny refers to is the vertical relationship between the point(riser) where the exhaust water turns the corner from being pumped Up, to Falling down, And the water level outside the boat..... the water HAS to be able to Fall down the exhaust pipe...and higher is better....<br /><br />Reversion, when the throttle is hauled back, there is Alot of vacuum in the motor.... this vacuum carries all the way to the exhaust manifolds......It can,+ Will suck water back into the cyl.s if a cam with an LSA(Lobe Separation Angle) of over 112* is used... marine cams have LSAs of 109* to 112*......<br /><br />Vinny's dislike for roller cams Probably stems from people using aftermarket roller cams, which tend to be Too Big for their application(reversion,+LSA again)..... Many people think "if it makes 400hp in a dragster, it'll be great in my boat"....<br />the OEM roller cams seem to be working out quite nicely....<br /><br />Hell, I understood Perfectly...!!

 

[snapperbait]

Re: Hey Vinney - Reversition?

Thanks Guys....

 

[coupedeville]

Re: Hey Vinney - Reversition?

Yo, vinney; I never said you were making this stuff up. And if I knew the answer, I wouldn't be asking.<br />Seeing as you're an engineer, and also in the boat business, I thought maybe you could offer up a short summary on these subjects. That way I won't have to read service manuals cover to cover. <br />I am familiar with overlap in a camshaft - I don't think I've ever seen a cam that didn't have overlap. Some more than others, of course. Long duration cams, such as you'd find in a racing engine have loads of overlap.

 

[vinney]

Re: Hey Vinney - Reversition?

Static line The way to determine true static line is to get a 1 inch clear hose about 12 feet long. Put one end over the boat and in the water. then take the other end put some water in it. Take the end that is not in the water make a loop in it with water in the loop. Lower the loop below the engine and keep the end above the engine. So you have a loop with water in it and the end above the engine the level in the hose is the true water line. You make a mark on the engine usally on the exhaust manifold then measure up to the top of the riser this distance is the static line. Static line for a Flat tappet cam shafts was 8 and 3/4 inches. The new roller cam requires 13 and 3/4 inches of static line so that the engine will not ingest water in thru the exhaust at idle. You can take and engine and run it out of a boat with out water to it and put your hand over the exhaust at the riser and feel the positive pull on the exhaust at idle. If there is water present within that 13 and 3/4 it will be pulled into the engine thru the exhaust side. We have made an example to show customers an engine with clear exhaust hose and put water in the hose and you can watch the water being pulled into the engine. If you are milking up the valve covers the water is being pulled in thru the exhaust up the exhaust valve and in to the valve cover. static line if the boats seen the cylinder heads of prematurely check static line.

 

[vinney]

Re: Hey Vinney - Reversition?

Coup its not YO its SIR

 

[SS MAYFLOAT]

Re: Hey Vinney - Reversition?

Thanks Coupedeville for bringing this up. It has helped shed the light for me on understanding on how water can be brought back into the engine. So if you have your boat loaded to its limit and then some, this would lower the static water line which could destroy your engine? Is this true? If so, I now know why my one buddy is having problems with water in the oil. (even after changing complete engines/manifolds) This did happen after he redneck engineered two gas tanks in the back of his boat. DUH.... Then with his full load of kids and their friends...NO DOUBT!<br /><br />Glad to have all of you here on the board, you are an asset to this forum! <br /><br />You learn something everyday!

 

[vinney]

Re: Hey Vinney - Reversition?

Static line is the silent killer of marine water cooled engines. It gets misdiagnoses more that any other problem. If you dont get it correct you will be buying engines at first the manufacture will buy you a set and then they yell uncle. Then you end up paying. Cylinder heads didnt come of engines at the rate they do to day. Heads came of engines when they needed a valve job because of carbon on the seam or a burnt valve. Today we remove heads all the time because the seats are all rusted up and the stems are tight in the guides. This is signs of water coming in thru the exhaust valves. If the static line is close and you weigh down the boat you will have a problem. Gas, gear, people, diving equipment, the list can go on. The biggest problem I see is the boat is being delived from the manufacture with static line issues. Then the chase is on. Is it the boat manufactures problem? or the engine manufactures problem? and we as a servicing dealer want to fix the boat for the customer and there is no room to move the static line up in the boat.

 

[ODDD1]

Re: Hey Vinney - Reversition?

Yeah, Vinney..trying to fix it after its been built that way always stinks......learned along time ago what a servicing tech needs in a boat is [if your lucky] an afterthought.....boats are built to be sold, PERIOD....anything that can be cost cut, lightened, crammed together for interior space increases will happen, as long as most of the boats make the warratee period....companies live or die by sales, and techs dont buy many boats........

 

[geriksen]

Re: Hey Vinney - Reversition?

We have seen problems with this on 25 top 28 foot single engine cruisers. Not so much reversion but water ingestion while the boat is sitting still. On a narrow beam cruiser with a deep hull the engine sits very low indeed. On our lake there is a "party cove" the boats all tie together and have a huge party. When they do these boats fill up with people so much that we have had engines fill up with water just sitting there. If there is room for riser extentions they usually fix the problem. We have had two Scarab 29's sink because they were so full of people that the vents went under. There is a picture going around on the internet of one of them. I was right there when it went down. <br />P.S. Yo, Vinney, lighten up Sir........... You have made some valid points but we can all learn here. I have been repairing boats professionally for eighteen years, but I still do not profess to know it all. There is always something I haven't seen yet that someone else has, and vice versa.

 

[vinney]

Re: Hey Vinney - Reversition?

Thank for the help.

 

[jlshields]

Re: Hey Vinney - Reversition?

Vinney and all others, will the overlap on these roller cams cause the vacuum gauge needle to 'vibrate' between 13 & 14 inches on a '97 5.7LX B3 in a Monterey 256 Cruiser without risers, just elbows right on the manifold? I had engine trouble, #5 piston scuffed, cylinder scored, wrist pin knocking, rings stuck, and ex. valve seat cracked. Machine guy said looked like detonation. After reading several threads about it I'm wondering if I suffered reversion. Opinions appreciated, John

 

[MrBill]

Re: Hey Vinney - Reversition?

A note about roller cams...from my drag racing days. It is not the roller cam per se that may cause what has been referred to as "reversition". It is solely the specifications of the shaft itself, more specifically the shape of the cam lobes. Most modern cams have intake-exhaust overlap to some degree, and this is not specific to roller cams. Roller cams do, however, permit more radical configurations, such as higher lift and longer (valve open)"duration".<br /><br />To accomplish the more radicial configurations, the so-called "roller cam" is used, otherwise excessive wear would result on lifters and other components of the valve train. On an ordinary camshaft (looking at it horizontally) the tops of the lobes are canted or slightly beveled so that when it comes in contact with the lifter, the lifter spins so that it doesn't wear in only one spot and get "cupped". The lifter rods should also spin when the engine is running. Failure to do so indicates wear, stickiness or improper adjustment.<br /><br />Roller cams use a different type of mechanism that I won't get into in depth. But, to be short, in most configurations, roller equipped lifters ride over the cam lobes and eliminate the striking which normally takes place when the cam 'pushes' or strikes the lifter. Roller cams therefore must have flat topped lobes rather than the traditional canted or beveled tops. The two types of cams are not interchangeable, TRUST ME...<br /><br />I'll be able to comment additionally, later, sorry I'm out of time.

 

[jlshields]

Re: Hey Vinney - Reversition?

MrBill, I'm familiar with the mechanics, my question is 'Will the overlap cause a vacuum gauge to 'vibrate' at idle rather than read steady'? It does this after overhaul. It reads steady as a rock on my 300M. Thanks John

 

[MrBill]

Re: Hey Vinney - Reversition?

Assuming engine is stock....you should not see the oscillation that you describe as a result of a roller cam. "Vibration" or oscillation at idle indicates wear in a component of the valve train. In the range (13-14) that you described, I would suspect a leaky valve or worn valve guides. If the range is larger, say 13 to 16 and rather slow, you could really luck out and potentially correct with adjustment in idle fuel/air mixture.<br /><br />The faster movement you described, combined with the "detonation" issue however, leads me to believe that you could have a burnt and/or warped valve.

 

[coupedeville]

Re: Hey Vinney - Reversition?

Thank you Bill for describing the difference between roller and flat tappet cams. Saved me a lot of typing! You can have a 2 cams with identical specs: The valves open and close at the same time and with the same lift and with the same profile, except one is designed to be used with roller lifters, the other with flat bottom ones. Roller units are steel, aren't they? As opposed to iron.<br />A knew another old gearhead would come to the rescue!