Gear Ratio and Distributor differences..Cobra, ,Merc

Stan's Customs · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Roger that Don S... ...these boats are already propped out correctly in their present form. Unless I change the hp a lot, I can speculate a little. Plus I am curious about the Mercruiser. The OMC takes a lot deeper prop,a 17, than any Mercruiser I have owned in a similar size boat. Just wondered if the gear ratio was substantially different. Thanks ..Stan

Lou C · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Well Stan I have my 1988 OMC shop manual in front of me, and it looks to me like the trim system is isolated from the ign circuit, the power goes from the batt term on the starter solenoid to the up and down relays, then to the trim motor. The relays are switched on from the tilt trim switch. The only thing I can imagine is the tilt motor is drawing so much current that it drops the batt voltage momentarily when it first kicks on. Can you check the charging voltage at the batt (digital volt meter) with the motor running, then hit the trim swith to see how much it drops? That might lead back to all the connections in that circuit, bat terminals, cables, starter solenoid terminal, and the terminals on the relays. Salt water can do weird things, but I have not had this happen on mine (yet!)

seahorse5 · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

A common problem with a voltage drop when the trim button is pressed is a corroded ground stud and terminals on the rear of the engine. Remove the stud and re-tap the threads in the block, wire brush the stud where it is corroded, and sand the ground wire terminals until they are shiny. Replace the rusted nut and lockwasher with stainless steel hardware.

rodbolt · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

hello you still aint getting it. most mercs now use the starter lug to tap the trim. OMC used it as well. the difference between using the starter lug and the battery post is a few feet of cable and a few terminals. Bondos spark theory is entertaining but has nothing to do with marine flame and ignition proofing. while an arc will travel in a stright line normally, it can cruise around a corner, if the dielectric properties are comprimised, it can go around a corner. the problem is the vapors can and do go about corners and voids. the ionized gasses are also a part of it. we used to drill holes in the caps on race cars to help eliminate missfires due to ionazation. the shielding wil help quench a spark as well as a flame but also prevent the buildup of an explosive fuel mix. if its vented, it cant go boom. on the shift interrupt the OMC used a spark scattering device that looks almost like an outboard power pack.the called it ESA. it was desined to scatter the spark and cause a misfire while holding the engine RPM at about 450 RPM. most early versions used a cut out switch to ground the system and an over stroke switch to unground it once in gear. the switches were hooked in series. merc just killed the ignition and hoped the switch would release before the engine quit rotating. while the ability to jury rig is admirable, lord knows I have done it and still can if the need arises, dont jury rig enclosed machinery that has the potential to build explosive vapors until you are familiar with why they made it that way. when I was young and full of energy I grew up in my dads wrecking yard. I was 8 years old and had access to anything in the yard. I was also 8 when dad gave me my first chiltons manual and 13 when I got my first penske inductive timing light. I still have it and it still works. so jury rigging and adapting were a way of life growing up in the lower part of alabama in the 60's. I am a master at it. however I also read. I read a lot. there are many books on the subject. one is the ABYC manual. get a copy and read it. dont try to always outsmart the engineer try to figgure out why it was done the way it was done. some times I think it was done cause someones brother in law sold widjets

. I am not trying to bust your chops. I am trying to make you think about your package and how all the subsystems work to make a high performance machine. its amazing how a bad battery cable or cable end can take a 16,000 dollar motor and make it run nasty. always rember 2 points point one is this aint voodoo nor black magic. point two is everything has to work within a physical set of paremeters no matter who or where it was built. its all about the basics parts is parts I take all them tiny parts and make a big part. if all them tiny ones are happy so is the big one

Don S · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Originally posted by Stan's Customs: The trim should be totally isolated from the ignition circuit. Whatever the reason, isolating the trim from the system with a relay or solenoid and a direct battery hook up (with a big fuse) would seem to be an easy fix... can't understand why they wouldn't take that precaution in the first place. It will be that way if it isn't, soon.

Ya know Stan, they did take that precaution in the first place. If you look at the wiring diagram you would see it......do you have one? I'm really beginning to doubt it. You are also trying to over analyze everything, you really need to go look and check some things before attempting to do even more analyzing from the previous answers. You also mentioned you were never allowed to use the word can't, well maybe you can do some of this stuff, but doing it safer, to work better, and cheaper than the "Real" parts is another thing. Just like the distributor sealing. You don't think the Coast Guard and the other marine safety teams didn't do research to figure out what worked and what didn't???? How many people visiting this site have also done the same amount of testing to see what works and what doesn't.....of course there isn't. It's time to get your hands dirty my friend....... check out your trim problem, pull some engines and drives and see what fits where. It can't all be done on paper and the computer.

rodbolt · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Stan we aint ragging on ya. DonS, seahorse and a few others are proffesionals at this. we have todo it right or bad things may happen. Louc is on the right track but you will not find a momentary loss or spike with most digital meters. the meter circuits are not that quick. what we are trying do do is make you solve the problem by pointing you in the direction ya need togo. if one of us were looking at it over your shoulder we could most likly find theproblem in a few minutes. howeverthe internet is not that advanced yet and I aint so sure I could do it when it is

. hang in there with us and keep posting. you seem mechanically inclined now we have to make you technically inclined

but if you dont belive me about the trim motor looking like an electrical short do a resistance test between the green and blue wires if you have a 2 wire motor. between the green and black and blue and black if you have a 3 wire motor

Stan's Customs · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

I may have given you the wrong impression, Rodbolt... Jury riggin' is never a consideration here, and as you said this ain't voodo or magic. I just needed to know exactly what a marine distributor consisted of...I asked the questions because I wanted to see if it was something I could duplicate using an HEI, and of course I can. It was "never" my intention to circumvent any safety precautions, merely to duplicate them if need be. Now...thanks to help from you and others I have more information to work with on this marine problem. Ain't computers grand, just like a talking repair manual...if you get the right tech....I read a lot too. I also started with my Dad's old Motor's Manuals...which I too still have, as well as many of his old antiquated hand tools. Jury rigging.. Come to think or it, If that means some way other than was done on these boats 15-20 years ago, yep I might be a jury rigger....providing I can do it better. So was Don Garlits.. There's lots of silly designed old equipment equipment in the world today, this may not be any of it, but that's why I'm asking the questions. Knowledge and experience is the answer .... If jury rigging means doing something stupid or ignorant that could injure my Grandchildren or other loved ones...by by passing safety issues in a hot enclosed fume intense engine compartment, then ..well you know the answer to that by now. Like I mentioned in an earlier post somewhere, I don't pretend to be a Marine mechanic....No apologies there, I'm good at what I do and when I get thru with this project I'll just be better and more knowledgable concerning Marine work.... When I'm through with this, it all may dead stock...That depends on whether dead stock is the best way to do it, or not. For what it's worth, I'm pretty sure I'll use the marine distributor....based in no small part on information you have provided. The other issues have yet to be resolved....hopefully they will be as simple as you suggest..and don't think that I take your advice lightly.(also Seahorse and LouC) My whole business is inovation based...most of what we build is one of a kind...So I have a habit of looking at all angles before I get in deep. Don't take it personally, it's just how I've survived all these years. I'm not trying to bust your chops either...and I really do appreciate your help. Thanks for the shift information..since I'm changing the drive to a mercruiser from OMC, the boat has a OMC interrupter already on it. Do you perfer it over the Mercruiser..or would you change the whole setup? Thanks and best regards...Stan M

rodbolt · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

hello again no chops busted here but you will never get an HEI to work for long periods of time reliably in a marine application. the delco EST seems to hold up for a few years before sucummbing. the delco EST is very similar to the HEI but with an external coil and no there is no dist cap to housing gasket. as far as which system is best it will depend on what ign system you go with. if you do try to use the HEI dont wire it so it shorts the BATT lead to ground, if the switch sticks a bit it will pop fuses and melt wires. however I can modify the harness on the OMC to use the merc style system. you will have to rewire the amphenol connetor for the esa and scrap the ESA. its not hard, just have to understand what the shift interrupter is and does and what the overstroke is and does. otherwise you will be in a mess

.

Stan's Customs · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

You're right Don... Time to get my hands dirty.. The weather has been crappy and the boat is down by the lake. When I can get it in my shop for a while it's next on the agenda. We just don't have the extra room for a couple of weeks. I didn't have enough time before the cold front came in. There really is no short cut...I'll have the manual open when I start on it..unlike now. Thanks for the kind words Rod...I'll take all the tutoring I can get... Stan

Stan's Customs · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

OK ...the HEI is out. I'll can buy a distributor... or use the OMC distributor which has the Pertronoix ignitor, or the old '79 point type Mercruiser distributor. Since I'm mix matching some here. What would be the most desireable combination, if cost wasn't a particular factor, including the preferable shift interrupter, and engine controller. The doner drive and other parts are from a'79 model 260 mercruiser. The project boat is a 1988 Cobra 5.7. Stan Suggestions??

Winger Ed. · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Originally posted by Stan's Customs: "you can get anything you want, at Alice's Restaurant"

As I recall, "You can get anything you want at Alice's Restaraunt,,,,,,, except Alice".

Bondo · Dec 5, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Bondos spark theory is entertaining but has nothing to do with marine flame and ignition proofing.

Really rodbolt................... Just Exactly Where do I go from Fact, to Entertainment ?????

Since I'm mix matching some here.

You Should be using Either the Merc. OR the OMC...... Not Both, Or Pieces Of Both.........

Lou C · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

I wondered what modifications you would have to make to the wiring harness in the OMC boat for the Merc shift interrupt--since they do work a little differently. If you are thinking of keeping the OMC I would consider going back to the OE style points distributor just to eliminate the electronic system as a possible trouble source. If you have the seal leak fixed on the Cobra drive, why not just run it as long as you can, they really are not that bad, you can get all the outdrive parts anyway, and nothing has an easier to replace impeller! The main issue with them is finding someone who knows how to adjust the shift linkage and make sure the ESA system works, other than that they are fine. I am going to run mine as long as I can get parts, when I can't I am going to do the Volvo SX conversion, you change the pivot housing to the Volvo style, add the engine mounted impeller, and Volvo shift cables, and a modification has to be made to the trim rams. Still that sounds like an easier job than converting the whole think over to a Merc (since you keep the OMC transom shield, rear engine mount, tilt n trim, and power steering).

Stan's Customs · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

You remember exactly right ..Winger Ed.. At least that's what the song said.....now I remember an Alice..........ha. Hey Lou.. Kinda depends on what shape the OMC saltwater drive is in internally. I could go ahead and use it for a while...I was just thinking since I have to rebuild the motor anyway.....I'm already half way there... The Volvo conversion may be easier but I already have the Mercruiser parts. Guess I could sell that stuff and ............ Hmmm.. on the other hand, I guess I could sell all three boats put a grand with it, and buy one that needs nothing...of course I've seen one of those, Ha.. Hey Bondo...I was considering using all of which either one I used, at least topside (interrupter, distributor, and engine control)...not necessarily matching the lower unit though. Bad idea ? Still wonder which system is preferable....or if it makes much difference...? Thanks....Stan

Lou C · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Usually salt water damage in an engine is harder to evaluate that in/on the drive, since you can see more of the drive damage. If there is a problem what you will see is pitting and deterioration of the aluminum. I have seen it and it is most often seen in slipped boats in a "hot" marina. Usually you don't get clogging of the cooling passages in the drive. Now the motor is another story, since cast iron flakes off when it corrodes, and eventually you will find clogged risers, and overheating due to the build up of deposits. So if the drive looks good, shifts good and needs a re-seal, I would use it as long as the power package is reliable. That motor that has blow by, have you done a compression test to see if in fact the rings are bad? If you left the 20' OMC, and fixed the motor, then you could keep the Merc powered 84 intact and potentially have the use of either boat as long as you don't mind fixing stuff.

Bondo · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

I was considering using all of which either one I used, at least topside (interrupter, distributor, and engine control)...not necessarily matching the lower unit though. Bad idea ?

Ayuh............ 1 or the Other......... I can't even Imagine How that Idea could Ever Float.......... About the Only Mixing & Matching like That, Would be the Basic Long Engine Block............. I'm not saying it Can't be done.... But, You'd end up with a Real Cluster ****....................

rodbolt · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

what bondo syas . I have a 1974 wellcraft airslot 24 that came in today that is so jury rigged and cobbled I just closed the hood and wrote, to many safty defects and improper jury rigging to repair. he has a choice now. a repower or take it down the street

if you use the cobra transom/drive you have to use the shift plate and linkage from the OMC. if you use the Merc drive you have to use the merc stuff. the long blocks may or may not I think the 84 used a two piece crank seal and the 88 used a one piece. the flywheels and sometimes the couplers changed. if both motors have 4 bolts down the center of the valve cover they may both have one piece rear main seals. if one has 4 bolts on the periphery of the valve cover odds are good that it has a two piece seal.

Stan's Customs · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Hey Lou Well, the drive has some pitting on the outside...but it has been repainted as if to clean it up before selling. Doesn't look "plum terrible" now.. but there are pitted areas all over it. It would have been easier to evaluate had it not been painted. I bought it sight unseen..with a guarantee that it would run and shift good. The carb was messed up and the ignitor plate in the distributor was improperly installed, a dual problem, that acted like one(the carb). Just crapped out when getting up in the rpm's so I decided to take it anyway.....it was cheap. Fixed the carb and the distributor ...runs smooth and shifts good.. The blow by was moderate till it got hot...then it's as bad as it gets. But it's a Chevy and I 've got engine parts out the wazoo...have a son-in-law workin' in a Chevrolet parts dept and am good friends with the department manager. Parts arn't an issue.....plus we do a lot of engine work here. The salt issue really didn't sink in until I winterized the boat....bought it in north Texas. I was just piddling with this thing when I had a few minutes here and there. When I winterized the lower unit and pulled the plugs on the top sides of the lower unit...nothing came out....when I investigated with a light, is when I found that the port side was completely plugged with salt. Later when I drained the manifolds...big chunks of metal were in the big drain plug caps on the bottom of the manifolds....Then the light began to come on.... Well duh....salt water boat. Let me back up a little. Earlier I noticed that a thermostat was laying in the side rail...I kinda thought that it may have been taken out when winterized last season, but no. So I installed a 160 degree right before we took it to test the last time...If the gauge is right it's running about 190, maybe a little more. The inside of the thermostat housing was corroded badly where the thermostat goes....took a few minutes to get it scraped out enough get the o-ring and stat to seat. Bad weather prevented installing a test gauge to see if the OMC gauge is accurate so.... Now back to the rust chunks when winterizing...they may be restricting the manifold and block passages and the engine running warmer because of it...Had to stop there so I don't know yet. 190 degrees won't hurt it just seems high for a 160 degree thermostat with a chill in the air after 20 minutes run time. As far as the engine goes ...I'm going to replace or rebuild ...depends on the water passages when I tear it down...unless somebody tells me these salt exposed blocks don't rebuild well...Never touched anything exposed to salt..haven't a clue what to expect. Like Don said I need to get my hands dirty...and get further into the problem....never enough time for the toys, busy, busy. The engine expense is acceptable..the boat is worth it.....now past that is debatable. If the salt damage is such that I had to spend a lot on the drive too...I'd probably bail out. Here is where I started investigating the possibility of using the old Mercruiser stuff I already had...which happily is a "can do" so I'll stil be OK on the money if I had to go that route. Now the rest of the story... The reason I bought yet another boat, the '84 Mercruiser, is really a just in case thing..."Because"....Our family has a "big" reunion planned Memorial weekend at Possum Kingdom lake in north Texas. I have promised all the kids I'd have a good ski/pleasure boat there for them if they would come.....they are all excited, the reservations are made and the party's on....so, I bought a little insurance! One way or another there will be a boat there. Who knows, I might get lucky and have 2 boats for them to play with . We've got a big family anyway... That's the rest of the story and how all this got started in the first place ... Now if I just had some spare time... Stan

Stan's Customs · Dec 6, 2004

Re: Gear Ratio and Distributor differences..Cobra, ,Merc

Hello again Bondo, Rodbolt... I didn't know if the shift linkage was similar or not. Clearly it isn't...not a problem I have all of both. There may be problem with the flywheels that I won't know how to address until I tear them down to be sure, unless one of you knows... Rod, you are right about about the 1 piece and 2 piece main seals. The 88 OMC is the newer one piece rear seal....If I change the outdrive I will use a '79 Mercruiser drive , the flywheel and coupler came off an old style engine naturally..... I don't know whether there is a flywheel that will work on the new style engine and the old style drive, do you? I believe the crank shaft bolt pattern is different. So I may have to use an older engine for the rebuild....if I transplant the old '79 Mercruiser drive, etc. That's not a problem I have a good older engine ...but the later model has better heads, and it might be machined for the stock roller cam. That is right about when they started the roller cams, I think. Providing my mine isn't rusted up to bad to I'd rather use the later block. Stan

Gear Ratio and Distributor differences..Cobra, ,Merc

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