Gear Ratio and Distributor differences..Cobra, ,Merc

[Stan's Customs]

Good morning all....<br /><br />Can abyone tell me what the difference in gear ratios (if any ) is between a 1984 Mercruiser 898 w/ 5.0 and a 1988 Cobra w/5.7. <br /><br />The Cobra requires a considerably lower prop than the Merc..thought there might be a contributing factor other than weight, even though there is some weight difference.<br /><br />Also of the two boats I've been working on...both have had some loss of of fire problems. One has an after market electronic module and one has the Merc Thunderbolt ignition. <br /><br />Hence the question...can a GM HEI distributor be used on these v/8 drives without causing a fire hazard or something? Looks like waterproofing the cap and connections is all that you'd have to do... Unless these marine distributors have something else going for them I haven't noticed. I know I can end the reliability problems I'm having with the GM HEI and I have several good used ones.<br /><br />If the above is not an insurmountable issue..then what about the spark interruptor. ...How is it wired to the ignition. <br /><br />Thanks and have a good day...Stan

 

[Don S]

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

If it's not a marine distributor, don't use it in a boat.<br />Another problem with using a GM HEI distributor is the advance is all wrong.<br />Best thing to do on the Merc TB ignition is repair the problem.<br /><br />

 

[Stan's Customs]

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

Thanks once again Don for the reply.....<br /><br />I want something I can easily repair..Seems like some boat ignition systems cut out with the trim activated..and all kind of screwy problems that no one has any answer for... other than a bad ground or a new alternator. I guarantee an HEI won't be affected like that. <br /><br />Many of the older boats even have points..if they haven't been converted with after market kits. Nothing special about those..Mallory distributors were what I cut my teeth on.<br /><br /> I wasn't suggesting using a distributor without taking every precaution to make it safe.. I was talking about improving the ignition and making it better in any way possible..parts availability...diagnosis ease..and most important, reliability. I never break down next to a boat dealer, especially one that stocks any parts. <br /><br />What I need to know is some specifics that make the marine distributors supposedly safer than anything else. I can duplicate "anything" they do with an HEI, especially the advance curve...and water proofing, insulation etc. Which is all I see different...unless, like I mentioned, I have overlooked something... If I have... please tell me what it is, so I can fix this problem, quickly and economically..(which is seldom possible with marine specific parts, it takes forever to get them and they are usually high $$$).<br /><br />The Coast Guard labels are a warning for those that might not be aware of the potential danger...which of course excludes ninety percent of the members that participate in this forum....and especially professional mechanics. <br /><br />I can assure you my standards far exceed anything the Coast Guard might require.<br /><br />Having said that...do you have any specific information that would help an automotive mechanic of 30+ years. <br /><br />I don't pretend to know much at all about Marine repair ..but since I have paid my dues in the automotive field, maybe I can bridge the gap with some marine specific information. <br /><br />Mostly respectfully yours...Stan M.

 

[JasonB]

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

Have you considered a Pertronix kit?<br /><br />BTW: the 898 liklely has a gr of 1.5:1

 

[Stan's Customs]

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

HI Jason....<br /><br />As a matter of fact the OMC has a Pertronics kit that had the mount plate installed incorrectly. It will mount in 2 positions. I fixed that when I finally figured it out, but still have a little miss when the trim is bumped...<br /><br />That's one of the problems I believe an HEI would eliminate....<br /><br /><br />Maybe not though, who knows when it comes to little gliches like that.<br /><br /><br />Stan

 

[tommays]

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

stan<br />one thing you cant do is put a CG aproved lable on it which will save your bacon should there every be any type of accident on the boat<br /><br /> they are not a warning they are a legal requirement as the parts are as different as something that does the same thing could be<br /><br />But to be more specific marine distributors have a spark screen similar to marine alternators that allow them to safely vent any fire that could result from fumes. It works much like a flame arrestor on the carb any backfire is released safely instead of igniting fumes that may be present<br /><br />Rather than think they can seal something electric on land or sea in a enclosed fume area both NEC and CG regs both go with Murphy’s law and try to have each part be able to safely deal with any fumes and also not turn into a hand grenade or spread the fire<br /><br />The best way I could relate it would be spray booth safety like trying to make your own EXP proof motor<br /><br />Figure 1-23. Design criteria for constructing explosion-proof enclosures.<br />184 Electrical Safety in Flammable Gas/Vapor Laden Atmospheres <br />As a result of these requirements, an explosion-proof enclosure that is <br />designed for a particular group may not be capable of withstanding the explosion <br />pressure of another group. For example, suppose an explosion-proof enclosure <br />designed for Group D will be used for a Group B atmosphere. The maximum <br />explosion pressure that can occur in a Group D enclosure is from gasoline which <br />can develop 160 lbs psi. The enclosures for Group D must withstand 4 × 160 = 640 <br />lbs psi. If the B atmosphere should contain hydrogen, the enclosure is subject to an <br />explosion pressure of 845 lbs psi when the hydrogen entering the enclosure would <br />be ignited. The enclosure, then functioning as a hand grenade, could do considerable <br />damage. <br /><br />thats a small land based sample of the many rules that go into building a legal part<br /><br /><br />tommays

 

[rodbolt]

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

hello<br /> think man think.<br /> your miss problem when the trim is bumped. study the system and you tell me.<br />with the hei the problem will likly be worse.<br /> the HEI was never approved for marine use. your quote"Unless these marine distributors have something else going for them I haven't noticed."<br /> look a bunch harder<br /> the HEI had a bad habit of rusting away the advance weights its even worse when you place it in a wet engine box. I have seen it done many times but always with more trouble than its worth. for not much money the TB ign was good the delco marine EST is good. I never had a problem with points, but if you dont fix your electrical system any distributor you install will be problematic.<br /> good luck and re eyeball them marine distributors and post back what ya see

 

[Stan's Customs]

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

Thank you Tom , Rodbolt...<br /><br />I haven't seen the screen you mentioned on either of these boat's distributors. I will look closer ....may not be there.<br /><br /> I have seen rust as you mention Rod..a non issue, easy to prevent. I have had better luck with the old marine point distributors than these I have now. <br /><br />You guys are probably right...I'm just aggrivated that something this simple seems to be a recurring problem . If I can power heavy winches on my rigs and the engines not cut out...a trim motor shouldn't be a problem..or anything else a boat has for that matter. I can't fault the electronic system everything looks and works good...Poor design is the main problem in my view.<br /><br /> We have built complete wiring harnesses here before Painless Wiring was a dream....I can straighten up this cheap harness if I must. Which ever of these boats I build will have some major upgrades.<br /><br />Arrggg..me heartys, blowin off steam. The whole boat isn't worth me gettin aggrivated about, or worse aggrivating the posters that try to wade thru this stuff and be helpful. You guys are great and really appreciated. I'm sure I'll wind up using stock Marine equipment... Please forgive my ranting....I'm sure I'll work it out eventually.<br /><br />How about the gear ratio question..anybody ??<br /><br />How about the outdrive interchangability...any body?? Don S remembers the 1988 Cobra and 260 Mercruisers (1979) cutout being the same...OOps that's the other post. Anyway does anyone have some template information?<br /><br />Thank you all once again...Stan

 

[Lou C]

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

Stan there was an OMC service bulletin on the motor cutting out from the trim switch, do a search you may be able to find it, Seahorse posted something about it on here. If you can find a Johnson/Evinrude dealer that used to sell Cobra stern drives, they may be able to look it up for you. Has to do with the resistance wire and coil I think. Mine has never done it up to now anyway.

 

[Don S]

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

Wrong thread.

 

[Winger Ed.]

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

Originally posted by Stan's Customs:<br /> ..can a GM HEI distributor be used on these v/8 drives without causing a fire hazard or something?

Alot of marine distributors look exactly like their 'car' counterparts. And, except for the advance curves, they may well be just a auto dist. put in a boat engine.<br /><br />But, 'boat' dist. caps always have a 'O' ring around their bases. That, and their limited production compared to their auto. counterparts, drives the price up.<br /><br />That 'O' ring keeps the fire in, and the moisture out..... Which also makes it 'Coast Guard Approved' <br /><br /><br />If ya gotta, gotta use a HEI ign. system, you might get the marine weights & springs, and a marine cap, or at least run a bead of silicone around the bottom of the cap before you seat it.<br /><br />That should give you the ability to keep the fire in, and water out; plus the right ign. timeing curve, and the longevity gained by corrosion resistance.

 

[seahorse5]

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

FEDERAL LAW:<br />183.410 Ignition Protection.<br />(a) Each electrical component must not ignite a propane gas and air mixture<br />that is 4.25 to 5.25 percent propane gas by volume surrounding the<br />electrical component when it is operated at each of its manufacturer<br />rated voltages and current loadings, unless it is isolated from gasoline<br />fuel sources, such as engines, and valves, connections, or other fittings in<br />vent lines, fill lines, distribution lines or on fuel tanks, in accordance with<br />paragraph (b) of this section.<br />An electrical component that is “ignition protected” is capable of operating in an explosive<br />environment without igniting that environment. “Ignition protection” of electrical devices is<br />accomplished by the use of seals, flame arrestors and potting (sealing), or a combination of such<br />means.<br /><br />An “ignition protected” component:<br />• will not ignite a flammable hydrocarbon mixture surrounding the device when an ignition<br />source causes an internal explosion, or;<br />• is incapable of releasing sufficient electrical or thermal energy to ignite a hydrocarbon<br />mixture; or<br />• has the source of ignition hermetically sealed.<br />A flammable hydrocarbon mixture is a mixture of gasoline and air, or propane and air, between the<br />lower explosive limit (LEL) and the upper explosive limit (UEL).<br />In general, the tests are conducted in an explosion chamber containing an explosive atmosphere,<br />defined by this regulation as a 4.25 (LEL) to 5.25 (UEL) percent mixture by volume of propane gas<br />and air. The mixture is introduced into the component where internal sparking occurs, or is induced,<br />so that an explosion is evident within the component. An internal explosion must not ignite the<br />explosive atmosphere surrounding the device in order for the component to pass the test. To assure<br />compliance of a component, this sequence is repeated 50 times. Propane, not gasoline, is used for<br />ignition protection tests because it is much easier to get repeatable results using this mixture rather<br />than gasoline vapor

 

[Don S]

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

Was thinking about the engine cutting out when the trim is operated problem, was wondering where the main power lead for the trim pump is hooked up.<br />Is should run from the main starter cable to a 50A fuse, from there to the down solenoid. If someone along the way hooked it in the wrong place, it could cause low voltage in the ignition system.

 

[Stan's Customs]

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

Thanks for the info Seahorse.<br /><br />Speaking of propane..it's used as a refrigerant commonly in Australia. Works good I've tried it.<br /><br />Anyway, doesn't that break down to waterproofing (sealing with a gasket, o-ring etc) and insulating the connections (heat shrink, silicone etc)..<br /><br />That's what I thought,at least, Winger Ed, but I thought I'd hit the forum with it. This is an OLD boat...I've got lotsa OLD parts, being in the restoration business. I'd like to use some of them so I'm not upside down in this OLD boat before I get it hittin' on 8 cylinders reliably.....That doesn't mean we arn't super particular, we are. <br /><br />Below my business name on my business cards, in parentheses and smaller print reads.....("formerly Alices REstaurant ") Those that know what that means are gettin' old or dead. Back when I started using it ..there was a well known song by Arlo Guthrie Guthrie called Alice's Restaurant...the chorus was "you can get anything you want, at Alice's Restaurant"<br /><br />That is our motto here...if you can think it up we can build it.<br /><br />I guess it is inherited, to me nohing it hard to do, if it is, develop a better way. That's because my Father would punish me for using the word can't. He would say "Son , there aint no such thing as can't" or "can't never did nothin".<br /><br />It was Ok to say I didn't know how to do this or that ...but not to say "I can't do this or that".<br /><br />He was born in 1899 an was a garage owner thru the depression into the early sixties...killed himself working (stroke) when I was 14. I believe he knew that I was going to "have " to do things very soon that I didn't think I could do.<br /><br />Thankfully ...it was the best legacy any man could leave his son...it has served me well....in all walks of life, especially in business. Everything is simple once you master it.....anything can be improved.,...which generally means "simplified".<br /><br />Sorry to ramble on..its a drizzly cold Sunday morning and the coffee's sure good..<br /><br />Beat Regards to all... hope your business is good this holiday season<br /><br />It so often is a hard time of the year for mechanics and vocational men everywhere.<br /><br />Stan

 

[rodbolt]

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

hello<br /> your ignition problem stems from a momentary voltage loss usually due to poor connections, splices and terminal ends. the sudden electrical load reduces the avalible current and voltage to operate the ignition system. the ign system electrons see the trim motor as a large short. they are lazy like me and would rather flow out the large"short" load than through the ignition system. <br /> fix your electrical system.<br />its kinda like a dragging starter on an automobile. if you turn on the headlights and hit the starter and the lights go out while the motor cranks you most likly have a poor cable or excessive current draw through the starter. tron,bass and me are all rather lazy .<br /> forget the HEI<br /> it does not work very well in a marine environment and was never made in a spark proof ignition protected form. there is no good way to seal it due to the coil/rotor button design.the USCG could care less about the system being water tight. its not a concern. they do however care about things blowing up. would not be so bad if it just removed fools from the gene pool. but sometimes bystanders and others get hurt as well.<br />occasionally explosive vapors will build up in the cap. the screens allow the vapors to dissipate and in the event of a small pop in the cap it will allow the expanding gasses to escape without blowing the cap off the distributor and allowing the flame to spread. the screen is a very carefully designed unit that will break up a flame and disburse it similar to the flame arrestor on the carb.<br /> I had a customer with an old bronco that would blow the cap off about every third time he tried to crank it. I told him for a year that the seals were worn. in a vehicle its not so big a problem, that capblowoff in a boat engine box could actually launch the box and start a boat fire.<br /> so when it comes to fuel and ignition parts take extra care. no splicing steel lines with tubing and hose clamps. no subsituting car stuff and off the shelf parts for marine stuff.

 

[Lou C]

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

I know many want to get rid of points and go with electronic, but these old OMCs are fussy with the ESA/electronic interaction unless the proper circuit to make it work is wired up. I am sticking with points since you just replace em once a season for the spring tune up, and I learned on cars with points so it is no big deal..<br />So maybe going back to the OE points type dist if you can find one may help....<br />Back to the problem, see if you can find the service bulletin, in the meantime, I would check every connection like Rodbolt says. If it was a salt water boat, you can see green corrosion wicking into batt cables, and you may also find a lot of corrosion on the starter solenoid + terminal (water drain for manifold just above it!) I put in a dual batt system last year, all new cables, cleaned all connections and grounds, and have had no problems with starting, or with the trim stumbling the motor for that matter. I also smeared OMC triple guard grease over all the connections that I re-did to keep the salt and moisture out. Now my cars have more corrosion on the batt terminals than the boat, which has none!!<br />BTW,I also got rid of the wingnuts on the batt and used nylock nuts to hold the cables on to regular auto style batt cable clamps, which also worked better than the wing nuts.

 

[Bondo]

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

Well Stan,<br />I admit I didn't follow your thread on the OMC Misses when trimming, Because it's OMC.......<br />But, After reading thru it, I think Don just Nailed the issue a couple posts above this 1.......<br />Where is the Power Tap for the Trim on your OMC ????<br />I think it's Not coming from the Battery, like a Merc., I think it's coming from the Ing. Circuit.. This will Overload the circuit, causing the stumble.... Feed it from the Battery......<br /><br />Now, back to the HEI,<br />(A little FYI, Sparks can Only Fly in a Straight Line)<br />Dist.s,+ Alt.s Must be Vented...... With all those Sparks flying around inside it, theres a build up of Ionized gases.. These Must be vented...<br />Venting is achieved by 1 of 3 methods.....<br />A) Screens.... Fine Screens are used in Dist.s,+ Alt.s... The screens will be in the Base of the Dist.,+ in All the vents on an Alt.... These screens are Grounded to the body of the unit....<br />When a spark tries to leave by way of a Screened Vent, it Can't pass through the Little Hole in the screen, because it Grounds out on the Screen, Inside the Dist., or Alt.....<br />B) Some Marine Dist.s use a little Brass Elbow in the Cap...... These work on the principle that Sparks Can't fly around Corners.........<br />C) Others use a little High-Hat vent... Same principle.... Sparks Can't turn 90*, much less 180*.........<br />BTW, Don't , I repeat, Don't Glue the Dist. Sealed Closed.........<br />The Build-up of the Ionized gases will cause All Sorts of Problems............... <br /><br />That covers the Dist.,+ Alt......<br />Starters are slightly different....<br />The older starters that we're all familiar with have an extra "Plate" inside.... This Plate mounts Between the Motor part,+ the Bendix drive part of the starter....... A very expensive plate, But it's the only difference........<br />If you up-grade to 1 of the New High-Torque Starters........ Automotive,+ Marine are Exactly the Same......... The Motor is Already Isolated, by the gear-reduction drive.........<br /><br />And, of course the Carb.........<br />Marine Carbs have the Float Bowl vented Into the bore of the Carb, rather than onto the manifold..... If it overflows, it'll dump Into the motor, Not Onto the motor...........<br /><br />The Merc. T-Bolt system is about the Best thing going.......<br />Relatively Simple.....<br />Dependable......<br />And, Good to about 6000RPMs........<br />

If the above is not an insurmountable issue..then what about the spark interruptor. ...How is it wired to the ignition

It's quite Simple............<br />When the Switch is activated, it Grounds Out the Ing..............<br />No Spark......

 

[Stan's Customs]

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

Thank you Don...<br /><br /> I will have to get more into it the next time I can get it home. I suspect you are right as Bondo also mentioned...the boat is down by the lake (90 miles) right now. <br /><br />Improper wiring "or" poor set up is definitely the cause. I don't believe the trim has a problem, it works perfect.<br />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. <br /><br /><br />Hello and thanks Rodbolt...<br /><br />The trim only affects the engine when bumped...when it continuously engaged it does not miss.(We talked about a voltage spike..this is more like a short) Unlike a dragging starter. It's something else..I think, as per above.<br /><br />I don't really want to use HEI unless I have to start buying marine distributors...the idea was to isolate the distributor by using a self contained simple unit that is in expensive and easy to isolate from the rest of the system(thereby eliminatimg the miss). Isolating the trim motor does the same thing (like Don S and Bondo have pointed out)...if that is the complete and only problem. Either way the ignition must be isolated and unaffected by outside accessories. Only problem is that my thoughts on isolating the distributor will not fix the problem, as I have discovered from these post...the whole ignition circuit is what has to be isolated ...<br /><br />I don't mean mean that you are not exactly right about the ignition seeing the trim draw as a large short. In fact that's the systems whole problem, I want the engine to continue to run sweetly up until the time the trim motor armature welds itself to the field coils and then it can die, miss or whatever. That evidently doesn't happen unless everything is just so so on these..I need a more bullet proof set up than that....so it can over come a "little" corosion etc., after all it's a boat it's gona get wet.<br /><br /><br />Hey Lou...<br /><br />Points worked good for years, just a little more maintenance. I think the problem on this rig would affect points too.. It's a brief ignition glich..short, over load ?<br /><br /><br />Well... what can I say Bondo...<br /><br />Thank you, seems hardly adequate for the time you spent explaining how these individual components function ...especially the distributor. I know marine carburetors, had some knowledge of marine alternators and starters, but knew very little about marine distrbutors. What an "excellent post"...I really appreciate the effort expended to clarify these points. It is extremely helpful.<br /><br />Thanks also for your concurring opinion with Don regarding the power source for the trim. I was trying to isolate the distributor from the system......if the trim is the total trouble source, isolating the trim will be much easier.<br /><br />When you say the shift interrupter grounds out the ignition. I am assuming that it is a simple grounded switch that goes directly to the coil whether I use the OMC or Mercruiser Shift interrupter? Correct-oo moon-doo ??<br /><br /><br />What a team...thank you all gentlemen, Most appreciated...<br /><br />Stan

 

[Stan's Customs]

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

One other thing ..<br /><br />The OMC Cobra 5.7 has a 1.41 overall gear ratio..<br /><br />Can anyone tell me what a 1979 260 Mercruiser gear ratio is...??<br /><br />I curious if I will have to reprop..when I change drives..<br /><br />Stan

 

[Don S]

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

You may have to change props, the prop sizes and pitches are determined by more than just the gear ratio. Has to do with hull design, weight, length, engine size, AND gear ratio. You still have to get the proper WOT rpm for the engine, and that is done through prop size and pitch.