Lets talk engine dilemas

[bigfella68]

I am building a traditional ski / runabout which is just short of 16 feet, its a Build A Boat Silver Spray, as I am not much into ripping around the place anymore rather then go for a V8 I have opted to use a Ford 6 cylinder 250cu engine, the engine I am using is the alloy head version to save some wieght and I am using the earlier XD Falcon manifold and Strommy as I dont need the unreliability of the Webber on the water, the most this boat will ever do is pull my wife on the skis or the kiddys in the ski bicky, this is where some knowledge is needed, the drive! I was thinking two things either just straight shaft running of the harmonic balancer or a dog clutch, let me use the word budget build here first so a dog clutch is out of my reach so I making my own, heres where the advice is needed, has anyone ever attempted to make there own drive? I am thinking of using a small transfer case froma Suzuki Sierra as its tiny and light, it gives me a nuetral feature which I need and a forward gear which is good, at least I can nuetralise the thing going backwards isnt necessary the old oar will sort any moving away from the bank duties.
I am choosing to use the stock exhaust manifold I figure I can wrap it inlarge amounts of heatproof header tape and I can also line the engine box with some heat proof gear as well, the drive thing is what is vexing me the most at the moment, I dont think anyone uses driect drives anymore?
I have other issues like wether to use an oil cooler as in the remote type or modify the sump with copper pipes to cool the oil using fresh water, happy to chat with anyone who has been there and done it but welcome all input.

[PAR]

I've made several automotive to marine conversions including using automotive manual transmissions and clutches to provide reverse and neutral. First let me say it can be done and has been done, but there are several bases you need to cover first.

First off, you can't use a dry exhaust in an enclosed engine space. Regardless of the amount of "header wrapping" you apply to the manifold, the heat build up will quickly melt down every wire, rubber and plastic piece (like electrical connectors) in the engine box. Trust me on this, I've tried it, have seen others that have tried it and you just can't provide enough volume of air passing through the closed compartment, to keep the heat below 300 degrees (F), below 250 is preferred.. Vapor lock will be the least of your worries.

Second, it's extremely important you use marine starters, alternators and carburetors. The reason is they will not cause an explosion, like an automotive unit will. Marine carburetors have O rings on throttle and choke butterfly shafts, to prevent vapors from escaping and collecting at the bottom of the engine compartment. They also have several other marine only features to prevent vapor lose. Starters and alternators have spark arresting shielding to keep them from touch off the vapors that may have collected.

Next is cooling, you can use a closed water system, but it's got the same air flow problem. You just can't suck enough air through the radiator and blow it out of an engine compartment fast enough to keep the ideal engine temperature, within a closed engine box. On an engine like that, you'll need in the neighborhood of a full sq. meter of inlet and likely twice that much of an outlet to vent the now heated air. Those are two really big holes in an engine box, which doesn't do much for noise, not to mention standing anywhere near it.

Cooling can be done a number of different ways. The common ways are closed loop heat exchanger or raw water straight through a wet exhaust. The heat exchanger still uses a wet exhaust, but isolates the engine cooling in a closed loop (anti freeze and all), removing the bulk of the compartment heat with the wet exhaust and separate raw water pump. You can have a closed loop engine system and use a "keel cooler", but this is basically the same thing as an engine mounted exchanger, just the heat exchanger is externally mounted. The pure raw water system literally pumps raw lake water through the engine and manifolds, then back over the side. This type of system needs only one water pump, but if running in salt water, you'll eat up the cooling jackets on an automotive engine surprisingly fast.

The only successful "air cooled" arrangements I've seen are completely exposed engines (usually with a pretty chrome blower mounted on top) or ones where the engine bay was isolated and open to permit cooling. Work boats have used this type of system, dry stacks and all, but they're noisy and hot to be near.

The drive can be any manual transmission that can bolt or adapt to the Ford 6. We used to use 3 speed truck manuals out of GM pickups. Typically high gear was the only gear we used, with many removing first and second to shave a few pounds off the spinning assembly. A heavy duty clutch is necessary as you'll wear it out fairly quickly. This is because you can't just ease it out and have the engine not stall. You have to "dump" it, which eats up clutch plates pretty rapidly. Most of us used a simple clutch peddle and clutch fork arrangement stolen directly from a donor car. Some invested in a hydraulic system, which is also a simple thing.

I know some guys that have used automatics, but they had as many difficulties as we did. In most cases the valve body pressure had to be dramatically increased with shim stock, just to get it to shift and playing with different size torque converters, etc. to launch the boats with the violence necessary to keep the prop spinning as it tries to shove a stationary boat forward.

These were all straight shaft setups and we raced them as kids, before we had families to feed, to eat up all our excess money.

The first thing you should do is figure out what the max RPM your engine will spin at under 100% load. Next the prop that can spin at that RPM and drive the weight of your boat. If the two can't be found, then you need a gear reduction to bring them closer in line with each other.

Considering the complexity and fabricating necessary to make these home made systems work reliably, you should strongly consider finding a used Velvet or Paragon drive. These two boat transmissions can mate to just about anything or can be adapted to anything. They shift reliably, are easy to repair and parts are plentiful.

[bigfella68]

Some valuable information there specially regarding the manifold heat, the other option I have here is an old set of header pipes I have I can simply fit a pipe case around it to run the water through for cooling I was going to plumb the water through the exhaust in any case, I didnt think it would generate a great deal of heat as plenty of boats run the factory manifolds would guess she wouldnt run much hotter then 70 to 80 degrees cel, I plan to run the air cleaner on top of the engine box and will be very mindfull of leaks I dont here of too many ski boats going up in smoke but it does happen, vigilance on behalf of the owner and an extensive maintenance program will help, the carby modification can be done here thats nothing new, I am aware of petrol and how dangerous it can be in a confined space, I heard that one cup of evaporated petrol in a confined space is equal to 3 sticks of gelignite, makes you think twice!!! it will only see fresh water use so corroding the block out doesnt scare me too much in any case I will flush it through with fresh water after each run,
The gearbox idea is interesting, a truck type box would be way too heavy even when stripped of the rubbish, you dont think the transfer case idea has merit, even at minimum revs you dont think it would engage from nuetral?, in my youth my brother and I had a small Sprint Car, it ran a Nissan A series engine, the dog clutch in that was home made using an extension housing of a Rolls Royce Gearbox, quiet simply you bolted a gear onto the crank and slipped on the unit, we used to push start the thing to get it going but on occasions whilst under way you could nuetral the thing and even re engage it though the gear life was reduced, I would have thought that in a boat with no resistance the unit could be engaged and disengaged without problem but I could be wrong I quiet often am!, I estimate the maximum RPMs were talking here would be 4- 4500, beyond that the bottom end strength worries me having owned many Ford 6s over the years, nice and torquey motor and very reliable but there not bombproof, you can get 140HP out of one with out doing too much to the thing ,though should get a skier up and out of the hole ok, would probably estimate top speed somewhere between 35 - 45 MPH, as I said I am doing this one on the cheap so If I can make do with something I will use it, I just want to get out on the water drag the kiddies about in the ski bicky and do it for the least amount possible.

[Stringy]

last year I rebuilt an old ski boat and investigated many these areas.

Firstly I looked at replacing the original engine with a V6 commodore engine but marinising it started to get out of hand $ wise. Ended up rebuilding the original engine.

My boat is direct drive from the crank snout not flywheel end, having never owned or driven anything bigger than our canoe I was concerned so spoke to several old blokes who owned this type of boat including 1 mechanic who had a couple of timber direct drives. The consensus was that there was no problems with this type of drive and to leave good enough alone. Since then the boat has been out skiing regularly and the dog box owners seem to be using the box for warm up and that is it, rarely is there a good comment about them. Velvet drive owners with reverse seem to love these boxes - I understand they are Borg Warner forklift gearboxes, if this helps. These engines sit high and I don't know how this affects the boat and prop shaft angle.

What are you using to handle the prop thrust? Your crank shaft will not survive without some sort of thrust bearing, I would imagine the velvet drives are probably modified or must have an external thrust bearing, same as automotive gearboxes have no provision to handle thrust!

[PAR]

Velvet drives do accomidate thrust and can handle a lot of power, certianly more then that six will offer. I have one that is eating 300 HP.

Headers work, but only if the box has no top. Generaly they are mounted upside down so the pipes swing up and out of the box. The thin wall tubing that headers are made from will not tolerate water being splashed on them very long before they brun through.

Home made manifolds can be made, but it's some pretty fancy fabrication and welding work.

You'll need a marine cam for the automotive motor to work well. Marine engines have basically two speeds, idle and WOT. They aren't intended to be as "flexible" as land based variants, because they don't have gears to accommodate different loads. Marine engines run at 90% to 100% power output, 90% of the time. While automotive engines run at 30% to 40% output 80% of the time. You can see why you'll need a different grind on the cam.


A marine carb costs just about the same as a new automotive unit. You'll not save much by attempting to machine O ring grooves in shaftways or bowl vent loops into the venturi.

Install a spark arrestor air cleaner, even if you do exstend the air intake out of the box. I don't know how bad your harbor patrols are down there, but ours will have a fit if they see a conventional air cleaner on an enclosed engine. I know the likelyhood of a spark reaching down to the compartment in an external mount, is remote, but they're cops, not engineers, so if it doesn't conform to what they're use to, they don't try to think about it, they just write a summons.

In such a small boat, why not an outboard? Steering control and responce are far better, the units are generaly much lighter then straight shaft setups and you'll gain a huge amount of room in the cockpit.

[bigfella68]

Nah raspberries to the out board idea, the plans are for inboard and I want an inboard after having outboards, the direct drive is sounding better, after all one can warm it up on the trailer prior to plonking it in the drink so that way you merely point in the direction you want to go and turn the key, I understand about the camshaft biz I did allow for a new cam in my thinking, this thrust biz has me a bit phazed, having seen many inboard ski boats whilst I was contemplating my own machine I did see a couple of old Ramsays with direct drives on old Y Block Fords and they just had the original flywheel and the adaptor for the crank and that was that, some time ago whilst out hunting I came across the remains of an old timber ski boat in a paddock under a tree, it had been running a Sidewacker V8 it used a belt drive with a pulley on the shaft and a belt of the front of the motor, I will look into the marine carby biz but again I havent seen one a Ski boat locally yet, mostly Holleys. I have owned dozens of old Fords and I am yet to have a fuel leak but not saying it doesnt happen, accident do happen. Back to thrust , I need to get an angle on this thrust biz, bueaty of forums is you can hash out all these ideas before running off half cocked and making a major blunder. Speak to my all knowledgable uncle and see what he says, Thanks Gents
With the Camshafts, American engines generally run alot of pollution control gear and have smog cams which hinder performance, over here our old motors are smog free, the engine I am using is a 1974 Ford 250cu it has no smog cam, it also runs a single barrel Stromberg Carby which are as a rule reliable , It wasnt really until 1976 did we see some pollution gear even then it was only a simple charcoal cannister and a carb bowl vent hose and a purge hose to the aircleaner, when the XFlow Ford 6 came into being did we start seeing EGR valves and thermostatic controlled things most of which was useless as we didnt enforce the maintenance on early smog engines and to a degree we still dont, enough about Ford history, I will take all replys on board and do whats best.

[bigfella68]

I had a conversation with my uncle who is a retired engineer / toolmaker, he reckons the thrust issue with the Ford is a no worrys thing as the Ford 6 has an internal thrust bearing on the crank and doubts it will give trouble, we talked about modifying a Transfer case to use as a gearbox, he thinks it will shift ok with low RPM idle, I think I will go with the straight shaft drive, who needs reverse.

[Kev da Fridgee]

The comments Paul has made regarding manifolds and carby's is good advice, we had an 18 foot hartley, 380 HP (dyno HP) Windsor and a three stage hamilton Jet as our familly runabout for 14 years and never had a problem with over heating, there are several manufacturers around for Exh manifolds, we had "Rolco" Ally standard type configuration and yep you can get em for the six as thats what was in the jet boat when we bought it, actullay it was an older cast iron head but they are available so hunt one down. I made the heat exchangers out of two lenghts of 1 and 5/8 copper about 1.5 meters with 11 1/4 copper tubes inside and that engine ran at 85 deg C all day all night at any rev range no matter what and sommetimes we loaded that boat with enough gear to drop it about 8 inches below the water line. As far as carby's go we "marinised" the holley without much drama, O rings, teflon seals and gaskets etc AND a quality spark/flame arrestor there not expensive and I have personally seen the job they do, same goes for the Starter and Alternator, all this is pretty easy to do if you seek out the info and is the cheapest way of making sure there is no BOOM when you turn the key, along with maybe a bilge exhaust fan.

Bottom line is get the right accessories and you will never have a drama

[bigfella68]

I had alook at Rolco tonite I printed of the 250 Ford items and they list a manifold which I think I will go with, there are some other bits I can use too, are engines rigid mounted as in no rubbers?, I have seen marine starters and alts about the starter for the Ford 6 would easy enough to get I guess, the alt would be no dramas its a common Bosch unit and besides anything can be made to fit its just brackets, they didnt list a water pump block off plate but I can make one easy enough, I like the heat exchanger idea well worth doing, I dont like the old pipes in the sump they crack and fill your motor with water real fast, a small remote oil cooler would be wise too, the blower fan is on my list every inboard should have a blower fan, I will pay alot attention to the fuel and electrics and make sure its as safe as humanly possible. K&N turn out some nice marine arrestors for the carby, I will fit a fuel shut off tap and a deadmans switch, I am gathering much information from all this, I appreciate it.

[Kev da Fridgee]

We made brackets to suit the standard engine mounts, the bell housing on both the 250 and the 302 were rolco and we used mounts from Blackwoods or Repco from memory. Just take in some info like expected weight on the mount, whether or not minimal deflection is needed or not, intended use etc etc. Not sure if the shaft drive you will use can handle soft mounts, on the jet installation it uses a double uni so a little movement is ok and sure beats the hell out of vibrating the crap out of a lightly built hull.

we also used the standard water pump as with the heat exchangers you still need it, interestingly we didn't use any oil cooler but had good ventillation through the bilge and out through a transom vent and never had any oil degradation, we did use an oil suitable for extreme use though as at the time i was also into drag racing so had used a few different oils in cars etc

[bigfella68]

The use of boat will be mainly just cruising and towing ski tubes, its no race boat and doesnt need to go like a stung cat, I am too old for thrill seeking these days.

[Stringy]

"Marine engines have basically two speeds, idle and WOT". I am having trouble accepting this, this is how it works with my old boat; Towing tubes 1800 to 2200rpm, kneeboards 1800 to 2000rpm, skiers 2600 to 3000rpm (about 26 to 30mph), flat bickie with 4 people 4200rpm (about 48mph). Pulling a skier up requires good torque from idle and smooth carburation. My engine is good for 4500rpm but I think the prop is a bit over pitched, it's an Austral 12 13 but has been pitched up at some stage.

"after all one can warm it up on the trailer prior to plonking it in the drink so that way you merely point in the direction you want to go and turn the key". I have a lopey cam, idle screwed down as low as possible and no chokes and am yet to have a problem warming it up in the water, don't know if it would be good for your skeg bush to run it dry! I slip my prop shaft out of the drive when running on a hose.

"he reckons the thrust issue with the Ford is a no worrys thing as the Ford 6 has an internal thrust bearing on the crank and doubts it will give trouble". I would be very interested to find out more regarding this!

All automotive engines have thrust bearings to handle crank end play/float but none are designed to actually handle external thrust. I have been searching and found little information because no one runs direct drives now! With the "V" drive, dogbox or velvet drive handling the thrust. I have even had a look for engine mount/girdle/thrust plate housings with no sucess.

Just spoke to an old bloke who was into racing these things and am about to go and see him now.

[bigfella68]

Think I have a handle on this heat exchanger biz, what your saying is to run a fresh system but replacing the radiator with a heat exchanger and using outside water to cool it, the cooling water would still need to sourced via a pick up and run through the exchanger and then out the exhaust, do you need to run a header tank with this or some sort of expansion chamber? this is why you say I can retain the original water pump and thermostat set up? am I on the right track here

[Kev da Fridgee]

Hi big fella, your on the right track, we made our own header tank for the fresh water side, and a fllow restrictor on the raw water as with the jet the flow was to great and created a few problems, there are quite a few different brands around and you shouldn't have too many problems finding one. I got your PM and as soon as I get to the shed to dig through some of the old info I will send some to you.

[bigfella68]

I will get my uncle to make the header tank and heat exchanger hes done heapsof that stuff, easy for him.,
I remember years ago I looked at an old carvel chugger at Lemon Tree Passage she had been used around the Oyster plots, about 25 feet with a Perkins Dieso they had a FWC system on that which consisted of a big beer keg, she sucked it out the bottom and poured it back in the top, whole thing was bodgey including the boat, nothing scares me more then an old timber boat specially one with bitumised hull timber below the floor, couldnt get of it fast enough. I keep thinking if you hit something hard enough the bow would spring open and then your noah food. Only ever been on one boat that sunk and that was as a child in Port Augusta in SA my dad had an old open putt putt, very popular in those days with the fisherman, had an old prefect motor in it, dad replaced the inlet hose but rather then cut it too length he ust coiled it under the floor boards, we get up into the Red Banks and something lets go and the old thing sank real quick luckily we were close to the bank and were able to get out real quick, I have alot of respect for sharks and do my utmost to stay out of there back yard, so its fresh water lakes for me.