Gray 6-71

[Jerzyguy39]

I have a 28 ft silverton with 318 chrysler engines with V drive trannies and iam not happy with them ....
Top speed is only about 20 and just dosent seem to be a good fit they just seem to be struggling ...
I came across two GRAY MARINE 6-71 DETROIT DIESEL never installed ..
My question . is would it be feiseble for me to stip those gas engines out and replace them with the two grays ..
First will they buckle up to the V drives second what kind of speed would i get .. ive asked a few local friends they arent really specialist .. but one saids he thought the ratio was to low that they werent built for speed and that to gain on speed would nt happen
and iam also hearing that with a boat my size 28 ft and a motor of this tork that 1 engine would be sufficient that a second 6-71 would be a waste ..
IS there any motor heads that can eloborate on this .. Thank Ken

[Guest62110524]

your 6/71s are too heavy even if they ar highly rated
the diesels for thisare the 4 cyl yanmars, or the 4 cyl volvos
but they are expensive new
I dont know you cockpit layout , but the 6cyl of both make would be good as a single installation or best of all a 6bt 5.9 Cummins if you have the heaight in c pit
you may troll the second hand engine websites

[pogie joe]

Hi Ken, GM 6-71 with HV 70 injectors is only about 165 HP on a good day. You also need to check on rotation, some rotations can be changed in some reverse gears and some can't, if you need to change rotation of engine the labor in some cases would exceed the value of the engine Most of those engines came from the factory with SAE #1 housing's that were matched with Twin-Disc manual gears. I don't think your problems is going to be your V drives.The weight on these engines bobtail, as i recall is about 1800 lbs w/o gear and about 2200 lbs w/gear. Then the other issue is clearance and so on not to mention poor fuel economy. If you decide to buy these engines make sure you invest in some good hearing protection. My advice would stay away from the 6-71's you maybe better off with a pair of cheap 3208 cats with a 72 series Borg-Warner gear.

[Guest62110524]

Originally Posted by pogie joe

Hi Ken, GM 6-71 with HV 70 injectors is only about 165 HP on a good day. You also need to check on rotation, some rotations can be changed in some reverse gears and some can't, if you need to change rotation of engine the labor in some cases would exceed the value of the engine Most of those engines came from the factory with SAE #1 housing's that were matched with Twin-Disc manual gears. I don't think your problems is going to be your V drives.The weight on these engines bobtail, as i recall is about 1800 lbs w/o gear and about 2200 lbs w/gear. Then the other issue is clearance and so on not to mention poor fuel economy. If you decide to buy these engines make sure you invest in some good hearing protection. My advice would stay away from the 6-71's you maybe better off with a pair of cheap 3208 cats with a 72 series Borg-Warner gear.

3208? at 600kg apiece and would he have big enough fuel tanks, the engs I mentioned would use fraction of the fuel ,
i am sorry that is not good advice, although you do know your engines

[rasorinc]

Don't use the 6-71s way to heavy Why not rebuild the 318s. ther are dozens of marine shops that do this and can add 60-100 hp for you, here is an article on gas vs diesel. by Pascoe who has written many many books on boats.. those are good reliable engines so rebuild or exchange and get more hp. the engines are just tired.http://www.yachtsurvey.com/GasDiesel.htm
there is a part 2 to this article

l here is a link to rebuilt 318s http://www.autoelf.com/shop/motor/ch...op_318mlb.html
SAVE $$$ if that is important. Hope all this info helps you.

[pogie joe]

Woosh, when i said 3208's w/a 72s B-W Gear i was thinking in terms of money only, if Ken was looking @ 60 year old engines I'm sure he is not going to put long money in a short money boat as you suggested.

[pogie joe]

Woosh, i reread your post and you did say look at used engines, you are correct, please accept my apology.

[Guest62110524]

I thought I did suggest 2nd hand?
3208,s would nearly sink his boat , anyways Peace!
IMO, a single cummins 5.9 second hand is a good option

[Jerzyguy39]

Thanks guys for all the responces after reading all the responces i think the best way to go .. is with Rasorinc idea . Actually i looked into rebuilding both engines ... and it was 1200 each... which i thought wasent to bad
Theses are the orignally engines to a 1974 boat .. so hes right their most likely tired ... i would love to have twin diesels but the cost iam sure would be to great for a pleasure/ bay fishing boat ... besides theses 6-71'S .. or to heavy for my silverton ....if anyone is interested those motors are listed at this time on ebay .. i expect they will sell fairly cheap ..
i'll link it here below thanks again......Ken

http://cgi.ebay.com/ebaymotors/Parts...1%7C240%3A1318

[Guest62110524]

http://boatdiesel.com/Forums/ForumIn...C=1280:1024:32
just troll here,
I think yes the rebuild is good idea, watch the heat excahngers tho(if you have em) they are v expensive

[rasorinc]

Whoosh, Check out these prices on marine manifolds. Stan
http://www.marineparts.com/BarrManifolds/Barr9.aspx
and these. http://www.ebasicpower.com/
more...http://www.marineparts.com/partspage.../crusader1.htm

[eponodyne]

318s and 360s have the same block, and I know for a stone fact you can massage a 360 to over 400 HP with no worries at all.

You might be overpropped or the boat might just be too damn heavy. I'd guess it's weight.

[Jerzyguy39]

To be honest eponodyne its probaly a combination of several issues .. to heavy (10,000) pounds dry weight / motors are tired ../ and it has a fly bridge with a custom built hard top that iam sure isnt to areo dinamic .. but im thinking mostly engines .. iam going to have them rebuilt and bored 30.over. and see how that works out ..
Thanks again everyone for all the input .. Ken

[Gilbert]

I think you are on the right track with the idea to overhaul the engines. I didn't see anything about props and such here. ONE 318 should get you 20 mph or better on this boat if the reduction and prop are right for the weight and etc.

[eponodyne]

What can you do to take some weight out of the boat? Do you really need everything you're carrying around? Could you sit on thinner pads and sleep on an air mattress? Like that.