Help and advise wanted on foam engine bearers

[PerformanceDodge]

Hi, I am converting a 225 Honda Cougar from out board to inboard engine. The stringers and bearers are foam cored. I do not really want to take them out and replace them with wood, I would like to stick to the originals, it would save a lot of work and they are quite well built.

My idea is to drill 2 horizontal holes 300mm apart through each bearer with a 50mm hole cutter.

Then insert a 2 x 50mm diameter aluminium insert in each bearer that finish flush with the outer vertical external faces of the engine bearers.

Then glass over sides and top of the bearer with a thickness of around 5mm.

Then make a U channel in 3mm stainless to cap over the top and down the sides of the engine bearers.

Then bolt horizontally through the whole lot at the centres of the inserts with 10 mm bolts.

The engine mounts would the bolt to the top of the U channel that now caps the top of the bearers.

The weight of the engine is around 210Kg.

Does any one think will work OK or is there a traditional way to do it.

Has anyone got any photo's of how there's is done or better idears.

Any advise would be much appreciated.

[Jon Fuller]

I think that principle will work ok. Though personally I would make (fabricate) your channel, with much thicker section for the top cap (3mm is probably fine for the verticals) and also make it such that the cap sits very close to the top of the longit (thats now been strengthened with extra glass) so that you can bed that U channel down on some Crestomer or similar, that way you're not relying on the horizontal fixings being in 'shear', as all the (very high) G loads will be taken through directly into the top of the longit. If the cap thickness were enough (say 10, or 12mm) you could drill & tap directly into it. Probably easier, cheaper etc to make that capping assy in steel, and powder coat it, rather than SS. SS is a pain in the arse. (IMHO)

[Jono]

Originally Posted by Jon Fuller

. SS is a pain in the arse. (IMHO)

Big girl's blouse......

[Jon Fuller]

I'll take the choice of 'No response' to your somewhat pointed comment!

The reason for my choice of silence.....please refer to your signature.

[biffer]

seem's like a lot of work, you could do them as pic in foam or wood, layed inside the matt is a 12mmx100mmx300mm steel plate, we drill and tap engine mounts straight into it

[PerformanceDodge]

Many thanks for all your replies, and photo's all the advise is much appreciated. Also thank you to Hydrostream for the PM.

I have also designed fabricated my own engine mounts using polyurethane bushes. All though I have never seen this method used on boats it was used in Ford escort rally cars many years ago and seemed to stand up to a lot of punishment.

I have tested them for deflection with a vertical load on a press and they deflect about 8mm with a 1 ton vertical loading. This equates to a 200kg engine at about 5 G's of force.

Does any one know if this mounting method has been tried successfully in boats before.

Regards David

[Jon Fuller]

What diameter is that vertical stud?

[PerformanceDodge]

Originally Posted by Jon Fuller

What diameter is that vertical stud?

Hi Jon and thanks for your replies

The vertical stud is 16mm, the horizontal bolt is 16mm shoulder bolt. The O/D of the polyurethane bush load bearing surface is 60mm. There is also a 24mm bush/space trough the centre. The polyurethane bush is in 2 halves separated by a 4mm thick washer 60mm dia with a 44mm hole trough the centre. The idea is if the bush failed the engine can only move 10mm max side to side and up and down, hopefully enough to limp home. It is all made from 316 stainless bar the bolt which are 304 I believe.

I have left the base plate round at the moment so it can be trimmed to size at a later when I have decided exactly where the bolts are going.

Kind regards David

[Jon Fuller]

Your engine is lighter than what I'm used to, but the 16mm / 5/8" stud options from the mainstream mob (merc, R&D etc) aren't up to it. I've always used the 3/4" UNF option (19mm, but imp fine thread) As side landings, that sometimes can't be avoided, put that stud under enormous side load. I have bent countless 3/4"UNF ones when racing (and in my pleasure boat). I now set things up so there's no thread showing between the motor foot, and mount, using washers/spacers as shims to achieve the correct height, rather than a lower adjustable nut. This obviously increases the vertical member diameter to the size of the OD of the spacers/washers, making it very bend resistant. Bit more fiddly setting up engine alignment, but worth it (IMHO).

If your engine 'gets let loose' in the engine bay at speed, feck knows what damage will be done!

[PerformanceDodge]

Originally Posted by Jon Fuller

Your engine is lighter than what I'm used to, but the 16mm / 5/8" stud options from the mainstream mob (merc, R&D etc) aren't up to it. I've always used the 3/4" UNF option (19mm, but fine) As side landings, that sometimes can't be avoided, put that stud under enormous side load. I have bent countless 3/4"UNF ones when racing. I now set things up so there's no thread showing between the motor foot, and mount, using washers/spacers, rather than a lower nut. this obviously increases the vertical member diameter to the size of the OD of the spacers/washers, making it very bend resistant. Bit more fiddly setting up engine alignment, but worth it (IMHO).

If your engine 'gets let loose' in the engine bay at speed, feck knows what damage will be done!

I am actually amazed that you bent 3/4 bolts, that really takes some doing.

Hmmm, that a worrying though a loose engine. The studs were actually hex head bolts with the heads turned down but in hind sight it may be a better idea if I was to take them back off and weld the new bolts back to the mount. This would give me a shoulder so it could be packed with shims, spacers or washers instead of the bottom nut then it would be unlikely to bend the thread. Thats a good idea, thanks Jon.

I have noticed that some Mercruiser engines have an additional front engine mount, do you think I should have one and what is the purpose ??

Kind regards David

[Jon Fuller]

That bell housing looks like a nice piece of work! very posh.

Front mount? are you sure it was in addition to the regular port & std mounts? some small 4 cyl mercs only had the rear bell housing mounts, and a single front jobbie.

Great project, looking fwd to it's completion.

Is that block ali?

I'm gonna sound a real pessimist here, but I think I would consider a brace around/under the block tying the mounts together, like a horseshoe (we have this on the Swipes raceboat). I've heard that G meters on race boats have measured as high as 50g spikes, hence the large stock of bent mounts I/we used to have.

You definitely don't want a cracked or broken block. Ask any Yanmar owner / racer. TD and I ripped the side out of a 502 EFI Merc in a rough race once. we went to solid race mounts/plate after that, but that's not really an option on a diesel if you wanna keep your teeth.

[gazza]

Is that block ali?

There's a clue in the first post.

Would def go more heavy duty bolts 3/4 in high tensile.

[Jon Fuller]

Originally Posted by gazza

Is that block ali?

There's a clue in the first post.

Are you still here?

[gazza]

I know your Ginger but I do like you coz your so funny

[PerformanceDodge]

Originally Posted by Jon Fuller

That bell housing looks like a nice piece of work! very posh.

Front mount? are you sure it was in addition to the regular port & std mounts? some small 4 cyl mercs only had the rear bell housing mounts, and a single front jobbie.

Great project, looking fwd to it's completion.

Is that block ali?

I'm gonna sound a real pessimist here, but I think I would consider a brace around/under the block tying the mounts together, like a horseshoe (we have this on the Swipes raceboat). I've heard that G meters on race boats have measured as high as 50g spikes, hence the large stock of bent mounts I/we used to have.

You definitely don't want a cracked or broken block. Ask any Yanmar owner / racer. TD and I ripped the side out of a 502 EFI Merc in a rough race once. we went to solid race mounts/plate after that, but that's not really an option on a diesel if you wanna keep your teeth.

Hi Jon you are correct just looked at the photo's of the Mercruiser and it is a four cylinder and has no centre mounts.

The Mercedes engine is quite a piece of design work, it is an all aluminium engine with cast in cast iron liners, cross bolted crank and counter balance shaft in the centre of the V to stop vibration. It is built like a Swiss watch, the only gaskets are the head and exhaust gaskets everything else is 'O' ring or sealant.

A brace between the two engine mounts sounds a good idea especially with my foam cored bearers, if its not too cheeky just wonder if you have a photo of your brace just to give me a few ideas.

Was a bit stumped with the bell housing when it came to aligning the rear transom mounts until I realised the crank shaft has a 35mm recess in the end to accept a bearing for the manual clutch version, I then realised that the drive shaft support bearing in the outer transom plate is also coincidently 35mm ID. So I ordered a piece of Silver steal ground to exactly 35mm and this made the perfect alignment tool so I could weld the bush mounts to the bell housing accurately.

The drive plate I have used is from a Mercruiser 7.4MPI which I believe are rated at 310bhp, if I have problems there is a heavy duty version which has s/s splines. The outer diameter is turned down to about 10in dia and bolted to the fly wheel with 12 x 8mm bolts around the circumference. I am also using the 7.4MPI raw water pump mounted where the air con pump was.

[Jon Fuller]

The Drive plate on our Steyr's is a reduced diameter version, probably about the 10" you speak of. Might have fitted, or been close. still, you seem to have all that under control.
J

[NIC SURRY]

Originally Posted by Jon Fuller

That bell housing looks like a nice piece of work! very posh.

Front mount? are you sure it was in addition to the regular port & std mounts? some small 4 cyl mercs only had the rear bell housing mounts, and a single front jobbie.

Great project, looking fwd to it's completion.

Is that block ali?

I'm gonna sound a real pessimist here, but I think I would consider a brace around/under the block tying the mounts together, like a horseshoe (we have this on the Swipes raceboat). I've heard that G meters on race boats have measured as high as 50g spikes, hence the large stock of bent mounts I/we used to have.

You definitely don't want a cracked or broken block. Ask any Yanmar owner / racer. TD and I ripped the side out of a 502 EFI Merc in a rough race once. we went to solid race mounts/plate after that, but that's not really an option on a diesel if you wanna keep your teeth.

This project is very interesting,with regard to engine mountings and the probelems you have expereienced with the side mounting ripping out of the block,would the engine mounting set up as used by drag cars not be more suitable ie the flat plate bolted to the front of the block spanning the stringers as this could be used at the front and the back of the block,just a thought ?

[Jon Fuller]

Yeah, the solid race mounts I refered to earlier are similar to that, but with the NVH you get from a diesel, it would be unbearable to solid mount (hence the comment about losing ones teeth) Certainly for pleasure use anyway.
The first mounts I tried in 'Maelstrom' (single engine V8 diesel Extreme) were std Merc petrol V8 metalastic mounts, the vibration was extraordinary, so I had to do some research that finally let me to R&D Marine, who did suitable alternatives, ie, strong enough to take the riggors of sport boating whilst holding up a 1/2 ton diesel engine, but soft enough to get rid of the awfull vibration. (and I do mean awful)
I used the same R&D units in Leviathan.

[PerformanceDodge]

Originally Posted by Jon Fuller

The Drive plate on our Steyr's is a reduced diameter version, probably about the 10" you speak of. Might have fitted, or been close. still, you seem to have all that under control.
J

Wish I had known about the Steyr's reduced diameter plate, as it would have been better to use an of the shelf item that didn't need to be modified to fit. Is this a Steyr or Merc part ?

[Jon Fuller]

It looks like merc, the rubber doughnut etc is identical to merc, even painted blick. I assume they custom make em for Steyr, or whoever wants to use their drives.