Bottom End Blues!

Nasher · 08 August 2005, 12:13

Hello All

Well, the bargain buy Suzuki 200EFI I fitted to my Ocean 6.25 has now been thoroughly tested, and It appears to be all I hoped it would be. Its Quiet, appears to use less fuel, doesn’t mind running at low revs for a while, and goes like stink. I bottled out at 49 Knots it the slightly choppy Solent yesterday without even trying to trim the engine properly.
Cruising at 25 – 30 Knots the engine sounded very happy at under 4000RPM.
Thanks to Mark Halliday and family for letting me tag along on their day out.

But, it’s developed a nasty looking crack about 3 inches long in what I thought at first was the gearbox.
However, it’s only in the Exhaust chamber behind the prop, and the oil in the box has drained out as fresh as when I put it in a few weeks ago. I do need to sort it out though to stop it spreading and to restore full strength.

It looks like it’s been welded before, judging by the small blow holes around the crack, and the back of the weld can be seen in the chamber where it was inaccessible to clean up. Annoyingly when it was welded whoever did it didn’t strip out the retaining ring for the bearing ‘spider’ and its now welded to the casing.

I’m obviously going to look for a good condition bottom end to sort it out properly, but will get the Dremmel out tonight to clean out the crack ready for welding. I’ll have to go with the legacy I’ve been left and leave it assembled.

I understand there is a company in Southampton that repairs outboard casings, like welding on a new skeg, does anybody have their details?
They will have more experience of the alloy used, so I’d rather try them than my usual friendly welder in Portsmouth.

Also of course, does anybody know of a good condition bottom end for a 99 Suzuki DT200HP EFI hanging around anywhere? Rocking Horse poo springs to mind!

Nasher.

codprawn · 08 August 2005, 12:20

Before you try welding it have a look at a metal filled epoxy - they can be VERY effective - have a little bit more flexibility than a weld so don't crack so easily.

You MUST make sure that there is no oil or grease present - use a solvent to clean very carefully.

I have seen the stuff used on all sorts of gearbox casings and even cylinder heads to fill pitts caused by head skimming.

codprawn · 08 August 2005, 12:21

By the way what sort of fuel figures are you getting - I am soon to have a 225efi which everyone has told me will bleed me dry..........

Nasher · 08 August 2005, 12:42

Codprawn

Hi. Thanks for the epoxy tip, i'll give it a try. I'll wait to grind out the crack until I'm ready to use the epoxy, that way it will be clean.

Having used it only once, I can't say for sure about the fuel, its just that the gauge appeared to have moved less for a few hours use.

Remember I'm comparing it to an old Johnson 150VRO that I used to run around at full throttle ALL the time, where as the new engine is doing less than 4000RPM at a crusing speed of 25 - 30knots and about half throttle.

Nasher.

Nos4r2 · 08 August 2005, 13:11

Codprawn is right about the epoxy-I've even used JB weld to repair a cracked water jacket on a 4.5 litre leyland petrol engine and a year later it was still good.

If you do decide to get it welded then leave the company doing it to do all the weld prep-unless you know what you're doing with that specific alloy then they may have to redo it anyway-or at worst you may clean out too much without realising and cause a problem.(One of my many trades is a Brit Standard certified welder) Jap alloy is a bitch to weld as it's usually pretty poor quality and cracks easily while cooling after welding

A couple of things I will suggest is
1)drain the lower unit oil and leave the drain plug out-otherwise you run the risk of the heat blowing the seals out as the contents of the lower unit expand. In my experience with welding casings on Jap bike engine casings it needs to be left to cool fairly slowly or cracking at the weld site appears.
2)Take the prop off and clean any oily residue out of the exhaust chamber with gunk, clean that off and flush with copious amounts of spray brake cleaner or pure alcohol afterwards. Gunk leaves an oily residue but will get the majority of crap out to start with.

codprawn · 08 August 2005, 13:51

Quote:

Originally Posted by Nasher

Codprawn

Hi. Thanks for the epoxy tip, i'll give it a try. I'll wait to grind out the crack until I'm ready to use the epoxy, that way it will be clean.
.

Nasher.

Don't just grind it - use solvents as well - loads of it.

Talking of solvent hypervalue and other £ shops sell aerosols of brake cleaner for a quid or less - basically it is trichloroethelyne judging by the smell - great stuff and a lot cheaper than some of the other branded products.

Nasher · 08 August 2005, 16:05

Thanks guys, I’ll try using the epoxy first, and if it cracks again I’ll get it welded. I’ll have to grind out some of the crack to get any epoxy in to begin with as it’s only about 0.25mm at its widest. I’ll also drill a 1.5 or 2mm hole in the end of the crack to try and stop it propagating, then fill that with epoxy too.

I like to think I can wield a MIG pretty well, so I borrowed a TIG and tried welding a Jap bike engine case myself when I converted my old Z1 to hydraulic clutch (see www.simonnash.co.uk) I gave up and gave it to somebody who really knows what they are doing.

Can you recommend a brand of epoxy to use?

If anybody wants to poke, prod, or generally draw breath at it, I’ll drop it in the back of my car for the Solent meet tonight.

Nasher.

stan_deezy · 08 August 2005, 16:15

JB Weld is very good for this sort of job: available at B&Q or Halfords

Andy · 08 August 2005, 20:58

I would not trust this again until its welded.

This is not an uncommon problem and as it stands sounds like it will weld up. However if the crack travels you may loose part of the gearbox as it will litterally fall out, that case is holding the whole lot in. You can afford to loose bits into the sea, once they are gone they are lost. Also you will end up stranded. Just strip the gearbox out and have it welded. Don't let them grind the weld off the outside, just leave it, its stronger. Dont do it yourself the stuff is a bitch. You need a specialist.

This happened to one of my outboards, once done it totally fine.

codprawn · 08 August 2005, 21:26

You would be suprised how well epoxy can work in the right circumstances - I have used araldite 24hr with metal fillings in it - whatever metal for the job in hand - cast iron for cast iron etc etc. I have personally done a few engine blocks that have lasted years.

When welding aluminium TIG is the only way to go - ideally the part needs to be pre heated as well.

Seriously epoxy is well worth a try - JB weld is very good but almost any slow setting epoxy with metal filler will do - remember Aston Martins and the new Airbus are all glued together!!!!

codprawn · 08 August 2005, 21:30

Forgot - Lumiweld is also supposed top be pretty good but never used it myself.

http://www.frost.co.uk/item_Detail.asp?productID=8823

Frost are a great site - all sorts of great stuff for car buffs but much of it usefull for RIBS as well...........

Matt · 08 August 2005, 21:31

For a reasonably non structural component - agreed
For something with a large surface area of contact - agree

But, I think you completely underestimate the loads that are transmitted through the gearbox. That's 200HP! Plus all the shock loads it takes when romping along in the rough stuff.

Nasher · 08 August 2005, 23:35

Going to think about this one overnight.

Obviously if I had the choice I'd strip it out and get it welded, however as mentioned the previous repair I found has welded the bearing retaining ring into the casing, so it would have to be welded whilst still assembled, and run the risk of wrecking the bearings. Or a lot of metal would need removing to get the ring out.

I'll let you all know how I get on.

Nasher.

codprawn · 08 August 2005, 23:45

Quote:

Originally Posted by MadMat

For a reasonably non structural component - agreed
For something with a large surface area of contact - agree

But, I think you completely underestimate the loads that are transmitted through the gearbox. That's 200HP! Plus all the shock loads it takes when romping along in the rough stuff.

It all depends on where the crack is - without seeing a photo or diagram it is a bit hard to comment.

As to the loads transmitted through the gearbox i would have thought they actually go through the gears and shafts - obviously some boxes are more stressed than others - F1 cars for example use the gearbox as the mounting for the suspension!!!

Nos4r2 · 09 August 2005, 03:28

Quote:

Originally Posted by Andy

Don't let them grind the weld off the outside, just leave it, its stronger.

Wrong. If it's welded PROPERLY its stronger with the proud weld ground off and polished smooth. Any irregularities (such as a raised weld) have the potential to start a crack-this is why conrods on racing motors are polished. After welding cast aluminium (or any metal) the grain structure of the casting is affected and has the potential to start a crack forming due to the differing grain properties at the boundary of the weld material and the original material.

BTW-I should have read the original post properly-if the bearing retaining ring has been welded up by accident then it's going to be close enough to a stressed area that it WILL need welding-epoxy isn't going to be strong enough and the crack is likely to spread. Besides, if you grind it out to epoxy it then you'll make more work or possibly make it impossible to weld. IF the guy welding it misses one tiny particle of epoxy then it'll blow holes in the weld.

Andy · 09 August 2005, 09:15

Quote:

Originally Posted by Nos4r2

Wrong. If it's welded PROPERLY its stronger with the proud weld ground off and polished smooth.

Interesting ... the people that welded my box with the same defect, said in their experience the crack is better left without being ground down. From what I remember they suggested that the thinkness of the metal, brittleness of the metal, and the heat/vibration caused by the grinding process all where factors in them recommending I did not request it to be grinded. Hence I have my weld bead visible. Maybe they just could not be arsed and fobbed me off, I have no idea.

Its made no difference to the performance of the engine. It does not look bad its looks like a good job.

Matt · 09 August 2005, 09:37

Just take a step back and think about it again.

What holds all these very strong shafts, gears and bearings in place, exactly?

Quote:

Originally Posted by codprawn

As to the loads transmitted through the gearbox i would have thought they actually go through the gears and shafts

Matt · 09 August 2005, 09:41

Reaching the limit of my knowledge here, but I think it's to do firstly with the hardness/structure of the metal in and around the weld that's been affected by the heat, secondly by the stress riser in the shape of weld itself, and thirdly from stresses induced in the welding process itself. You often get a welded up component cracking again along the edge of the weld.

Quote:

Originally Posted by Andy

Interesting ... the people that welded my box with the same defect, said in their experience the crack is better left without being ground down. From what I remember they suggested that the thinkness of the metal, brittleness of the metal, and the heat/vibration caused by the grinding process all where factors in them recommending I did not request it to be grinded. Hence I have my weld bead visible. Maybe they just could not be arsed and fobbed me off, I have no idea.

Its made no difference to the performance of the engine. It does not look bad its looks like a good job.

Nasher · 09 August 2005, 09:59

I’ve had another good look at it this morning before I left for work and decided I’ll try to get it welded. Mainly because it’s not very thick, so even if I grind it out to 45 deg the Epoxy will not have a big area to bond to.

I agree by the way that removing the weld bead is the stronger way to go.
The joint between the old surface and the edge of the bead is a stress former. If left the bead, being thicker, is stiffer than the surrounding thinner metal concentrating any minute movements to the joint between the two. Over time the joint may fracture, particularly as the heat from the weld may have upset the metallurgy of the casting in the surrounding areas. Although this can be reduced by cooling slowly.

I’m not having much luck locating a used casting, so the old one is looking more and more precious.

Nasher.

codprawn · 09 August 2005, 12:10

Quote:

Originally Posted by MadMat

Just take a step back and think about it again.

What holds all these very strong shafts, gears and bearings in place, exactly?

Obviously the casing - as I said it all depends on the design. Remember - unless a bearing is siezed there shouldn't be much force on it unless it is a thrust bearing.