BUKH gearbox removal in situ -HELP!

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VicMallows

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I am having great difficulty removing the gearbox from my BUKH20 with the engine in situ in the boat (Sadler 29). The top 3 nuts (13mm) released easily; but the 2 nuts underneath are proving impossible to release, almost certainly due to the restricted access and the fact that only an open-ended spanner will fit. (they have been soaked in penetrating oil for a week). Rear of engine is jacked up as far as possible to improve access.

Any clever suggestions ...... seems ridiculous to lift the engine out just to undo two bolts! Is there a clever spanner I do not know about?

Many Thanks. Vic
 
The old saying of "it's always the last that won't undo" seems to be applying here.

I would suggest replacing the nuts already removed and do them up tight. Then have another go at undoing the bottom two nuts. It may be the weight of the geabox hanging on them that is jamming the two bottom nuts.

The best practice when undoing (or tightening) a number of nuts or bolts in a circle is to undo opposites but only half a turn until you know all are moving. This prevents any distortion causing them to jam.

Also tightening them before trying to undo them sometimes helps.
 
A beam across the hatchway, a 4 part pulley off that and a plank underneath will get it into the cabin. takes about an hour.

Then you can see what you're doing.


Done so with a DV10 several times, it helps to remove the flywheel first.
 
chewi said:
A beam across the hatchway, a 4 part pulley off that and a plank underneath will get it into the cabin. takes about an hour.

Then you can see what you're doing.


Done so with a DV10 several times, it helps to remove the flywheel first.
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I did much the same. The two lower bolts on my Bukh 20 were corroded and proved very difficult even with the engine and box in the saloon. I lifted the engine using a turfer, not ideal but I was abroad at the time. I lowered it onto a skateboard on a plank and rolled it down into the saloon.
 
Many thanks for all the helpful suggestions.

Today I ground down a ring spanner to about 3mm which enabled it to fit and freed one of the 2 troublesome nuts. Hopefully I can achieve the same on the other (port side) nut .... in theory should be easier as the force will be downwards. (in some cases the studs are turning rather than the nuts, but that is of no consequence).

A custom-made crows-foot would be ideal, but it would need a much longer offset than any standard one. A half-moon could indeed help, but would again need grinding down in thickness, or converting to open-end.

I agree I could fairly easily move the engine into the cabin, but I'm not sure access would be any better in the Sadler29 cabin.

Thanks again, and will report when all is well. Vic.
 
vyv_cox said:
I did much the same. The two lower bolts on my Bukh 20 were corroded and proved very difficult even with the engine and box in the saloon. I lifted the engine using a turfer, not ideal but I was abroad at the time. I lowered it onto a skateboard on a plank and rolled it down into the saloon.
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I also just did the same on my Sadler 34. What job are you going to do when you have the gearbox off? Crankshaft seal? Much easier to do with engine out!
 
SimonJ said:
What job are you going to do when you have the gearbox off? Crankshaft seal?
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Simon, Essential job is the gearbox input shaft seal (did the output one 2 years ago, but oil is now draining out of the input end in under an hour when running).

My intention is to replace the rear crankshaft seal at the same time (though no engine oil leakage at present). It seems from the diagrams that it should be simple once the gearbox is off, even with engine in place? .... Am I missing something??

Vic 'SUNDASH' 29
 
I finally managed to remove the gearbox by hoisting the rear of the engine up as far as possible with a rope around the block just forward of the gearbox and a 16-1 purchase to the boom end. Front mounting bolts were slackened, but probably still put an excessive strain on the mounts; however I am renewing them anyway.

The oil leak was in fact from a crack in the front gearbox casting around the STB engine bracket mounting holes, not from the input shaft seal.

For info, the input shaft seal CANNOT be replaced from outside, even though the manual seems to imply this. It is necessary to split the gearbox casing (which is easy enough) to replace the seal from the inside. (The output shaft seal is replaced from the outside and is easily done with the gearbox in situ).

Vic
 
VicMallows said:
I finally managed to remove the gearbox by hoisting the rear of the engine up as far as possible with a rope around the block just forward of the gearbox and a 16-1 purchase to the boom end. Front mounting bolts were slackened, but probably still put an excessive strain on the mounts; however I am renewing them anyway.

The oil leak was in fact from a crack in the front gearbox casting around the STB engine bracket mounting holes, not from the input shaft seal.

For info, the input shaft seal CANNOT be replaced from outside, even though the manual seems to imply this. It is necessary to split the gearbox casing (which is easy enough) to replace the seal from the inside. (The output shaft seal is replaced from the outside and is easily done with the gearbox in situ).

Vic
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hello Vic
Have a similar job coming up over the winter - input shaft seal on my BW6 gearbox (at least I hope its the seal). From your description it sounds like you have the BW7? Would be interested to know how you got on with the cracked casing.

I'm also planing to change the engines rear crankshaft seal (bukh 20) while I'm at it. Any tips on this appreciated.
 
cimo said:
I'm also planing to change the engines rear crankshaft seal (bukh 20) while I'm at it. Any tips on this appreciated.
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You have the manual? You can download it at http://motoren.ath.cx/menus/bukh.php
Note that on page G3, dismounting of rear end cover, the manual omits removal of the drive flange and nut! Otherwise the job is pretty straightforward. On page G11, dismounting of manual governor, the drawing is confusing. The long leg of the spring faces down, not up as apparently shown.
 
cimo said:
Would be interested to know how you got on with the cracked casing.

I'm also planing to change the engines rear crankshaft seal (bukh 20) while I'm at it. Any tips on this appreciated.
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I had the casting welded (by C&B Marine, Chichester Marina). As well as the crack, they built up substantially on the inside to add physical strength. (Cost was around £50 inc VAT). I'm fairly sure the failure was caused by collapse of one or more of the engine mounts. I have since done about 20hrs motoring and so far all is well! I have pics of the crack before repair, but unfortunately in my keenness to get the job finished forgot to get 'after' pics of the weld before closing up the gearbox. (Will post on this thread when I get around to it).

Still puzzles me why the rear of the engine is supported on the light alloy gearbox casting, rather than directly on the engine block, but looking at all the engines at the Boat Show this appears universal.

-------------

Rear Crankshaft Seal:

I was surprised to come across the coupling/shock-absorber between gearbox and engine! .... as Vyv says it is not shown/mentioned anywhere in the manual under either the engine or the BW-7. (I now see it IS shown in the BW-6 section which I had not previously looked at).

I used a 3-leg puller to remove the engine-side coupling, but it didn't come off easily. After soaking in penetrating oil I did the puller up as tight as possible and left it for a day. A sharp tap on the puller then freed it. (I have read advice elsewhere not to do the coupling up too tight if you ever want to remove it again!). After getting it off I did notice that their are 2 M6 tapped holes ...... I am guessing that these are so you can PUSH the coupling off against the block by doing up a couple of bolts without needing a puller .... could be wrong though.
(EDIT: If the coupling is tight that would put a horrible strain on the crankshaft bearings so I AM WRONG)

Once the coupling is off, the seal can be easily removed by drilling a couple of small holes in the face and screwing in self-tappers to pull it out. When replacing, note that the seal simply sits in the plain bore (there is no ridge for it to bottom against. It's important therefore to make sure it sits square and is not pushed in too far. 2-3mm seems right. Seal needs a suitable adhesive sealant. (My first attempt went wrong and had to destroy seal and start again). Parts Manual gives the seal as 35-50-7 but the original factory seal was 35-50-8 and I found this size easier to position.

Hope this is of use, Vic
 
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VicMallows said:
......

After getting it off I did notice that their are 2 M6 tapped holes ...... I am guessing that these are so you can PUSH the coupling off against the block by doing up a couple of bolts without needing a puller .... could be wrong though.
(EDIT: If the coupling is tight that would put a horrible strain on the crankshaft bearings so I AM WRONG)

......
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There is a picture of he Bukh puller at the front of the workshop manual. The puller has 2 screws which fix into the 2 M6 tapped holes.

J
 
RestlessL said:
There is a picture of he Bukh puller at the front of the workshop manual. The puller has 2 screws which fix into the 2 M6 tapped holes.

J
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Yes. Good example of RTFM :) .... though not sure I would have recognised the description "puller for flexible coupling" , given that the manual does not indicate the presence of said coupling. Suitable tool could easily be made from any piece of steel bar.
Anyway, it was good to put my 'universal puller' to use for about the third time in it's 40 year life :D
 
vyv_cox said:
dismounting of manual governor, the drawing is confusing. The long leg of the spring faces down, not up as apparently shown.
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VicMallows said:
Seal needs a suitable adhesive sealant................ Parts Manual gives the seal as 35-50-7 but the original factory seal was 35-50-8 and I found this size easier to position.
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much thanks folks

I found the workshop manual somewhat lacking when it comes to the rear engine crankshaft seal. It's not entirely clear if rear cover removal is necessary or not. Taking the engine out soon - next week or two all going to plan - so expect more questions from me!

Any recommendations regards the modern day equivalent for "seal adhesive sealant"?

rgds
c
 
tube.JPG

this leak eluded me for over a year.
when stationary, the oil level would hold. When under power, this hole in the dipstick tube (much bigger now) would empty the gearbox within 6 hours. As it turns out, both shaft seals are perfect.
 
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