repairnh the Allison Gearbox

[Jasper]

Repairng the Allison Gearbox

After my last deep sea fishing trip, I lost thrust to the port side fwd engine. Reverse was still good.
After checking various causes, including re-building the Hydreco oil pressure pump, my mechanic said it was most likely the seals in the gearbox and the flywheel assembly.
So, yesterday we started the work in getting the gearbox off the motor and getting access to the flywheel at the rear of the motor. Lucky we have good access thanks to a well re-designed engine room. Thanks Merritts!

Unfortunately, it has turned into a lot more work than expected (doesn’t it ALWAYS!)

When we pulled the flywheel off, the clutch plate was almost worn back to bare metal and clutch material was all over the area. No wonder I found so little clutch material in the screen/filter in the early diagnosis time, there was not much left!
Also, the worn clutch plate meant metal to metal wear onto the piston, which is so badly gouged that we will have to get a replacement. Hopefully I can find one locally.
Looking for a cause we think we found it. The seals have a metal backing (brass?), and parts of this was all over the area. No wonder there was no oil pressure.
What amazes and even angers me, is that the previous owner had both engines replaced with fully overhauled 12V71n’s.
BUT left the original gearboxes. The starboard seems good. The oil stays fresh, while the port went black almost immediately.
Lesson learnt for next time: check that the gearbox was rebuilt when the engine was.
I will post more as we progress.

 

[Jasper]

Re: Repairng the Allison Gearbox

Next stage, getting the exhaust off.

 

[Jasper]

Re: Repairng the Allison Gearbox

Lifting the gearbox.

 

[Jasper]

Re: Repairng the Allison Gearbox

Flywheel removal and clutch!

 

[geofish]

At least you have a nice clean space to work in!

Try to locate the bearings locally and you should save a good chunk of cash rather than buying complete bearing kits.

US Bearings and Drives ( www.bearings.com ), Applied Industrial Technologies ( www.Applied.com ) are both good sources.

I fear I may have to do the same job soon... Every once in a while when I run WOT just before entering the harbor, it seems like I get an increase of rpms and a decrease of speed... It has happened 3 times to me and my hands were always on the throttles so I slowed immediately. then back up to 1900 with no problems...I don't do it anymore! did you experience anything similar prior to the complete failure?

BTW Nice pics

Good Luck and thanks for any comments

Geo

 

[Jasper]

At least you have a nice clean space to work in!

Try to locate the bearings locally and you should save a good chunk of cash rather than buying complete bearing kits.

US Bearings and Drives ( www.bearings.com ), Applied Industrial Technologies ( www.Applied.com ) are both good sources.

I fear I may have to do the same job soon... Every once in a while when I run WOT just before entering the harbor, it seems like I get an increase of rpms and a decrease of speed... It has happened 3 times to me and my hands were always on the throttles so I slowed immediately. then back up to 1900 with no problems...I don't do it anymore! did you experience anything similar prior to the complete failure?

BTW Nice pics

Good Luck and thanks for any comments

Geo

Thanks for the web sites, will keep them in mind.
As for the symptons you have, no, can't say I found the same. Started with delay in engaging of the the forward gear, then lack of some thrust, plus bad loss of oil pressure to the gearbox as soon as forward is engaged.. keep an eye on the oil pressure when the forward is engaged, then work through the different causes.
Good luck!

 

[MikeP]

Nice post -

One of my M20s has considerable delay - I'm guessing around 3-4 seconds - into forward for the first forward gear engagement when the boat hasn't been run for extended periods . Once that first shift has been made, there is no delay at all even if it doesn't run for a week or two. Operating pressure was slightly low and I could not adjust it up to spec so I did the HYD pump rebuild. Pressures were then normal but it had no effect on the shifting after extended non-running.

I suspect something similar to what you experienced is developing though in a subsequent call the folks at Arcadia said, "Don't worry about it, it's fairly common." Their view was that some trannies exhibit that behavior and some don't. I don't disagree that that may be the case - some trannies may have an inherent delay for the first shift after extended non-use but since the engagement delay after extended non-running is longer than it was a few years ago, obviously something is changing...

 

[Jasper]

Nice post -

One of my M20s has considerable delay - I'm guessing around 3-4 seconds - into forward for the first forward gear engagement when the boat hasn't been run for extended periods . Once that first shift has been made, there is no delay at all even if it doesn't run for a week or two. Operating pressure was slightly low and I could not adjust it up to spec so I did the HYD pump rebuild. Pressures were then normal but it had no effect on the shifting after extended non-running.

I suspect something similar to what you experienced is developing though in a subsequent call the folks at Arcadia said, "Don't worry about it, it's fairly common." Their view was that some trannies exhibit that behavior and some don't. I don't disagree that that may be the case - some trannies may have an inherent delay for the first shift after extended non-use but since the engagement delay after extended non-running is longer than it was a few years ago, obviously something is changing...

Hi Mike,
I have also been told that a delay of up to 4 or 5 seconds is "normal".
I guess when you consider how long this transmission has been running (could be 10 or 15 years), then you probably have nothing to worry about. Everyone tells me these are tough gearboxes.

 

[davidwigler]

Could your idle speed be slightly lower on the side with the delay? Try running the idle up by 50 rpm and see if it makes a difference.

 

[MikeP]

David - that's an excellent point that i hadn't thought about...

Yes, the idle on that engine IS lower by 50 RPM! It's the slave engine with the glendinning synchronizer. So per glen dinning specs, it's idle is set lower than the master engine (and it's governed top rpm is set higher).

When I get to the boat in a couple of weeks that will be one of the first things I check! I'll temporarily bump up the idle speed and see what happens.

Thanks!!

 

[Jasper]

Re: repairng the Allison Gearbox

Update:
I cannot get a piston over here, hard to believe considering how many Allison and Detroits are running “Downunder".
The piston is so badly gouged there is no chance of reconditioning it. So we have ordered a new one from www.dieselpro.com.
Cost is approx. $2,700 including shipping.
So the boat won’t be ready for the Easter holiday. Hope it is ready the week after!

 

[mike]

Try these guys, they will have them in stock, purchased 1 fwd piston from them a few years ago for well under $1000.00

Acadian Marine
21 Burgess Dr.
Broussard, LA 70518
337-837-3636
Brian Lemmon

 

[Jasper]

David - that's an excellent point that i hadn't thought about...

Yes, the idle on that engine IS lower by 50 RPM! It's the slave engine with the glendinning synchronizer. So per glen dinning specs, it's idle is set lower than the master engine (and it's governed top rpm is set higher).

When I get to the boat in a couple of weeks that will be one of the first things I check! I'll temporarily bump up the idle speed and see what happens.

Thanks!!

My Port engine is also the slave engine with the Glendinning synchro connected to where the rev counter would normally go. The synchroniser has never worked properly and would often not allow the engine to run normally once the synchro was disengaged. It will be interesting to see how it operates once everything is repaired.

 

[bobk]

My Port engine is also the slave engine with the Glendinning synchro connected to where the rev counter would normally go. The synchroniser has never worked properly and would often not allow the engine to run normally once the synchro was disengaged. It will be interesting to see how it operates once everything is repaired.

The folks at Glendinning are both knowledgeable and helpful. Email or call and you can get any help you need.

Bob

 

[rsmith]

Just FYI if your ever stuck somewhere with this problem. I had a friend that had the same problem with his 53 and got stuck in the Bahamas. No fwd only reverse. He and his family flew home and asked my son and I to bring the boat home for him. Not feeling like running for hours fighting one engine, we took the dive gear , prop puller and put the opposite spare wheel on that side. Ran home with that engine in reverse.

 

[Jasper]

Re: repairnG the Allison Gearbox

Thanks to all of you for the advice.
rsmith: your experience is good advice.
However, there is another way: while doing this job, the mechanic showed me how to "lock" the gear in forward if the same problem happened again and I needed to get home using the same engine.
There are 3 "plugs" (not sure what else to call these) at the front of the flywheel. If you screw these out, you will find 3 bolts. You need to turn the engine so that these 3 bolts show through the 3 openings. Then you remove these 3 bolts, remove the "spacer" nut from the bolts and then replace the nuts. These 3 nuts force/engage the gear into permanent forward to get you home, no clutch needed. Just make sure you start the engine at LOW revs.
Was a great thing to learn for the future.

 

[SKYCHENEY]

Re: repairnG the Allison Gearbox

Thanks to all of you for the advice.
rsmith: your experience is good advice.
However, there is another way: while doing this job, the mechanic showed me how to "lock" the gear in forward if the same problem happened again and I needed to get home using the same engine.
There are 3 "plugs" (not sure what else to call these) at the front of the flywheel. If you screw these out, you will find 3 bolts. You need to turn the engine so that these 3 bolts show through the 3 openings. Then you remove these 3 bolts, remove the "spacer" nut from the bolts and then replace the nuts. These 3 nuts force/engage the gear into permanent forward to get you home, no clutch needed. Just make sure you start the engine at LOW revs.
Was a great thing to learn for the future.

I know someone who did just that. Unfortunately, he forgot how to shut it down and ran under a bridge that was closing and ripped off his bimini top and antennas. It's really a great dock story after a few beers.

 

[Jasper]

Re: repairng the Allison Gearbox

Next stage of repairing the port gearbox, an Allison, finally is complete.

With the help of a very knowledgeable Detroit mechanic, I have learnt a lot about my engines and the gearbox.
We needed a new piston as the old one was so badly scoured due to the failed clutch.
I could not get one in Australia and ordered one from Dieselpro.com in the U.S. Within 6 days it arrived in Brisbane, Australia. Great service.

Next we removed the old rear main engine seal, then re assembled the flywheel, piston etc. and replaced the gearbox.

I had the sea trial yesterday and all seems good. Although the first 5 minutes were heart stopping when I found there was little thrust from the engine and the revs were going way past the normal W.O.T.
After going back to idle speed for a few minutes, then going to full throttle again and the prop now had “bite” and was running normal.
I think it was due to the Hydreco pump needing to prime itself.
Image 1:Flywheel
images 2 & 3 : New Piston

 

[Jasper]

Re: repairng the Allison Gearbox

Attached Images:
New Clutch.
Rear Main Engine Seal.
Removing the old engine seal.

Removing the rear main engine seal was a bit of work. First we tried with a screwdriver, but finally had to drill the outer metal part of the seal to break it and then pull it out.

 

[Jasper]

Re: repairng the Allison Gearbox

Finally re-installing the gearbox