Marston OA gearbox

[jerseydave69]

I'm currently working on/restoring my OA !
I'm struggling with taking apart the gearing from the gear case. I have the lower unit removed , and while turning the drive shaft ,the prop shaft wants to pull forward and come away from the pinion gear! It seems to me that there should be a thrust washer or something similar in there to keep it in place. With the rotor cover removed , if I push on the rotor back into to gear case ,it keeps the prop shaft engaged ,but then comes adrift again when I let go.
Also how does the rotor come away from the prop shaft ? It looks threaded onto the shaft ! Is it a left or right handed thread ? How do you grip the rotor to remove it ?
Thanks in advance

Dave

[Nudge]

You got a pic so we can see what the problem is?

[Oyster 49]

Post some pics, it's easier to understand what you are asking. We all like pictures

[Horsley-Anarak]

P.M. Charles L and he will run you through it.

He has had more of these in bits than most people and has seen lots.



H-A

[jerseydave69]

I will post a photo , but it won't really show you much ,because I can't see how the thing comes apart
Is the rotor a left or right handed thread ? I see you have yours removed ,so now I have an inking as to what is behind the rotor !
What tool did you use to remove it ?

Dave

[jerseydave69]

A photo, but doesn't show much !

[Oyster 49]

First question, is why are you taking it apart? There is an inherent risk when working on old motors like this, so only strip if you really need to!

[Adrian Dale]

A few photos of a strip down> This box has been fully stripped and rebushed. Photos show thread orientation and tools used. To remove the pinion you will need lots of heat. the puller is attached to the shaft (note the shaft is case hardened and to hold the set screw you will need to make a small divot in the shaft to locate the set screw) with a set screw in place, place blocks under the puller screws to avoid damage to casing. this is a very tricky box to strip and the risk of damage due to years of corrosion is high. But nice completed there is great satisfaction.

If you want more info PM but you have an expert right there in Jersey!!

Have fun but take care. Ill be stripping mine back down again later this month to prepare it for the Canal trip in the UK in June. Main reason is to check the rings and ensure reliability for the run

AJ

[Adrian Dale]

Rebuilt and ready for test.

AJ

[Oyster 49]

Hit it in one there. Do not attempt unless a. You need to, and b. Right tools available!

[JERSEYMAN]

Check your email Dave

[Charles uk]

Dave why have you taken your box apart?
20% of boxes taken apart, won't go back together, due to damaged threads by corrosion & cross threading.

From the little I can see your threads look ok.

There is a possibility that the front prop shaft bronze carrier is not fully screwed home, how much movement is there in the prop shaft? (in out)

[jerseydave69]

Thanks Rene , AJ and Charles for your advice and help, It's really appreciated .
The issue I have is that the prop shaft has forward and backwards lateral movement! Not a lot at all ,but enough for the gears to just catch each other. If I push on the face of the rotor while turning the drive shaft with my other hand , the gears ride perfectly. But if I don't hold the rotor face inwards ,it doesn't quite catch and seems to be coming out of gear... if that makes sense ! Oyster, This is the answer to your question as to why I wanted to strip it down, as explained in my initial post. That's the only reason I want to strip the box. But with the photo's from A J and Rene , I can almost "certainly" diagnose the problem! I think your on the money there Charles, as I'm pretty sure the brass carrier isn't screwed all the way down...allowing the prop shaft to move back and forth. This motor has been stripped down in the past. The piston was fitted upside down I noticed too !
Once I sort the issue , I will let you know
Thanks again

Dave

[JERSEYMAN]

So Dave.........you've come out of the Marston closet then!!

On a serious note only do the minimum you need to do to get it right, the alloy threads are soft and very fine and probably corroded, the impeller has to come off (RH thread) and you'll see where your at, I think Charles has got it though and if that's it you are laughing as long as the end cap goes back on, very easy to cross thread and ruin. I've done four and two are perfect and the other two, the end caps just spin which is strange as they were ok before and tight but once off became loose....that's a 50% failure rate before some serious machining.

The trickiest thing on these motors are the cylinders being in good condition, the pinion being a git to get out and those damn gearbox end caps, the rest is fun, rewarding and pure vanilla.

[Oyster 49]

Perhaps we should have a section on the forum to share information on these engines?