Jump to content

BMC 2.52 rear crankshaft oil seal


boatman.robin

Featured Posts

Hi everyone,

 

I am in the process of changing the rear crankshaft oil seal on my engine. Gaining access to the seal is a mission so I want to make sure I do it well, and to be honest I have already messed up a brand new seal that got stuck on a slight angle despite all my most gentle efforts.
I have seen that some models have a bolted flange that you can just put the seal into with a bit of RTV and that flange will guide the seal nicely around the crankshaft. My engine does not have that.

Some engines have a wear sleeve around the crankshaft. Not mine as far as I can tell.

 

1. Is there a trick to getting the seal on uniformly without a special tool?

 

2. Is my engine missing any parts from previous dodgy repairs? It seems the seal is not quite touching the visible part of the shaft that has the bolts holes on when in place.

 

3. Below the shaft there are 2 bolts. I have noticed that the washers on those bolts are free to spin but the bolts seem tight so maybe they are too long. I fear that oil is coming through those as well. Can I change them or do they hold something inside that will fall if I take them out? Can I seal them with RTV?

 

Attached are a few pictures,

 

Thank you for your time!

7607318C-5B36-4834-BC6C-B5963519179B.jpeg

BD437012-969B-45FF-9F82-BCB6D1E75DFF.jpeg

Link to comment
Share on other sites

I assume we are looking at the engine back plate. I think (don't hold me to it) that those small bolts go into the rear main. To be honest from your photo it looks like engine out, invert and sump off to to see what is going on. Do you know your hot tick over oil pressure?

 

If the 2.5 is anything like the 2.2 there are seals either side of the rear man and I think a cork strip in a  recess in the main bearing cap between the cap and back plate.

Link to comment
Share on other sites

Hey Tony, cheers for the response.

 

I don’t have the option to take the engine out in the near future, but I could try and crawl underneath and get the sump off.


When you say rear main, is that main bearing? Hot engine pressure is 50/60psi.

 

I can’t see anything in the manual about any other seals in the manual. Attached is the diagrams and the crankshaft removal / refitting procedure. The only seal they mention is the one I’m trying to change.

D4C390CF-D00A-4069-8602-B1FCF38C7EDC.jpeg

8C865D00-0876-4ED0-A9F5-FCF6C7E591CB.jpeg

819227D5-C7E6-408E-8C16-FE765D412FDC.jpeg

Edited by boatman.robin
Adding info
Link to comment
Share on other sites

If that oil pressure is hot at idle then taking the amount of out of alignment that photo shows between seal and crankshaft The I do not believe it. if it is a true oil pressure than the rear main bearing is probably OK. I think the 2.2 (can't say for the 2.5) had dowels to accurately locate the back plate onto the block. If those have been left out there would be nothing ensuring the back plate is concentric with the crankshaft. there is always a little play between bolts and their holes. I think some of the bolts may have been dowel bolts that have an oversized shank to do the same job, if so changing them for ordinary bolts or possibly putting them in the wrong hole would have a similar effect.

 

The bearings that support the crankshaft in the block come in two halves. One half fits up into an "arch" in the block casting while the other half fits into other castings that bolt up against the block. These bearings are known as main bearings (as opposed to big end bearings) and the casting the bottom half fits into is the main bearing cap.

 

For the crankshaft to be as far out of alignment as it appears to be the possibilities are:

 

The back plate s not accurately located on the block.

The main bearings are very badly worn.

For some reason the main bearing cap is loose.

 

You could try taking the back plate off to see if the crankshaft is concentric with the main bearing but you will need a new gasket and if one is fitted that cork strip.

Link to comment
Share on other sites

The old seal doesn’t seem evenly worn so it is very possible that something is misaligned indeed. God this might be turning into a far mor extensive repair than I previously thought…

 

I have been using a really big ratchet strap to support the engine on the floor beams when taking out the bell housing as two of the engine mounts are on the bell housing. That back plate ensures that the strap doesn’t slip so if I was to remove it I would have to completely take the engine out I guess…

 

Thanks again Tony, I remember reading your website in the past. Kudos for sharing useful info for newbies like me!

Link to comment
Share on other sites

Good advice.

 

I should’ve mentioned it earlier but there was rattling in the bell housing when the engine ran and I did find a broken spring in the bell housing wish a imagine comes from the starter (which surprisingly works fine).

I guess it’s possible that the bits of spring got in the way of the flywheel spinning and knocked it out of axis.

Link to comment
Share on other sites

The spring might have come from the drive plate.

 

I really can't see a spring knocking the crankshaft out of axis or even bending it That is what you are suggesting. Have you ever seen  the crankshaft and how it is fixed into the engine? I think either the engine would stop or something else would break, possibly the bell housing.

 

I note some details are not shown on the exploded view you posted, there are no back plate/bell housing bolts for a start

Link to comment
Share on other sites

20 minutes ago, Tony Brooks said:

The spring might have come from the drive plate.

This makes so much sense!

 

I have not seen the crankshaft yet. I imagine you suggest that it is really strongly bolted.

 

I just talked to another mechanic who says you’ve given me good advice and I should investigate what you suggest.

 

I will do that and post my findings here so it can help someone else in the future.

Link to comment
Share on other sites

The back plate is falling off the engine block. You will have to take it off and find out why, the seal will not work like that. There are dowels to locate it, the bolts do not locate it correctly. If the dowels are gone you need to find some. You can use rollers from an old bearing if they are the correct size. They have to be hardened steel or they will shear in use. Plain ends off twist drills will do if you can cut them with a grinder without overheating and softening them.

All the bolts/machine screws will most likely be damaged and need replacing. They are unified threads, UNC into the block and main bearing caps.

Edited by Tracy D'arth
Link to comment
Share on other sites

37 minutes ago, boatman.robin said:

Thank you Tracy.

 

That’s now 3 people concurring on the issue. It’s good to know what I’m chasing!

 

It sounds as if this may be a far easier fix than initially thought although the back plate/flywheel housing (whichever it is) will have to come off.  If it is a marine flywheel housing I just hope it has been drilled for the dowels. I would suggest that you do a temporary fix with the old seal in place so you can judge if the seal and crankshaft are then concentric and if they are take it off and fit the new seal before refitting it.

 

If there are any dowels in place you may have to gently tap and/or lever the back plate off the block.

57 minutes ago, Tracy D'arth said:

There are dowels to locate it

Thanks for confirming the 2.5 uses dowels and that my memory is not quiet shot,

Link to comment
Share on other sites

Ok my engine is only 2 cylinder but I lifted it off its mounts at the rear with a Spanish windlass made from 12mm rope and a length of stout wood. You could use your webbing the windlass can give you a lot of force to lift. I hung the rope off a strong piece of timber accross the floor and then when it was supported wiggled and packed some timber underneath the engine clear of the bell housing, seal etc. I then released the Spanish windlass and cleared it all out of the way and access to the bearing was simple. Didn’t need a jack and getting the wood packing in was possible easier than using a jack. Hope this may help

Link to comment
Share on other sites

  • 2 weeks later...

Hey everyone,

 

So i finished that repair last week. The back plate was actually where it needed to be. That gap between the seal and the crankshaft was just an optical illusion due to the fact that the seal is tapered inside.

To insert the seal I used a hole saw that happened to be the right diameter and protected the new seal from the teeth with the old seal. Gently tapping all around with a hammer and the seal went in all right.

Thank you all for your input, I learnt a lot!

  • Greenie 1
Link to comment
Share on other sites

35 minutes ago, boatman.robin said:

Hey everyone,

 

So i finished that repair last week. The back plate was actually where it needed to be. That gap between the seal and the crankshaft was just an optical illusion due to the fact that the seal is tapered inside.

To insert the seal I used a hole saw that happened to be the right diameter and protected the new seal from the teeth with the old seal. Gently tapping all around with a hammer and the seal went in all right.

Thank you all for your input, I learnt a lot!

Glad it worked out, you had us worried with that photo, we thought the backplate was falling off!

 

Thanks for the update, not enough folk give us the outcome.

Link to comment
Share on other sites

9 minutes ago, Tracy D'arth said:

Glad it worked out, you had us worried with that photo, we thought the backplate was falling off!

😊 hahaha sorry! I also cut back the two bolts on which the washers were lose. They were definitely too long. My engine has a lot of randomly replaced bolts on it…

 

10 minutes ago, Tracy D'arth said:

Thanks for the update, not enough folk give us the outcome.

My pleasure, respect has to be paid when people give you their time to help :)

Link to comment
Share on other sites

Thank you for thanking me!

By the way, as I think it could be useful info for someone with oil leaks as well, it seems my breather is clogged. I am going to take care of it in the afternoon. Not asking for help, just thought I’d mention it for noobs like me as it can be a source of failing seals.

best wishes to you all and thanks again for your advice!

Link to comment
Share on other sites

I can't remember if the breather is the same as the smaller engines but if it is the side breather on the tappet chest cover often has a mesh inside, better to remove the cover so that you can soak the mesh in solvent or petrol to clean it. The cover has a thick cork gasket which usually can be reused.

Edited by Tracy D'arth
Link to comment
Share on other sites

I think it is mounted on the full length side cover and on the 2.2s was just an open pipe hanging down. I suspect on the 2.5 it has a vertical section of large bore "pipe" with wire mesh in it. They do block and if it is like this I would cut the end off the large section, pull all the mesh out and replace with a stainless steel pan scourer. Then weld or solder the top back on.  BMC had a habit if using ordinary steel mesh and by now it could be a rusty mess.

Link to comment
Share on other sites

Finally pulled that oil separator / breather out today. It was a bit blocked but not too terrible. I plunged it in a bucket of soapy hot water and quickly pushed a finger in and out of the engine side hole (I tried really hard to formulate this in a way that doesn’t sound sexual). It worked really well as I could see a jet of water coming out the exit pipe.

@Tony Brooks I could feel the mesh and it seemed in good condition so I will avoid popping the can open for now, but thank you for the recommendation!

I also cleaned my air filter holder which was very oily and the flexible hose.

The whole shabang is now drying. Fingers crossed it does the trick!

Edited by boatman.robin
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.