Half Moons & Oil Return Tube (Head to Block)

[Hamish Coutts]

I seem to remember Keith (Type 26 Owner & technical Guru) posting something on the deterioration of the black 'rubber' half moons he found when dismantling a twink head. They seem to have softened and expanded.

I recently stripped my cyl head for inspection and found exactly the same thing. The half moons were in a really poor state - all soft and horrible and it looked like they were becoming perished - the rubber was sticky. As far as I can find out from the previous owner, they were renewed when the engine was last rebuilt about 10,000 miles & 2 years ago. Yes, that's 10k - the engine is being stripped to investigate low compression pressure in no4 cyl and piston slap, bummer.
However, back to the subject, I find this worrying that the rubber can deteriorate over such a short time and get into such a state. Also the oil return tube was in the same condition as the hole through it had nearly closed up! It had also expanded and softened.
As far as I can make out, mineral oil has always been used.

I will be rebuilding the engine soon so will need new rubber parts. Question is, how long will they last? Will they need to be replaced in a couple of years? Or were the ones used the last time just crap - sorry, inferior quality?
Has anybody else had experience of this and if so, are there any fixes to this problem - is it the oil? Does this also happen with synthetic oil? Do oil additives (e.g. STP) have any effect?
I don't want to have the hassle of replacing these parts unnecessarily.

Has anybody got any ideas to improve the situation, or any alternatives?

Regards,

Hamish.

[carrierdave]

Hi Hamish,
About 6 months ago I stripped my engine. It had not been run or touched for 27 years and had only covered 58K miles before that. Looking at the engine I do not believe that it had ever been apart.

Both the half moons and the head return tube were in good order ? There was no stickiness to them at all; the rubber was as good as the day it had been installed so it can only be the quality of the material or something put into the engine at some point.

Were any sealants used on the half moons and tube? Sometimes you can have a reaction between the sealant and the rubber.

The other possibility is engine flush, did the previous owner use some sort of aggressive engine flush to clean the engine through ? this maybe aggressive to the rubber.

Apart from the above the only other area would be the oil and oil additives; the only way of establishing this would be to place a new half moon in some oil and keep an eye on it to see if there are any adverse effects.

Kind regards

David

[steveww]

I have seen aluminium half moons advetised. Can't remember who though

[M100]

steveww>I have seen aluminium half moons advetised. Can't remember who though

Not seen them advertised but there are pictures of some on the yahoo groups photo area.

[type26owner]

I kludged together a fitting for the block to head area but I can't remember if I posted that info already. If I didn't it's a rather clever but simple design. I just cutoff the lower male end that sticks into the block. The top of these counterfeit rubber thingie works okay. It's the male part that sticks into the block that swells up and constricts the passageway. Made an aluminum one which is sealed to the block with an o-ring that has a radial interference fit. This has a short male pipe barb to fit snugly fit up into the rubber part. A piece of safety wire provides the clamping force to make that connection oil-tight. There is also a thin flange which keeps the male end from falling through the hole into the block. Best of all it can still be installed or removed without having to remove the head.

[freddy22112211]

Hamish,
I've also had 2 perished (soft, sticky, leaking) oil return tubes in relatively short periods of say 5 years (not so many miles) - I use synthetic oil - perhaps it's that(?)
The half moons also need replacing - but with me they go hard! and seem to shrink.
Gordon

[twincamman]

Hamish I replace the D seals every 50000 miles to 60 000 miles along with the rebuild on my super 7 tc ----they are always hard and as new ----I get them in the rebuild gasket set--they are only a couple of bucks a set ---I use 20 50 Valvoline and no additives[ would you put honey in the crankcase?] most certainly not stp-- or any thing to thicken the oil --its all pixie dust -- ed law

[Hamish Coutts]

Thanks for the comments guys. As helpful and supportive as ever.

Looks like I won't be adding any of Ed's pixie dust to my oil after the rebuild. Does anybody rate that stuff anyway?
I can live with the half moon problem as they are easy to see/inspect and replace. It's still a bummer that they deterioriate, though. Why do people make things that are not fit for purpose?

It's the oil return pipe that's the worry as the hole in it really does close up. Keith - your mod to the oil return pipe sounds mighty fine and I think I can visualise what you are on about. Have you any more info? e.g. a photo.

Regards,

Hamish.

[type26owner]

Hamish,
Here's representation of the oil breather pipe mods. Any machine shop should be able to make you one based on this picture. Just provide them the hole diameter in the block and the new rubber oil breather pipe and this picture.
http://www-eng.lbl.gov/~franck/Car_Stuf ... e_mods.pdf

Only the new latest version of the half-moons are swelling up. You can tell if yours are by looking to see if the outside flat is still flush with the head. When they swell up they move towards the inside of the engine by about 1/8". They would fall in but they rub up against the head of the bolt holding on the camshaft sprockets on the front. In the rear they rub against the pipe plugs in the cams.

[Hamish Coutts]

Thanks Keith. Looks fairly easy to do.

Regards,

Hamish.

[builder618]

Has anyone thought of tapping the holes in block & head and using a fitting to connect to a clamped hose. I have always suspected that connection as a source to lubricate my concrete floor. Hey my concrete never rusts under my elan.

[type26owner]

Hamish,
Once you install an oil breather that scavenges the crankcase efficiently you might notice a new type and quantity of discharge. I have a catch tank so I can tell what's happening. When I did this modification it was mid-winter and the discharge was quite an alarming amount of white emulsified oil and water goo. First thought I my new rebuild of the engine had an internal water leak. Monitored the coolant level carefully and it remained constant. Also did a CO chemical test of the coolant to see if it had a small head gasket leak but that was negative also. The goo turned out to be just the normal amount of water vapor that leaked past the rings along with the blowby and circulated through the engine. That breather mod had really increased the flow and the discharge was breathing in and out at the same rate as the pistons which move quite a bit air around inside the crankcase. That rapid breathing was enough to mix the oil and water in the discharge tubing into a consistancy like that of whipped cream. Once drier weather arrived the goo stopped being discharged. So don't panic when it happens to you too.