Is my block o-ringed???

[Datman]

Hi guys,

I recently stripped down my FJ20T for a rebuild, which is coming together nicely. One thing I am not 100% sure of is the top of each cylinder bore.

The top of each bore has had a step machined into it, and a ring fitted to this step. the head gasket, does not have a metal ring in place for each cylinder. The ring that sits in the groove is also slightly bigger than the bore itself. The ring is 91mm ID, and the bore is 90mm. There is no corresponding groove in the head.

My thoughts on O-ringed blocks, was a small groove not connected to the bores, with a thin piece of wire inserted. Is this another method of o-ringing?

Pics of the metal rings can be seen on my web site http://www.angelfire.com/retro/mpamo...ts/sunnydiary4 scroll to the bottom and you will see the rings in front of the Pistons.

Can anyone tell me what this set-up is all about?

Cheers,

Mark.

[psi999]

Hey dude i'm not too sure what your asking but this is a picture of what an o-ringed block looks like.....



a grove is cut into the block and filled with a thin piece of wire

I have never heard of anything like what is done to your engine.

Hope this helps you out

Jon.

[Datman]

In your picture, it looks as though, the groove is set back from the bore - is that right? That is what I understood O-ringed blocks to be...... just trying to figure out what mine is, and if there is anything I should know prior to re-assembly.

Thanks for your input dude.

[Datman]

Mystery uncovered!

Ok found the answer I was looking for....... For anyone who is interested....

The rings are a sealing ring for each cylinder. They are made of brass and fit into the machined recess on the top of each cylinder bore. These rings sit approx .050" proud of the block, and seal the cylinder to the head. The head gasket is then modified, basically the sealing ring in the head gasket is cut out and then installed as per normal.

So now I have something else to check.... I need to measure how far the sealing rings proturude from the surface of the block, and then make sure the headgasket is the correct thickness to suit! Add this to having to learn how to set Cam timing (due to the adjustable cam wheels) and this simple little rebuild is turing into a very steep learning curve!

Who said the FJ20 was an easy engine to build? (Well they are when they are standard )

[thehelix112]

Interesting stuff. Can't see any advantage to it beyond o-ringing as now you potentially have these rings running straight into the head and limited crush/sealing everywhere else! So you need the gasket crush thickness to be precisely identical to the height of these rings. :S

Wonder why the builder didn't just O/W ring it and be done?

Dave

[Datman]

Very good question Dave, and your exactly right. Now I need to get a new head gasket, measure the thickness, then measure the sealing rings and the recess to make sure everything matches up. If it doesn't (and I bet it wont ) then I have to have new sealing rings made too.

Something I thought would be so simply is turning into a major project!

[Nero]

Spesso gaskets do this for their competition gaskets, its more foolproof
The 'o' ringing requires good machining and build. A 968 porsche I saw recently had this stuffed up and gave lots of problems ending in 3 bent argo rods, warped block and head and a full engine rebuild

[Datman]

Thanks dude

Thanks Nero, nice to hear some positive feedback.

I have done some measuring tonight, the brass rings do indeed sit 0.050" above the deck of the block. I also measured the head gasket that I pulled off the head. It meaures.....0.050" Imagine that!

The brass rings are all in good condition, so should not need replacing. It's just a matter of finding a suitable head gasket now....hoping Stew Wilkins can help me out there...I know he has some ACL gaskets made to suit this purpose, just hope the thickness is suitable.

I took some pics of the block and the block with the brass sealing rings fitted, if your interested have a look http://www.angelfire.com/retro/mpamo...ts/sunnydiary4

Thanks guys.

[proengines]

the setup you've got works really well, the rings seal the compression and a composite gasket seals up the water and oil. I machined a 2L Fiat rally engine a couple of weeks ago for a similar setup but it used stainless rings with two sharp ridges running around each ring to bite into the head. The rings were shaped sort of like:
(cross section of ring)

_/\/\_
l____l

(excuse the rough art work)

The rings sit into a machined counterbore in the top of the bore and protrude .005" more than the thickness of the gasket. He used the original stype head gasket but had a hole punch made up the same size as the outside of the rings to cut the fire ring out of the composite head gasket, its used in a press and does a very tidy job. It works brilliantly and eliminates any chance of water seepage.

If your rings are the same thickness as the gasket it should work fine as the gasket will compress a lot easier than the rings and provide a very positive seal as long as the head and block are both dead straight.

I normally use the regular method of a .015" protruding wire o-ring and cut a .008" reciever groove in the head with a copper gasket and threebond 1211 to seal the water and oil and havent had a problem with this either, but theres always more than one way to do things and no particular way is the best or only method to use!


The Fiat is running in Rally Melbourne this weekend so it will be interesting to see how it goes, it's been running in the top 20-30 outright in the ARC with no turbos or 4WD. It's a white/green/red Fiat Abarth, anyone watching the rally keep an eye on it, it's an awesome little car.

[Datman]

Thanks Pro engines,

Should I get a gasket which is slightly thinner than the amount the rings protrude from the block?

Example..... rings protrude 0.050", should I uses a gasket say at 0.045". Or is it better to go slightly over, as the gasket will crush more when the head is torqued. I want to make sure the oil and water galleries seal properly, as well as the cylinders.

Cheers,

Mark

[Nero]

its a good question for pro engines. My understanding is that the rest of the gasket has about .020 of possible crush as the fire rings are usually the critical crush element naturally enough. The Spesso gaskets have removable SS fire rings and the rest is a kevlar material. They are reputedly reusable....never seen one in the flesh so to speak.
Proeng...I saw the fiat in ARN, looks a nice, classic style

[proengines]

Spot on Nero, as long as there is around .020" or so crush on the gasket it should seal fine, the most it will be sealing is 60-70psi of oil and 15-20psi water pressure.

A lot of the big diesels like cummins etc.. run a solid steel gasket that seals between the fire ring on the top of the liner and the head, this is the only place the gasket has any crush, the rest of the holes are all sealed with rubber o-rings that are retained in the gasket.

[Datman]

So my sealing rings protrude by 0.050", therefore the gasket should be 0.70" thick? Did I understand you correctly?

Cheers,

Mark.

[Nero]

believe so. If it were less perhaps a mastic/sealant of some sort would help (spray on stuff not silicone)

[Nafe]

The Fiat is running in Rally Melbourne this weekend so it will be interesting to see how it goes, it's been running in the top 20-30 outright in the ARC with no turbos or 4WD. It's a white/green/red Fiat Abarth, anyone watching the rally keep an eye on it, it's an awesome little car.

I saw it at the Premier State Rally....the 131 Abarth, right?
I can't wait to see it when it's got the full-bore 16v Abarth engine in it....