[engine_work] 2.2 Gti6 Engine Build

[kyepan 291]

rings will blow by until they get a good seal though no?

[Mad Scientist 106]

I've calmed down enough to update this now!

 

Whilst we had only run for about 20 minutes, the ammont of pressure suggested there was issues. John Read was there, and he hadnt seen that much pressure before. That was enough for alarm bells to ring. For the sake of a couple of weeks, and given the money invested, it seemed prudent to pull the head off and see what's happening.

 

Sandy and I have since discussed things more, and we wouldn't be surprised if the problem lies with the total seal rings. (Miles referred to these as total lack of seal earlier in the thread!)

Apparently, John has only seen them used once before, in an atmo cossie, which refused to seal. In the end, they had to spray jiff down the inlet, and it still wasn't right. It's all theory at the moment, but it sounds like they are a bit hard.

 

The good news is, the extra time afforded from this issue has given me time to get other details with the car 100%.

 

I'll put some pictorial updates up soon.

 

[Sandy 189]

A certain fella tucking in to Cap'n Jasper's finest, Cheddar Porker with Chilli!

 

[kyepan 291]

keep going, you'll get there, smart that you stopped and investigated!

[Mad Scientist 106]

I look boss eyed on that photo! Must have been tired!

 

[marksorrento205 80]

Belting food at Cap'n Jasper's Looking forward to a return!

[Sandy 189]

My phone/camera I think!

[alexcrosse 124]

What Ra did you do the head surface for the MLS gasket out of interest? you mention it was very fine. Only just read through this, great looking build so far.

[Mad Scientist 106]

Sandy will have to answer that. Part of the black magic I still don't (need to) know! I know it was finer than SRD originally did it to.

[Sandy 189]

LoL, not something I measure, visual judgement. I know when it's how I want it.

[Miles 331 1 Cars]

Pain in the arse, Keep us posted about the ring's as I know as said quite a few people I know will not use them

[16v205 9]

That's some bad luck, I hope you get I sorted out soon.

 

Ive also not heard good things about total seal rings, going back a few years but the company I got my pistons from build r5 turbo engines and they won't use them gapless rings at all.

 

Rich

[kyepan 291]

Sandy and I have since discussed things more, and we wouldn't be surprised if the problem lies with the total seal rings. (Miles referred to these as total lack of seal earlier in the thread!)

Apparently, John has only seen them used once before, in an atmo cossie, which refused to seal. In the end, they had to spray jiff down the inlet, and it still wasn't right. It's all theory at the moment, but it sounds like they are a bit hard.

 

I would be interested to understand why the rings are not sealing if they are the issue, because it was my understanding that the force of the gas behind the ring is what seals it, rather than the outward pressure of the ring itself (broadly speaking). So that would lead to the assumption that the gas is not getting behind the ring forcing it against the walls of the bore. There should be a gap above the ring to allow the gas to enter and get behind the ring. Sorry if this comes across as a pick, it's not at all, but were the height of the rings and the height of the ring slots (lands?) checked to ensure there was sufficient gap?

 

 

I guess if you add after market pistons, after market rings together the potential for combined tolerances is greater than standard pattern parts, that can be thrown together without these extra additional checks.

 

Cheers

J

Edited August 28, 2012 by kyepan

[dcc 855]

is it not because they are gapless rings?

[kyepan 291]

If I understand the diagram for them correctly, they have a rail which partially blocks the usual ring gap, but still allows gas to enter behind the ring. Above the ring should be an average 0.05mm gap around the circumference of the piston. So that means, 270mm circumference on an 86mm piston, so a surface area of roughly 13mm square that should allow gas to pass behind the ring and push it outwards against the wall. I'm not sure what kind of cylinder pressure is experienced when combustion, but you can imagine if the gap above the ring isn't there, then it's going to be hard for the gas to get behind the ring and pressurise the ring against the wall. I'm not knocking the ring design, just asking if the ring height was checked against it's groove.

 

I would imagine the back clearance is just as, if not more crucial to ring seal, because it would be more responsible for allowing a cavity in which pressure could build, and then act outwards upon the ring.

 

J

Edited August 28, 2012 by kyepan

[Mad Scientist 106]

Good points made above.

 

I had the rings gapped for me by the engine builder who bored and decked the block. I did is more to save me some time and latex gloves than anything else!

 

They ended up having to machine a groove into an old piston in order to gap the rail because they are so flimsy.

 

I also dummy built the engine twice. During this stage I measured everything, including side clearance, back clearance and end gaps. Side clearance was actually tight, but just within JE pistons and Total Seal spec. IIRC it was 0.0015 on the top ring and rail.

 

The issue that we thought about with ring seal is because all rings take some "bedding in" as you know. This is to take any machining high spots off the cyclinder as well as mate the cylinder wall and rings, creating a uniform "seal". Sandy told me this takes about 20 mins on the dyno usually. The theory is that because the chromed top rings are so hard, they don't bed in easily.

 

It's all speculation though until the head comes off, and I don't know when Sandy will get onto it yet.

 

 

[kyepan 291]

Sounds like you did it property, I am also eger to find out why this isn't sealing. Interesting, but more importantly superbly frustrating considering you didn't mess about, and did it by the book. Do you know when sandy is going to pull it apart?

Edited August 28, 2012 by kyepan

[Mad Scientist 106]

Hopefully soon, but I know he needs to get Colin's car and some other jobs finished first.

[Sandy 189]

Yeah, soon. I'm being screamed at by a couple customers, so I have to respect running order a bit.

[Mad Scientist 106]

No rush. I'm happy sorting the other stuff I rushed!

[Mad Scientist 106]

News from Cornwall Land today............

 

Sandy has opened her up (ooh err) and thinks he can see the issue. Its fairly simple to be honest..................

 

But that's all the info i'm giving away for now, just incase! Sandy needs to get it back together and on the dyno first....................

 

One thing I will reveal is that whilst the sump is off, Sandy has recommended changing the ARP2000 rod bolts for Carillos, since they are much safer at higher revs. (8000 plus). Got these ordered today, along with the other bits Sandy needs.

 

Feeling like there is light at the end of this tunnel again today................

 

[welshpug 1,622]

yay!

[marksorrento205 80]

It was music to my ears this afternoon! Already thinking of them pasties

[ginge191 10]

...is this still alive?

 

Just read this from page 1 - incredible!

[Mad Scientist 106]

Won't be long now! Big update soon.