I'm having to pull my engine apart due to blow by or a faulty valve stem seal. Since its costing alot to do this i'm going to put in gapless rings and possibly forged pistons.

My question is has anyone used a gapless top ring as opposed to a gapless second? I know that the second is used on a cast piston due to the likelyhood of ringland failure but since the forged ones are stronger should i go for a gapless top or am i going to find that the ringlands break on that after a couple of years?

Phil/Nigel, which ringset did you go for?

No idea what I went for - I just asked Barbz for forged pistons and gapless rings and that's what he supplied

I didn't know there was the option of different ringsets

I've just been reading total seals website. They offer a gapless top or second ring. The gapless top they claim gives around 3-5% more power. (Although this could just be normally aspirated engines).

There is a difference between gapped down rings and gapless.

Ross

Err.. thanks for the statement Ross.

Sorry Ken, same as Nigel, I left Keith to worry about such things !

Phil

Sorry, had wrote a lot more, but was unsure on how accurate it really was.

U know who you should ask!!

Ross

No worries Phil.

Ross - I'll speak to Barbz tomorrow when i go pick up my head.

If you get total seal ring set the compression rings will all be gapless.

And as for "I know that the second is used on a cast piston due to the likelyhood of ringland failure". No that wrong if you're ring lands break (due to detonation I'll add)then its screwed. The top ring does in the region of 70-80% seal, the second ring works exactly the same mopping up most of the remaining seal which is blow by down from the first. Road cars and all but top end race engines will use 2 compression rings.

Ring lands don't break as a 'consumable' item. Forge piston will be much stronger, so less likely to fracture with detonation - but you must avoid it. Dont ever rely on a det sensor to help you out.

rich

I have just recieved a set of gapless top rings after speaking to Barbz about the very same thing. 5 gapless top rings cost 144.19 squid from performance unlimited. Barbz seemed to think that the normal pistons are not too bad. He said to get oversize second rings and get them gaped down to the minimum tolerence. This is what I will be doing very soon.

Sorry Rich, you've lost me with your reply.

I'm not looking for gapless top and second. I wondered if anyone had used the top as opposed to the second (which Barbz tells me is more conventional). I'd be using a standard oil ring and standard compression ring i didn't get gapless.

I was also considering forged pistons as i'd heard instances of cast pistons breaking ringlands (and not only from det). It's basically costing me alot of money to pull the engine apart and i'd rather get it right now then have to go through this all over again in a year. The car will be mapped after the build therefore pretty much ruling out any chances of det.

Stevo - which pistons have you gone for? You're not going to use standard ones are you?

From speaking to Barbz I am using a new normal set of pistons which I got from him. I am in the process of buying a house at the moment so do not have a spare 700 pounds for forged pistons. Barbz seems to think they will be ok. Who is builing your engine Kenno?

Put them on the second and not the first, not sure why you would do that. The better the top seal the lower the over all blow by. Second rings dont often seal that well and the gap isnt the issue, its the lack of pressure behind the ring to push it against the cylinder wall . IN fact blow by is realy more of a low speed problem when there is plenty of time for the gases to leak down through the gaps. At higheer speed 3k+ this really isnt so much of a problem (hence why slow marine diesels have 4 rings).They are expesive for what they are so if cost is an issue which it always is stay with conventional ring design.

I doubt the ring land failure on any 20vt has happened for any other reason then det unless the engine has over rev'd. Det pressure does a good job of pushing the ring lands together, trapping the 2nd/oil rings, fatiguing (sp) the piston, and blowing the edges off the first rings.

Get the forged piston, see if you can use a fiat ring pack or conv supplied ring set. Ok the seal wont be quite as good as gapless, but your talking as good as a new engine.

Rich

I think the Fiat ring sets are at least as expensive as the ring sets usually supplied with forged pistons.

If you go forged pistons then there is also the choice of whether or not to get lateral gas ports.

And if you're investing in fitting forged pistons then fitting forged rods is more or less a zero labour cost job.
Might as well do the job properly if you're going to do it!

Stevo - Rog will be rebuilding my engine. I'm getting him to flex hone the bores then put it all back together.

Thanks for the info Rich. I've now just to see if i've got that £700 lurking around the back of the sofa.

Argh.. John.. No.. I can just about afford the Pistons!!!!

I was going to get JE Pistons with a gapless top ring and use the fiat second and oil ring. Looking to have a reliable engine and run a sensible amount of boost (1.5Bar) with my new flowed head and balanced rods. I'm not looking for mad power, just a good thump of torque and reliablity.

Yeah, you say that now.....

I wish I could find 1200 for forged pistons and rods down the back of my sofa! Oh well. I have rubbed down two alloys tonight for spraying tomorrow. I have not plucked up the courage to start ripping my engine apart yet. Where has Steve from alternative autos been? I have been trying to phone him all day to order up a cambelt and gasket set.

Will be flex honing my bores as well, only looking to run 1.3 bar myself but like you I want it to be reliable.

Matt - Had I bought a paddle clutch it might have been a different story. But I think with a flowed head and slightly more boost i'll be on the limit of the tyres and clutch.

Stevo - who's flex honing your bores? I've found a site which sells hones but they're not cheap.

I am. Yeah looked into it and found a place on ebay that sells them. They are 76 quid ish. Where did you see some Kenno? Think I need a 3 - 3 1/4 with 240 grit....

Yep - GBD 3 1/4" is right with either 320 or 240 Grit. I called the UK distributor and they quoted me £86. I might have also found a cheaper place online (provided it doesn't get any import tax applied to it).

Would you be interested in just buying one and sharing the cost? Rog said that he'd buy the hone from me after i'd used it. £86 for a 5 minute job does sound rather expensive.

Yeah sharing the cost sounds like a good idea. When is your engine being done?

The JE pistons are more performance oriented then reliability oriented. They have a 5 thou clearance which means over time they will wear somewhat.

Honing tool

This is the cheapest I have found, well it is about the only one I have found actually. 76.38. It is at the bottom of the page.

Stevo - not for another month yet. I've still got to decide what i'm doing about pistons. I'll see if i can order the flex hone any cheaper online then PM you with my findings.

John - Does that go for all forged pistons? I was told that the forged pistons required a larger clearance on the basis that they expand.

Well to a certain extent yes. The ones I use have a 3 thou clearance and so have a lower power limit (which is still way beyond what I will ever use). But they will last probably 120-150k miles I would guess. We took them out my car after 20k and they looked fine as did the bores.
The JE ones do have a coated skirt that helps and dampens the rattly noise you would get with some of the other lesser brands.

The greater the clearance the more the wear on the pistons is self-perpetuating BTW

Given the importance of the clearance, it sounds like I should really rebore the block to match a set of pistons. I was hoping that i could simply buy a set of forged ones, flex hone the block and drop them in.

Alas it's not, as mentioned before in previous threads, you get the block to match the pistons, not the other way round