Arias Pistons - Bore size

[campbellju]

This has been an issue since Christmas but thought I'd post for sympathy/ideas. The engine builder measured all the pistons and bored each cylinder 4 thou grater accordingly. Came to build it all over Christmas and found the ring gaps were too large. We assume the wrong ones had come with the piston so sourced some others for another SR20 that were definitely for 87mm pistons. These also didn't work. After much head scratching we double checked everything and the Arias pistons seem to be 3.430 inches rather than 3.425 measured around the wrist pin. I had previously spoken to Arias and quoted the part number so they believe this was a 3.425 but it isn't.

The ring gaps are closer to 40 thou than 20 thou so are too large.

The engine builder is going to go through the parts catalogue and see what he can find from another car engine that would work. plan B is get some custom rings and plan C is try to source yet another block, buy some new pistons and start again. Plan D is burn the thing and throw on some burgers for a BBQ

2 steps forward 3 back.

 

[campbellju]

Not sure if there is a Plan E with 87.5 or 88mm pistons with standard liners?

Edit: At the moment Plan D is favourite so probably need to walk away from the car for a bit.

 

[fubar andy]

Good lord, it's not working out is it?

 

[vpulsar]

How unfortunate Jim, I've built two engines or rather should I say I've had two built for me and I've never come across this problem. But I used HKS pistons in the first and Danny is using CP's this time.

Good luck mate I hope it sorts it's self out, I'd think of just buying some new CP pistons that are known to work and more on with your life.


Rob

 

[PobodY]

Edit: At the moment Plan D is favourite so probably need to walk away from the car for a bit.

This is a feeling I'm familiar with.

At some point I will decide it's all too much effort (and money), but I haven't got there yet. - Maybe if Nissan make that IDx...

 

[red reading]

You could go cp 87.5 mm with an apexi 88mm headgasket to save the block, or just get new rings for what you have , we had the same aggro with stumos pistons and liners and Andy managed to source new rings.

 

[campbellju]

Thanks for the moral support, much appreciated. What ever I do from here it will start costing me more than if I'd just bitten the bullet at the start and bought CP. Stumo will be saying "I told you so" when I next see him.

Danny, thanks for your feedback. It's good to know it's not an uncommon problem. Thinking about it, I will need to check my cosworth HG fits the bores still, I'm not sure how much leeway there is on the 87mm?

It seems like sourcing new rings is the route through this. Not ideal but hopefully it is the path of least resistance.

 

[Fusion Ed]

Usually I'd recommend you use pistons that the machine shop has a lot of experience with. It can save all the trouble like this. If it helps I build my SR20s when using Mahle 4032 grade (which I spec up to 450hp) I will give them 17 top ring 18-20 second ring and oil of 22.

I'm yet to have a problem which is nice as I'm responsible for mapping too!!

 

[STU666V]

Just buy my spare forged engine and bolt it in

You can pay it up so the wife doesn't know ;-)

 

[campbellju]

Thanks for your thoughts Ed, the ring gaps seem similar to what I'd planned. Oil gap is different but so are the pistons.

@Stu, you never know but for the moment I will persevere.

 

[Fusion Ed]

The oil gap doesn't matter half as much really. The tolerance on them is quite large.

 

[red reading]

I run 18 top 22 middle and 15 oil on cp pistons

 

[Slunch]

Bad luck and very frustrating. I'd almost say don't get too hung up on it. The chap who built my engine started talking about ring gaps, and I told him to trust HKS, stop bleating and jam the pistons in the damn holes, he looked at me like I was from another planet and got on with it. Found out how potentially catastrophic that could have been later on from Pulsar Bob. But last time I checked I was holding 150 psi on 1 and 149 on 2-3.

 

[campbellju]

Saw my engine builder this morning. We'll try to source a set of rings from 2.2l Nissan Z engine with 1 size overbore. These will be 87.5mm rather than 87.05mm so we will have to see how they fit.

I also took the Cosworth head gasket in to see how it fits on the bores. Without measuring it seems proud of the bore by 0.02mm which tells you Cosworth have no problems with their quality control! Would need to do a trial build to see if this matters. I'll start looking at HG options again just in case.

 

[Slunch]

Good to hear this is moving forward, hope it works out. I may look into getting a cosworth he to replace my hks when I come to it.

 

[campbellju]

Thanks slunch.

 

[campbellju]

Just had an idea about the HG. The Cossie one I have might be too small for the bore. If I can get these 87.5mm rings to work then an option might be a 2.0mm HKS HG. For pistons correctly sized these leave too much of a lip but for these crappy arias pistons they might be better. I've done a quick search on the internet and can't seem to find somewhere obvious that still sells them.

I did find the Tomei 88m gasket at a good price so that might still be an option if these rings are no good.

 

[vpulsar]

I fitted a 2.0 mm HKS head gasket to my very first pulsar when the standard one went and the car was horrible to drive afterwards, Just didn't drive as nice off boost at all.



Rob

 

[Slunch]

I've got a 1.2mm 87mm HKS that I'm thinking of swopping for a cosworth. Dunno if it's any good to you, it's still on my car at the min.

 

[red reading]

Tomei is a similar/ same design as cosworth jim and is 88mm which would be ok on your engine, hks I have seen as large as 89mm which is a bit of an issue and I think maybe a tolerance problem in manufacture.

and thickness lads is decided by how much you skim off the deck, I order headgaskets when the bock is built as the crank throw and rod lengths dictate if the piston protrudes from the block or not as well .