Ring gap Help

[elliotaw]

Im just about to assemble the rings and pistons into my engine.

The engine has been bored and honed to 88mm.
The pistons and rings are all new Ross items.

The paperwork that came with the pistons shows some calculations to work out the top and 2nd ring gaps.

It states that the top gap should be bore dia (inches) x .004, and the 2nd ring x .005.

This equates to :- Top ring = 3.464 x 0.004 = 0.014in (14 thou)
2nd ring = 3.464 x 0.005 = 0.017 (17 thou)

I had the machine shop do the ring gaps for me as I assumed they would do a better job than I could.

I've just checked No1 bore and found the ring gaps to be 17 thou for the top ring and 18 thou for the 2nd ring.

I double checked everything and even set the rings into a different bore incase they numbered them differently but the same result.

On calling the machine shop, I explained the problem and the reply was that he had fitted a gazzillion sets of rings and from his experience the gaps were too small so he made them bigger (hmm).
I'm not doubting his experience, but I'm sure Ross wouldnt have pulled these figures from their behind.

What do I do ?

Elliot

 

[cribbj]

Perhaps the machine shop felt for your application a looser gap would work better? Not knowing the details of the application, Ross probably sent their standard "fitting sheet" for the motor.

Why don't you contact Ross, explain your application, and get a 2nd opinion about the gaps the machine shop installed?

 

[Lextreme II]

Elliot,

What is your over bore size? Was that part of the group buy or you order directly yourself? I dont remember the over size we had for the pistons GP. I think it was like .010" over. I dont remember exactly. Anyone remember?

 

[elliotaw]

The pistons I ordered I got myself through Ross. They are standard 10 : 1 ratio.
Diamater +0.5mm to suit a bore of 88mm.

I'll call Ross to ask their advice, I am just not impressed that the machine shop took it apon themselves to decide what I wanted without consulting with me first especially after I explititly asked them to do everything by the numbers and to the specs I supplied.

Elliot

 

[stevechumo]

As a general rule of thumb, a ring gap of .004" is good for most applications, but that still depends. The first and the second gaps should be the same for smooth movement. I haven't tried different gaps in the same cylinder but I think that tiny difference wouldn't make a big deal if you're not going with higher compression or forced induction. Since they're not installed yet, I would ask for a tighter ring set and ask the machine shop to go from there.

 

[elliotaw]

Just got off the phone to Ross in the US. Their technical guy said that 3 thou oversize would be fine and that if the car was going to be used for any kind of racing or fast road use that he would have done the same.

I'm still not convinced...but that's mainly down to lack of experience with engine building. I guess at the end of the day I'm in the hands of the professionals....

I'll check the rest of the gaps with all the bores and assemble the motor if they are all similar.

Elliot

P.S. Stevechumo, ross paperwork explains that the 2nd ring gap should be bigger than the first to allow any leaked gas thats gotten past the top ring to escape rather than trapping it and destroying rings. That info is available on their website....sounds logical I suppose ?

http://www.rosspistons.thinkhost.com/pdf/ross_racing_rings_installation.pdf

 

[stevechumo]

Yes, they have a point there. I think you still need to install the rings based on your need. Is it naturally aspirated or turbocharged? For N/A application, that doesn't really matter. Turbocharged application might need a slightly larger gap on the second ring for the pressure to go past it faster. As I remember correctly when 2 rings have the same gap (I haven't touched any internal engine for 2 years now, except the timing belt, valve covers...etc), the top ring will eventually close more than the second ring, which means the second ring will have a larger gap anyway. However, I would check back with the 1UZFE repair manual for the correct gaps.