Discussion
I'm just checking the ring gaps as I reassemble my AJP V8 (TVR) engine. The build manual suggests that the top ring should have a gap of between 15-17 thou and the second ring should be 9-11 thou.
Measuring the (new AE) rings in the checked bores the top rings are all around 17 thou - OK, however, the second rings are all around 14-15 thou.
Having done a bit of research on this it appears that there is a suggestion that the second ring gap should be bigger than the top ring to prevent piston ring fluttering. I have also come across a "calculator" which suggests that piston ring gap should be calculated as bore (inches) X 0.0045 (top ring) or 0.0055 (second ring). This would give me gaps of 16 and 19 thou respectively.
So - what should I do - leave them as they are, try to get another set of second rings to achieve the TVR guidance or open them up as per the "formula" above?
Any thoughts welcomed!
Also posted on the Cerbera forum.
Measuring the (new AE) rings in the checked bores the top rings are all around 17 thou - OK, however, the second rings are all around 14-15 thou.
Having done a bit of research on this it appears that there is a suggestion that the second ring gap should be bigger than the top ring to prevent piston ring fluttering. I have also come across a "calculator" which suggests that piston ring gap should be calculated as bore (inches) X 0.0045 (top ring) or 0.0055 (second ring). This would give me gaps of 16 and 19 thou respectively.
So - what should I do - leave them as they are, try to get another set of second rings to achieve the TVR guidance or open them up as per the "formula" above?
Any thoughts welcomed!
Also posted on the Cerbera forum.
Edited by itiejim on Sunday 24th January 11:49
I always use file fit rings and gap to the tightest recommended SAE tolerence.
"I have also come across a "calculator" which suggests that piston ring gap should be calculated as bore (inches) X 0.0045 (top ring) or 0.0055 (second ring). This would give me gaps of 16 and 19 thou respectively"
"I have also come across a "calculator" which suggests that piston ring gap should be calculated as bore (inches) X 0.0045 (top ring) or 0.0055 (second ring). This would give me gaps of 16 and 19 thou respectively"
There is no such thing as a random calculator. Use manufacturers specs where possible.
Although unless the gaps were huge, I wouldnt worry too much sleep over it.
If they are tight on the other hand, file to ensure there is sufficient gap. I'd rather a little blowby than a ring sized in the bore.
Although unless the gaps were huge, I wouldnt worry too much sleep over it.
If they are tight on the other hand, file to ensure there is sufficient gap. I'd rather a little blowby than a ring sized in the bore.
itiejim said:
TVR spec 15-17 thou top ring and 9-11 thou for the second ring.
I'll have 17 top and 14 second.
I was a little concerned that 9 thou was very tight anyway. So... fit as is?
Ive no idea if 9 thous is tight or not. That would depend on the usage, and manufacturers spec for the rings for that usage.I'll have 17 top and 14 second.
I was a little concerned that 9 thou was very tight anyway. So... fit as is?
If the specs you give are accurate and relevent to your application, then I wouldnt be too worried about the gap being slightly bigger.
The AE ring gaps look fine to me. The OE spec on the second ring looks very tight though and I'd have my reservations about going that low. From the point of view of heat expansion and ring end butting the second ring gap certainly doesn't need to be as wide as the top one. However the alternative theory about using a wider 2nd gap than the top one to let pressure that gets past the top ring escape rather than build up above the 2nd ring is more applicable when you get to engines with really serious compression ratios or forced induction or very high specific outputs per litre. With all due respect a cooking two valve per pot engine like yours ain't really pushing that envelope.
In any case you're talking miniscule changes in power output as the ring gaps vary a bit. On an 8 litre drag race Chevy putting out over 1000 bhp on a compression ratio and internal loadings that mean everything is on the bitter edge of blowing up sure you'll see 5 or 10 bhp if you get the ring gaps absolutely optimised to the thou but on smaller lower tuned engines the power change just disappears into the white noise of consecutive dyno runs.
The main impact of ring gaps is actually on emissions which is why OE manufacturers are going really tight on them on road cars to cut down the crevice volumes which hold gases that never get burned properly. This mainly applies to the top ring though. I've seen 12 thou or less on similar bore sizes in recent years such as the Ford Zetec for example.
AE always play a little on the safe side on ring gaps and personally I've never been able to spot any adverse impact on the way the engines perform. Stick em in as is and spend your time worrying about more important things like if you use a different colour paint on the sump might it radiate a couple more millijoules of heat away.
In any case you're talking miniscule changes in power output as the ring gaps vary a bit. On an 8 litre drag race Chevy putting out over 1000 bhp on a compression ratio and internal loadings that mean everything is on the bitter edge of blowing up sure you'll see 5 or 10 bhp if you get the ring gaps absolutely optimised to the thou but on smaller lower tuned engines the power change just disappears into the white noise of consecutive dyno runs.
The main impact of ring gaps is actually on emissions which is why OE manufacturers are going really tight on them on road cars to cut down the crevice volumes which hold gases that never get burned properly. This mainly applies to the top ring though. I've seen 12 thou or less on similar bore sizes in recent years such as the Ford Zetec for example.
AE always play a little on the safe side on ring gaps and personally I've never been able to spot any adverse impact on the way the engines perform. Stick em in as is and spend your time worrying about more important things like if you use a different colour paint on the sump might it radiate a couple more millijoules of heat away.
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