18 thou ring gap too much ?

[Exminiman]

Appreciate some opinions,

Just gapping rings on some Calver big bore plus 40 pistons, newly bored block, getting 18 thou gap

Considering Calver pistons are supposed to be able to cope with less clearance, this seems on high side to me.

Is it too high ?

[Herbert]

Far too high! SHould be 6-8 thou

[Exminiman]

I thought rule of thumb was 5 thou per inch, so about 15 thou ?

[Dearg1275]

BMC/BL workshop manual says 0.008 to 0.013 in for standard pistons in standard bore for “S”.

D

[whistler]

You need to contact Keith Calver about this. Email him, he has helped me enormously with my recent 1098 +100 build with his pistons.

[Exminiman]

You need to contact Keith Calver about this. Email him, he has helped me enormously with my recent 1098 +100 build with his pistons.

Good idea, will ping him an email in a moment,
Did wonder about getting plus 60 rings and filing down....

[Exminiman]

Quick update, got an immediate response from Keith, very helpful and now resolved.

18 thou, is OK for my application, happy days

[Hipwell]

Out of spec in my opinion. Might be fine, is 30 thou fine too?

[abs]

I have had a couple of sets of quality brand rings that were in the mid .020"s and that was with piston to bore clearance on the tight side.
It does make me wonder if i`m the unluckiest bloke ever or is everything crap these days

[btetley]

On my pistons from Calver the info sheet said some pistons come with 20 thou and that this was ok even though the recommended was about 12 from memory.

[Exminiman]

On my pistons from Calver the info sheet said some pistons come with 20 thou and that this was ok even though the recommended was about 12 from memory.

This is pretty much where i got with it, it seems that some thinking has changed away from the tighter the better ( ooh err misses ) - this seems to be based around test data from AE Hepolite( before they were bought out) and current manufacturer, showing that up to about 40 thou, there is no meaningful loss of power. There is a potential benefit in not getting broken rings or affecting the ring lands - which may be why some manufacturers are specifying larger ring gaps....?

Tried to get a bit more back ground and this post is quit interesting as it debates both sides of the argument.
https://www.speed-talk.com/forum/viewtopic.php?t=30376

[Exminiman]

On my pistons from Calver the info sheet said some pistons come with 20 thou and that this was ok even though the recommended was about 12 from memory.

This is pretty much where i got with it, it seems that some thinking has changed away from the tighter the better ( ooh err misses ) - this seems to be based around test data from AE Hepolite( before they were bought out) and current manufacturer, showing that up to about 40 thou, there is no meaningful loss of power. There is a potential benefit in not getting broken rings or affecting the ring lands - which may be why some manufacturers are specifying larger ring gaps....?

Tried to get a bit more back ground and this post is quite interesting as it debates both sides of the argument.

https://www.speed-talk.com/forum/viewtopic.php?t=184

Edit, linked to wrong thread now changed

[Spider]

Better a bigger gap is safer than one that's too small.

I've run gaps (on 1275 engines) up to 26 thou, but more routinely around 22, there's quite a bit to take in to account when settling on a ring gap, it, how thick the rings are, what they are made from, how far down from the crown the top ring is, bore finish, N/A or boosted, types of fuel and on it goes.

I have been trying to lay my hands on a back to back dyno report that actually found - to a point - wider gapping was better for power and sealing than 'standard' gapping and it did go in to some of the reasons why.

With the (seemingly) larger gaps that I have run, I've never found any down side what so ever.

The gaps that are stated in the workshop manual are only a guide for the factory pistons and rings, of which those types (which used imperial rings) have been NLA for a long time now and so these figures have no relevance and shouldn't be used. If in doubt, follow the actual Piston and Ring Manufacturer's advice, not that from the workshop manual.

[Exminiman]

just realised I linked to wrong thread above, have now changed !

[Exminiman]

just realised I linked to wrong thread above, have now changed !

interesting post towards end of thread about using a torque plate before checking ring gaps..... anal or not ?

[Hipwell]

just realised I linked to wrong thread above, have now changed !

interesting post towards end of thread about using a torque plate before checking ring gaps..... anal or not ?

Nope, in the states the top engine builders will use a torque plate to hone the cylinder and heat the block up to represent running conditions, trying to get someone in the UK to do it seems impossible, does it make a difference, who knows but I can't hurt.

Shooter

They are often referring to building engines with overbored original blocks with wafer thin decks and bores or terrible quality after market blocks. Those American forums are full of over anal on detail and then thick as cheese with the practicality of actually building the engines. If your on Instagram, look up the account steeldustmachine, he's a skilled engine machinist and shows the shortcomings of American V8's, and the quality of engines that come out of their 'shops'.

TBH I don't get why people building A-series engines all day long don't use them(torque plates) but with FIA engines now way over 100BHP per litre, I guess they would say why bother and 60yo classics burning a bit of oil used a handful of times a year, who cares.


Going back to the ring gaps, are you all building race engines or road engines where you want good oil retention, no smoking and long service life? The second ring is mainly there for oil control, there is Mini race engine builder I know with his own two ring piston, its not there for power, so ring gap is irrelevant for power, more critical for oil.

A good guide I use...

http://npramerica.com/attachement/Introduction1.pdf

The Nippon rings are used on the Omega's offered for Mini's that offer good power, service life and oil control when used on the road and track.

Talking racing, I have data sheets for some WRC engines in the early 2000's, Subaru were down to 9 thou ring gaps on 92mm bores running big boost and anti lag etc.