# crank and rods clearance piston ring gap??



## DrGtr (Jul 18, 2009)

planing to start building the super powerful  rb28 tomorrow i know that i should have a bit more clearance than nissan recommends for a high revving engine, i will be using acl race bearings and plastigage what clearances should i have for the crank and what for the rods and what about the cp piston ring gap??


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## R32 Combat (Jan 29, 2004)

What size of ACL bearings are you selecting?

Also, whats your PBC?


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## adamsaiyad (Aug 23, 2006)

if you read the build post i made that will give you some insight, also one of tyndago's posts on his site also mentions clearance.
If im not mistaken if you using a aftermarket pump the clearance on mains and big ends needs to be more in the middle of the nissan called for specs 0.050mm i think .... correct me if im wrong as the small end is like .030mm and big side 0.090mm max clearance...
The cranks need room to flex .


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## adamsaiyad (Aug 23, 2006)

as for ring gaps depends on pistons you using as each manufacturer has their own settings they use ..


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## DrGtr (Jul 18, 2009)

Standard size acl.what is PBC??
Oil pump is tomei. Pistons I think it should be 14 thou??
Cp 87mm.


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## adamsaiyad (Aug 23, 2006)

follow Cp specs for ring gaps .
For bearings if they are standard on a new crank clearance might be a little small on the tighter side not good, but if a second hand crank polished then i think you will be good to go .... i have used standard acl race bearings with the X denotiing extra oil clearance 0.0001" extra


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## GT-R Glenn (Nov 9, 2002)

Wow, a tenth of a thou ....


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## R.I.P.S NZ (May 7, 2004)

GT-R Glenn said:


> Wow, a tenth of a thou ....


Was thinking exactly the same thing opcorn:


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## R32 Combat (Jan 29, 2004)

2.5 microns is a days march here.


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## DrGtr (Jul 18, 2009)

as i have checked with cp pistons when bored correctly i think the rings should not need anything they dont even write about the rings in the diagram, in nissan manual for the crank is up to 0.040?? for high revs 0.040-0.050 is good??


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## R.I.P.S NZ (May 7, 2004)

DrGtr said:


> as i have checked with cp pistons when bored correctly i think the rings should not need anything


Just so I'm clear, you intend to install them as they are straight out of the box?


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## DrGtr (Jul 18, 2009)

R.I.P.S NZ said:


> Just so I'm clear, you intend to install them as they are straight out of the box?


no just to be sure i will insert the rings in the block and measure the clearance with the filer.is 0.012-0.014 ok ?


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## GT-R Glenn (Nov 9, 2002)

4 thou (.004") per inch of bore size


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## R.I.P.S NZ (May 7, 2004)

2 of the rings on each piston run different gaps and the other 2 run a different gap to the first 2.

The gaps you give are based on ring type, bore size and engine application, fuel used, boost, NOS, no NOS, quick bursts or sustained etc.

There simply is no set gap for every ring in every RB.

Rob


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## R.I.P.S NZ (May 7, 2004)

2 of the rings on each piston run different gaps and the other 2 run a different gap to the first 2.

The gaps you give are based on ring type, bore size and engine application, fuel used, boost, NOS, no NOS, quick bursts or sustained etc.

There simply is no set gap for every ring in every RB.

Rob


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## DrGtr (Jul 18, 2009)

R.I.P.S NZ said:


> 2 of the rings on each piston run different gaps and the other 2 run a different gap to the first 2.
> 
> The gaps you give are based on ring type, bore size and engine application, fuel used, boost, NOS, no NOS, quick bursts or sustained etc.
> 
> ...


ring type are the stock of cp, piston size 87mm, application is time attack some times, engine rev limit 9000rpm. what would you recomend for this application?? is 4 thou (.004") per inch of bore size as my friend Glenn posted good enough for this application?


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## R.I.P.S NZ (May 7, 2004)

Your missing something here, there are 4 rings that need gapping per cylinder, 2 are the same, the other 2 and their required gaps are both different to the first 2.

87mm = 3.425in 4 thou x 3.425 = 13.7 thou, so which ring/s are you talking about giving 14 thou?

I can't reccommend what might be right for your motor sorry, there's way to many variables.

Rob


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## DrGtr (Jul 18, 2009)

R.I.P.S NZ said:


> Your missing something here, there are 4 rings that need gapping per cylinder, 2 are the same, the other 2 and their required gaps are both different to the first 2.
> 
> 87mm = 3.425in 4 thou x 3.425 = 13.7 thou, so which ring/s are you talking about giving 14 thou?
> 
> ...


14 thou i am talking for the first ring.


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## GT-R Glenn (Nov 9, 2002)

Rob, its a pretty basic engine 700hp type of thing
I would think 14 thou would be spot on for ALL the rings / if they are conventional type


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## DrGtr (Jul 18, 2009)

GT-R Glenn said:


> Rob, its a pretty basic engine 700hp type of thing
> I would think 14 thou would be spot on for ALL the rings / if they are conventional type


second ring has bigger distance i think, what do you mean basic engine mate??


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## DrGtr (Jul 18, 2009)

the machine shop told me that the cp piston rings dont need cutting , then i was ready to put the rings to the pistons and before i have done this i went to check with my filler the rings in the bores of the cylinder, and found out that the first ring have almost no clearance and the second one have only 013 i should be very careful and triple check everything since the head job i had, on Tuesday i will torque the torque plate i have made and measure all the bores 3 times in all the positions , then the pistons size and see what clearances have made to my cylinders it should be 3.425 bore size and then if everything is ok i will make the top ring 017 second 021 and bottom 015 will this be ok?


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## R.I.P.S NZ (May 7, 2004)

DrGtr said:


> the machine shop told me that the cp piston rings dont need cutting




I've never had a set of CP rings that were ready to go out of the packet.

The gaps you have should be fine and you should be looking to see around 0.003" piston to bore clearance.

Rob


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## DrGtr (Jul 18, 2009)

R.I.P.S NZ said:


> I've never had a set of CP rings that were ready to go out of the packet.
> 
> The gaps you have should be fine and you should be looking to see around 0.003" piston to bore clearance.
> 
> Rob


i dont understand it should be fine to have top ring almost no clearance with the second one to 013?? this is what i have now.
or you mean is good to cut the rings to 
top ring 017 second 021 and bottom 015 would it be better to make the bottom 016? or it will be no big difference, rob to what clearances you cut the cp rings 87mm to the engines you sell for 9000rpm time attack cars?


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## R.I.P.S NZ (May 7, 2004)

DrGtr said:


> i will make the top ring 017 second 021 and bottom 015 will this be ok?


This should be OK but seeing as you are going to gap them you might not need to go quite as big but there are alot of variables as I have said previously.

Good luck :thumbsup:


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## DrGtr (Jul 18, 2009)

R.I.P.S NZ said:


> This should be OK but seeing as you are going to gap them you might not need to go quite as big but there are alot of variables as I have said previously.
> 
> Good luck :thumbsup:


thanks for your reply, if i go tighter you think it will be better ? for example
top 016 middle 020 and 015 or you prefare the previews combination? and the crank /rods at 050 will be too much? farndon crank and rods sorry for being asking all these but its my first high performance engine and i am trying to learn from you who made all these combinations.


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## R.I.P.S NZ (May 7, 2004)

as I have said there is no set answer, there's alot of variables but for what I "think" your doing those gaps are probably on the lose side.

Rob


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## DrGtr (Jul 18, 2009)

with out wanting to make you responsible but as an example what clearances you where going to set?


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## DrGtr (Jul 18, 2009)

Just checked the bottom rings they are 021 so is it still ok to use first 016 or 017 and second 020 or 021?


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## DrGtr (Jul 18, 2009)

final cut of the rings and triple checked top 016(017)tight, second 020(021) tight, oil rings 015 ( 016) tight ,i was wrong for the 020 on last time.
cylinder bore checked is 3.4255 clearance of piston 0.0035.


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## DrGtr (Jul 18, 2009)

2 shims set out of 3 to the tomei oil pump, if my sensor is reading well with motul 15w40 mineral oil cold start is 5 bars and warm 3.5-4 bars to the 950rpm.
when i break in the car motul 300v 15w50 will be the oil i am putting


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## DrGtr (Jul 18, 2009)

cold start with the 15w40 is 3 bars at 950rpm and stays like this when warm up i will check again tomorrow morning to be sure can this be normal? or shall i put 10w50 mineral instead?


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## zimnismoboy34 (Apr 18, 2012)

are you running in the engine or have you run it in already ?
Remember a basic basic oil is what you need to run in the motor and get the rings to bed in ?


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## DrGtr (Jul 18, 2009)

i am running in the engine i have put just 200 miles.


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## DrGtr (Jul 18, 2009)

cold start is 3 bars and then it goes down to 2 bars at 950rpm temperature is 40+Celsius with 15w40 mineral motul.


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