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Discussion Starter · #1 ·
I need advice on my choice of rod bearings for my DOHC ZC boosted engine build

First of all I know I'm supposed to get OEM color coded bearings to get exactly what I want for clearance, but I'm in South Africa and getting OEM bearings is a bit of a nightmare

So I got ACL race rod bearings from the US and plastiguaged them. I get 0.038mm (0.0015") which is within service limit (low limit, nice for standard build)

The thing is that I'm building a boosted engine and have seen on the forums that you should go bigger clearance for boosted engine

I'm looking for maximum 400 Hp but most likely only do max of 300 Hp because of the difficulty finding spares in SA so don't want to split my tranny open with too much Hp or stuff up my super rare EF7 JDM Rex (rare in SA)

Which of the following three options is recommended:

1) Keep it as it is on 0.0015 which is at the bottom of service limit
2) Get ACL 0.001 extra clearance which will bring the clearance to 0.0015 + 0.001 = 0.0025 which is out of service limit, but loose for boost
3) Keep the STD bearing and have the crank polished down 0.0004" which would give me 0.0015 + 0.0004 = 0.0019 which is on max service limit
I know about dangers of crank polish (must be done counter clock and not too much to remove nitrated coating)

The car will be used for regular driving and maybe a couple times a month on a quarter mile pull for fun days at the drags (not trying to break any records)

Trying to keep the build safe because of difficulty getting parts in SA and not able to overhaul the engine every second week!

What I have so far for the rest of the engine build, all imported from Race Engineering in the US:

Eagle rods
Wiseco pistons 9.0:1 special from Race Engineering for ZC engine (75,5mm)
ACL race STD rod and main bearings
ARP head studs
Cometinc MLS head gasket

Finally I had Darton flanged dry sleeves fitted (which would have to be another thread, because I may have screwed up a bit on my block notching!!! So pissed off!!!)
 

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Discussion Starter · #3 ·
The mains with ACL std Race bearings plastiguaged 0.002" so it's at the top end of service limit and I think loose enough for boost?

If I had to make that looser, I'd have to polish the crank a bit, because ACL 0.001 extra clearance would make it very big
 

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Discussion Starter · #5 ·
I hope you meant 0.0015 for rod and 0.002 for mains, otherwise I'm already too loose on mains, with 0.002 with ACL Race std bearings?
 

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Never finishes (TWSS)
91 Civic SI hb/ 01 GSR
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i ended up with .0019-.0018 for mains and .0016 on the rods. lol i didnt have a choise in the matter but that what they ended up being. my motors N/A. on a built motor i would look for 2 thou on the mains and 1.5-1.7 thou on the rods
 

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Discussion Starter · #7 ·
So I should be ok with what I get now: 0.0015 on the rods and 0.002 on mains with the std ACL's for a normal engine rebuild. I also have no choice unless I change bearings or polish crank, so I would like to keep it as is, unless someone tells me it will be too tight for boosted engine?
 

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1988 Honda CRX
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It's a good idea to polish the crank anyway even if you only take so little off you can't measure it, just to get a perfect surface finish.

My experience with ACL race is they all give an extra 0.001" clearance over ACL std or non race. The Race certainly have a dark grey lead colour soft surface. I can't speak fro ACL std, but I expect they are a harder more aluminium surface that wears longer but is less forgiving and more likely to damage the crank if it does nip up.

I would light polish and run it.

With Eagles it is wise to check bearing crush. I prefer the tight endof the spec.If you change it you need to recheck bearing clearance.
 

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fa5 si e92 335is
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It's a good idea to polish the crank anyway even if you only take so little off you can't measure it, just to get a perfect surface finish.

My experience with ACL race is they all give an extra 0.001" clearance over ACL std or non race. The Race certainly have a dark grey lead colour soft surface. I can't speak fro ACL std, but I expect they are a harder more aluminium surface that wears longer but is less forgiving and more likely to damage the crank if it does nip up.

I would light polish and run it.

With Eagles it is wise to check bearing crush. I prefer the tight endof the spec.If you change it you need to recheck bearing clearance.
Isn't it wise to check bearing crush with any brand rods?
 

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Micro Polish counter clockwise to start new. I'm sceptical of the clearance issues being too tight or too loose. Formula 1 is my reasoning. They have to heat the water and oil to 80°c for x amount of time before the engine can be started due to the tolerances being so tight the engine won't budge at 20°c. Same with the gear box. So I'm wondering if we should be heating the block and internals to 176°f and checking tolerances. Just thinking.

So you should be good on the clearances as long as you choose the appropriate oil.

You asked.
 

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Isn't it wise to check bearing crush with any brand rods?
I wouldn't bother on Carrillos, or Oliver, or Pauter or Argo or GRP or BME if they where all brand new. There was also a time when I would not bother to check Crower, however I think they are now coasting on the reputation earned when Bruce Crower ran the business.
 

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Micro Polish counter clockwise to start new. I'm sceptical of the clearance issues being too tight or too loose. Formula 1 is my reasoning. They have to heat the water and oil to 80°c for x amount of time before the engine can be started due to the tolerances being so tight the engine won't budge at 20°c. Same with the gear box. So I'm wondering if we should be heating the block and internals to 176°f and checking tolerances. Just thinking.

So you should be good on the clearances as long as you choose the appropriate oil.

You asked.
If the piston to bore is that tight, how do they assemble the engine.

F1 I presume have a high strength alloy block, high strength forged pistons and run the pistons in a Nikasil treated aluminium bore. The co-efficients of expansion of all metals used for bore and pistons will be fairly similar, but with the piston still likely to be highest, so as you heat the entire engine, the piston to bore will get tighter, not looser.

Certainly when you run the engine the pistons being in direct contact with the flame and only indirect contact with the water jacket while the bore sees little flame in the bottom half and is in direct contact with water, the piston runs a lot hotter than the bore so for that reason alone, the clearances will close down, not open up as you start and run the engine.

Same deal for big ends. All metals are high grade steel and expand at the same rate, but the rod gets more cooling than the journal of the crank.
 

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I wouldn't bother on Carrillos, or Oliver, or Pauter or Argo or GRP or BME if they where all brand new. There was also a time when I would not bother to check Crower, however I think they are now coasting on the reputation earned when Bruce Crower ran the business.
what about manleys?
 

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I have only ever had one set of Manley rods. They where aluminium and it was a long time ago and they measured up perfect. I can't say if they have maintained their quality but I suspect not. I would measure a few sets before I regained confidence.
 
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