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Rb30 bottom end

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Hey guys just dropped my bottom end to a machine shop to have it all machined for assembly(finally decided to give another shop ago after loosing my last block and a fair bit of money to poor quality machine work).

I have 4 questions the 1st one is if anyone here has had first hand experience with grout/concrete filling blocks around 3/4 up the water jackets in a street engine or even better a rb30. The machinest said the i will not notice a difference in water temp but i feel like it is a little unnecessary for mid 30psi of boost i have not really heard of people using block fillers at that level in rb30s.

The 2nd queston is i dont know if i should plug the oil filter bypass valve or just replace it with a new valve people seem very 50/50 weather to do it or not. The machinest said he normally pulls the valve out and plugs the hole up. But my last engine had the valve in it still and it never gave any problems that i am aware of.

3rd how are people going about having a bottom end machined and checking it all to make sure its right with out the shit part of paying the money only to get the block back and its wrong or in my last case destroyed and having to deal with the "mate it will be fine just screw it together it doesnt matter that its 0.002" over top size we do this every day"(main tunnels all over the place full of taper and different sizes)

This machinest i am using now is a 3 hour drive away so will make it a little harder if this happens again

Also when a cylinder becomes distorted from cyl pressure what sort of shape does the cyl generally end up?ie. Egg shaped? Reason i ask is this is the reason the machinest suggests filling the block is to stop cyl distortion. Now when i pulled the last motor down the bores all had taper from top to bottom but were not so much "out of shape" the worst bore had 0.0015" of taper from top to bottom. But thinking it might have just been from a poor hone job in the first place as there was fair bit of dodgy machine work in the motor when i pulled it down

Cheers guys

I feel your pain with shit machine work. Had a horror run myself from multiple shops on my subaru.

1st shop took the best part of a year to close deck the block. Then i get it back and its beat to hell with dents all over the parting face and even into the main tunnel.

Then i go to another shop to get a line hone performed to suit ARP main bolts and fix the damage from the first shop. And the stupid fucks forget to tighten all the bolts when honing it.

The industry is a fucking disgrace.

I did read about your incident the other day sorry to hear mate it is unfortunate but seems to be a very common thing

Sorry for the late reply but I'll add my my replies here.

1. I've grout filled a number of blocks and for a street application I generally wouldn't bother. I've done a few street 4G63 engines that I've 1/2 filled and it hasn't been detrimental to the ability to control temp, however you also need to consider that the major cylinder pressure is occurring through the first 20-30 degrees of crank rotation so solid filling the lower half of the block isn't going to help too much with bore distortion. Ultimately it doesn't sound like you're trying to break any world records for power with the RB30 so I don't think it's justified.

2. The oil bypass is a bit of a personal preference. The majority of oil filters include a built in bypass inside the filter which is utilised if the oil filter media becomes blocked so for me it's a bit of a moot point.

3. The machining is a tough one. Really you need to start by finding a machinist that has an excellent reputation. This is tougher than it sounds but your local car club is probably a good place to start - Find out who is running high power engines and who they've used. I wouldn't accept anything that's 2 thou out of your spec from any machinist.

4. When a cylinder distorts from excessive pressure it will become out of round, or egg shaped as you've referred to. It's likely that if you're measuring taper in the bores that this is more in line with the boring and honing process.

Hi andre sorry for the late reply i am sort of just getting back in to this engine thank you for your replys so far.

Would i be wrong in thinking that the main tunnels/any tunnel should be with in the bottom and top size tolerance that the bearing manufacturer gives after line boring/honing?

obviously if we are shooting for a looser clearance we would end up at top size and for a tighter clearance closer to bottom size.

It has been playing in my mind abit and i am a little paranoid about turning a bearing.

If we were to end up outside the tunnel size tolerance what would you call except able if it was over top size.


Hi Jesse, you've pretty much nailed it with regards to the tunnel sizing. The problem with being outside the tolerance stated by the manufacturer is that it reduces the crush on the main bearings which in turn can result in the bearing spinning in the housing. So to be clear, I would not recommend running the tunnel beyond manufacturer tolerances.

Ok cool just wanted to make sure i was on the right track and not getting myself worried over nothing. Thank you for the fast response andre

On another note is there any plans on doing a rb build at all?

Also whats your take on squish? I spoke to the machinest and by the time the block was line bored/honed it put us at 0 deck hight and we had to skim the block to get a good surface. he said it would put us at about -0.004", i have a 1.2mm tomei mls gasket here for it and the pistons are a 9.0.1 flat top with a very vary slight dome and two valve pockets. i cc'ed the chambers in the head and they sit at 53cc and with the deck hight and gasket it gives a CR of 9.1.1 will be using e85 fuel also

Not sure if you are familiar with rb30 single cam heads/chambers. Just wondering what your thoughts are on boost and squish are? There aeems to be many different views on this but was wondering what you have found with your experience/if you played with it much?

We will be doing an RB26 build later this year I believe. I've never dealt with the single cam RB30 head so I'm not familiar with them. With the RB26 it's common practice to remove the squish pads from the head as these can actually make the engine more knock prone.

Ok then might be something i have to look in to some more.

Can you tell me if head gasket manufacturers listing for gasket thickness is compressed thickness or the thickness when relaxed? I did mic the gasket i have and it seems that the listing would be for compressed thickness. Just wanted a second opinion as it seems i will be creeping up to 0.040" piston to head clearance

The head gasket thickness listed will be compressed.

Thanks andre just didnt want to over look something so silly just incase

Ok so i picked up my block from the machinest all seems to be fairly well done compared to the last block i lost.

The only thing is when i measured piston to wall clearance i get anywhere from 0.0048-0.0053 min clearances across all 6 bores. The pistons i am using are a full length 2618 86.5mm je piston and they recommend a 0.0045 piston to wall clearance.

do you see that sort of clearance being a problem? I am hopong that the piston to wall clearance doesnt make it noisy all the time. I could live with abit of noise when its cold just dont want it to be really bad.

It did have a set of 4032 short skirt pistons in it last time with 0.0045-0.0055 piston to wall that was rather noisy at times.

I am hoping with the change in material and the longer skirt i will be better off

The new piston is roughly .333" longer then the old piston from the crown to the bottom of the skirt.

Any info would be appreciated


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Most machinists tend to take their own initiative and err on the large side with PTW clearance as far as I've found, so those measurements aren't unexpected. in reality with a 2618 alloy they will be just fine. You may find that after the engine has some miles on it that it may be a touch noisy on a cold start but should be absolutely fine at operating temp.

2618 has a higher coefficient of thermal expansion compared to 4032 so it requires totally different PTW clearance an 0.0045 is quite loose for 4032.

Ok cool i was thinking that being 2618 over 4032 and being a longer skirt would work in my favour. My thoughts exactly when i pulled the old motor down.