Cracked N1 Block, Decision Time

[Stoney85]

Ok,

i recently purchased a fairly built R34 GTT, with an N1 24U RB26 in it, GT3582R, 60mm tial gate, triple plate clutch, and a heap of engine work done to it, ran sweet for a while, then started running on 5 cylinders, upon inspection and after some research, the headwork performed wasn't the ideal way to go about it.

I'm still learning about the RB26's and its quirks etc, but from what i can gather, this wasnt built perfectly and i feel it was the lead cause for cylinder 6 exhaust valve to snap at the end of the stem and get munched by the JE piston, possibly resulting in the cracked block

Engine specs

N1 block, bored to 87mm with JE forged pistons, eagle H beam rods, balanced/grub screwed crank, torque plate bored/honed, ARp studs throughout, ACL race bearings, Nitto oil pump, oil restrictor

Head- heavily ported/polished, match ported intake, supertech brass valve guides, supertech 1mm o/size valves, supertech valve springs, supertech titanium retainers, tomei poncam 270* 10.25mm lift, greddy adj cam gears

thats the main specs of the engine, and apparently from what i can gather is that the tomei cams have a smaller base circle than stock (to get the desired high lift without machining the head like the next size up tomei cams) and the way this was rectified to get the desired cam to bucket clearances was with thicker shims, instead of thicker buckets, and to top it off, the shims required their diameter to be slightly reduced to fit into the supertech spring retainers.

I had one issue with this engine whilst it was running, and that was when it dropped to 5 cylinders, upon inspection, one of the shims had dislodged causing the valve to stay just open (different cyl to the one that failed and exhaust not inlet valve)

So when my engine seized, i was cruising back from work, changing from 3rd to second about to turn a corner, doing no more than 3,000rpm in neutral when it went 'rattle, seize', coasted to the side of the road thinking WTF, wouldnt crank, ok shes dead..

Stripped it down weeks later, to find the above mentioned damage, what i dont undertsand i how it managed to do it esp under no load, was it the cracked block first causing the issue or was it the load from the valve head seizing the motor that put undue stress on the block causing it to crack

Not ten minutes earlier before it happened, it was under full load and no dramas with the engine were evident.

It did have sticky valves sometimes, and a head rebuild was on the cards to sort it all out properly so there were never any dramas.

But what are peoples ideas on why it happened and what would you do in this situation?

Rebuild and use the parts i have already with a new block and a new JE piston to suit, along with a head rebuild, and fix the combustion chamber and reseat the valves along with new valves, but what about the valve spring/seat/cam/shim/bucket setup? change it all, or change what to suit?

The other idea was to get someone elses built RB26, that is for sale, drop that straight in after swapping inlets, exhaust, turbo, large capacity sump, coolers, oil drains etc, Vipec wiring etc to suit, and then strip mine and sell it in bits, tomei poncams, eagle rods, nitto oil pump and whatnot

Thanks for reading, any input regardless of opinion is always welcome, and to say that the previous owner knew about these issues and didnt tell me, isnt true, i knew the bloke who owned it, and there is over $50k in receipts over the last 4 years, everything is done properly and if something went wrong he would fix and upgrade it at the same time, i know the tuner who also did the headwork (Grant), who happens to own a tommy kaira R34 GTR with a built engine and an R35 GTR, it was mentioned but was never an issue that needed rectifying urgently

[DVS JEZ]

Sorry to hear.

Its possible the valve was just a mechanical failure, or something has come between the valve and the seat causing i to snap but they are strong little buggers.

Check the valve seat for signs.

What makes u think the block is cracked?

Check the TDC of the pistons in the bore's too especially the one with the broken valve to be sure a rod hasnt bent.

Changing shims to adjust the clearance is normal

[Stoney85]

I'm thinking that if the valves were sticky its possible that it might've been held open long enough to make contact with the piston and just bend the stem, other than that I'm still racking my brain as to how it happened.

The valve seat is a little mashed up do it'll be hard to make a conclusion from that area. I'll try and get some photos up.

The crack in the block is huge, easy to see and there is a coolant weep through it.

I'll check the rods too.

Rb30 bottom end???

[Carbon 34]

The engine failures happen often at no load

My old A12 broke a cam cruising at 60 no load

4g63 gutted itself just off idle pulling out of maccas , broke the internal balancer and it ate the block from less then 2000rpm

I would doubt your block crack happened out of the blue , maybe a casting fault ? Or brittle casting I would get the blue dye and maybe spend a bit on investigating why it cracked " the famous block" it may sound strange but there is a reason people use seasoned blocks they tend to be a better build platform then a new block

Anyway another option a place in adelaide ( bullet cyl heads) says they can cast rb30 blocks with sleeves in alloy per your specs ( like the R35 engines )

I spoke to the guy but the cost was out of my budget 17k bare block but it looked sexy shiny and smoothe

But for the power a 2j or ls6 is a cheaper fix

the rb 25-26 design

Is a good engine but I know when mine blows up its rb34 time , rb30 block with spool stroker kit

The rb lacks torque stock anyway

Best of luck sounds like expensive mess

[Stoney85]

Not sure why it cracked, maybe the excess load when the motor seized is all I can think of, if it was cracked beforehand I would've noticed signs, ie coolant loss or misfire.

I'd love to throw copious amounts of money at it to fix the problem, but I want to do it wisely and will do some research Ito what options I have to choose from

[Stoney85]

$7g for a built rb34 bottom end, bolt up my nitto pump and girdle, larger sump and build the head again.

My turbo would be too small after a 30% capacity increase, it was responsive at just over 3,000rpm before.

That's a lot of money though for a toy

[Carbon 34]

$7g for a built rb34 bottom end, bolt up my nitto pump and girdle, larger sump and build the head again.

My turbo would be too small after a 30% capacity increase, it was responsive at just over 3,000rpm before.

That's a lot of money though for a toy

Yeah 17k is insane unless its a race car or you want a dyno toy his block is designed for dry sump

Rb34 in r34 just sounds nice haha

Its not about how much power it makes the torque increase makes the car much more drivable and seat of the pants fun , except traction problems lol

weld up the N1 block if its not destroyed inside ? but i would dye check it and even xray it to be sure , double check all the bores and crank

Did a harmonic balance issue arise maybe ??? or crank weight hit the block in a out of balance condition ?

Just odd to crack without a lot more damage or freezing temps running tap water for coolant , welch plugs dont aways work as planned ?

[Stoney85]

unless i sleeve the block again, i cant see how else i could reuse it, the crack is visible the whole way down the rear of cylinder 6, can physically feel the raised edge

[StevenCJR31]

i wouldnt try to reuse the block again, it is weakened with that crack and the block will fail

[Stoney85]

To be honest, reusing the block had never even crossed my mind as an option.

Found a stock R33 RB26, I might go with that option, and then maybe build up an RB30 bottom end and rebuild my worked head, and throw that in at a later stage

[StevenCJR31]

^^ thatd be the way i would go, quickest way to get your car back on the road too

[Stoney85]

Looks like I'm going to get a stock rb26, drop that in, bolt up all my gear i currently have and retune to Vipec to suit.

Then decide further down the track what I want to do with the fully worked head, maybe rebuild it and bolt it on the stock bottom end or build it up with another bottom end etc

[DVS JEZ]

Good idea, stock 26 can handle a fair amount of power for a while

[Stoney85]

Stock R33 RB26 will rock up next week.

Now what do people think I should do with it, I was considering to remove the big ends and have a look and maybe replace them all along with mains too, when I fit the rwd large capacity sump, change front and rear crank seals too.

What about fitting the nitto pump I have, will that be an issue if I don't fit the block restrictor which I won't, but what about if I go ahead with fitting the external head oil drain kit too, will that suffice?

Any other ideas, without pulling the motor down to bits?