Building 3 Litre Gtr , Piston Are 30 Thou Out Block

[Gtr3.0l]

Block been shaved , and head , put back together and piston 30 thou out block , ideas please and could this be fixed with thicker 1.8 mm Steal head gasket ??? Big money spent on block and head what could I do

[Moodles2]

English for starters.

[Ryanrb25]

I think it's best to speak with a repretable Engine builder about this....I would imagine as long as the ring seal on the head gasket is big enough so the Piston has clearance then i would imagine it should be fine with thicker head gasket.

[Gtr3.0l]

Cheers Ryan , the story is I have a r32 Gtr 3l bottom end 26 head . Detroit locker in the arse crazy fuel setup os gieken gear box, Carbon twin plate .gt28 60 -10 turbos 260 cam 2000 I'd injectors 6 boost manifolds titanium ferrera everything for the heads oversized valves Killa springs , made 420 kw on 17.8 psi done sixth piston ring , stripped it done pistons ,rods , bearings and done better oil return better oil pump nothing else can be upgraded ! Lol but on putting it together my mechanic has found the pistons are 30 thou hanging out the block , he done the Maths and said a 1.8 head gasket would solve the problem . I'm a bit worried about the idea , don't know how it's happened to be out so far. Wondering the pros and cons on fixing the problem like that ?? Didn't think after spending so much cash I would have this problem arise at this stage of the build . Any thoughts would be appreciated

[Aberax]

The pistons in my build hang out by 10-15 thou, I am using a 1.5mm head gasket from memory. You could possibly have valve reliefs cut into the pistons, or have the pistons shaved and balanced again. Best bet to speak to Rhemac or another engine builder/machine shop

[Gtr3.0l]

Cheers I'm onto it a soon as they open tommorrow . Thanks

[Ryanrb25]

Lewis engine builders in Mt barker would have a good idea aswell.

[SLED]

how much was shaved from the head and block...surely anyone reputable would've measureed the amount removed?

You mentioned larger valves which even if a thicker head gasket resolved the .75mm (.030") piston protrusion, you'll still have to factor in the amount of valve lift......did you also increase cam lobe lift......even if you didn't, a larger valve head will travel further out of its chamber because of its angle.

There are way too many factors to consider and everything should've been planned together before removing any metal, anywhere....did the machinist have some sort of plan in mind before going nuts on a surface grinder?

Abe's example won't help you...he has .25mm protrusion and more than likely standard size valves.....not sure if he's running more lift though.

PS: I wouldn't go maching piston tops unless you like flirting with death....especially in motors that are renown for smashing already very weak top lands....worse comes to worse, you may have to get a de-comp plate made.

[Aberax]

Abe's example won't help you...he has .25mm protrusion and more than likely standard size valves.....not sure if he's running more lift though.

Yeah, Standard valves with 8.5 cams

[Race__24]

Would shortening the rods be an option?

[SLED]

how do you shorten conrods without cutting them in half.

you could machine the mating surfaces of rod and cap then line bore to get the correct diameter again...but then you would have to re-cut the brg tangs followed by balancing them again.

Sounds like a pretty expensive option not to mention it would weaken the rods

But I like your thinking though

Only way around this one is to find out how much metal has been removed in total then replace it with something of similar thickness over and above a standard head gasket thickness.

If the machinist has no recollection of how much material was removed, you'll have to measure (accurately) the overall thickness of the head and block....only an engine reconditioner will have outside mic's or calipers that size.

Good luck with it

[Race__24]

Yeah, I was thinking removing the caps, machining the rod side down the 30 thou picking it back up, machine and re bore it.

You kind of forget about the cost of machining when you do it all the time.

[D_Stirls]

New pistons with different pin height will solve the issue

[SLED]

def a solution Dale bit who makes a piston with a lower pin height?

regardless, he also needs to consider how much has been taken off the head's surface now that he's running a larger valve which all adds to valve protrusion...not to mention that by bringing cams closer to the crank you also have valve timing issues that you need to sort out...but shouldn't be too much of an issue with adj gears.

I'd still want to know how much material has been removed for peace of mind

[shy_s6]

so your engine builder didnt measure anything before he machined? maybe head/block been machined too many times?

[GTR1993]

So much crazy talk happening here, de-comp plates what the hell, it is in reality a pretty straight forward build.

If they have machined off too much then a thicker gasket could indeed fix you problem, with out measuring everything I couldn't tell you what you need. Have the CC'd your combustion chambers? If we had that information and the cc of the dome in your pistons we could at least then try to work out the comp ratio. As far as the pistons hitting valves you will need to dummy assemble the motor with some Plasticine and turn the motor over, dissect it and then measure the piston to valve clearances.

Sounds like a recipe for disaster if this has come from your "engine builder"

[Dahtone Racing]

What a mess, mate I really feel sorry for you.

If they have made a mistake like this only god knows what else has been butchered.

Time for a new engine builder I think.