Boring out TB42 to 4.5L

[Brett S]

Going to rebuild 4.2 in not too distant future and if reboring may as well go out to stock 4.5L piston size so:
Are the blocks thick enough to go out to 99.5mm?
Do the heads have same valve design and therefore same valve pockets in piston?
What is the stock compression ratio of tb42 and tb45, as might have to turn down pistons a bit so not as to have excessive compression ratio.
Any one done it?
Oh and yes I have searched.

[Hoonz]

would be cheaper and reliable to buy a 4.5 petrol engine and install

[CWBYUP]

would be cheaper and reliable to buy a 4.5 petrol engine and install

My thoughts exactly.

Nick

[90Mav]

no idea about wall thickness. im thinking standerd oversize pistons would be a better option, you would have to look at them side by side i suppose..
bear in mind that increasing bore will increase compression. you could also get some displacement increase by offset grinding the crank, and using undersize bearings, or even diffrent rods. fair bit of homework to do this sort of stuff..

[Brett S]

Buying a 4.5 injected would not be a cheaper option:
have to buy another complete motor that has already done many k's, convert fuel system to efi and change licensing engine numbers with a possible trip over the pits.
I have the 4.2 already and should be able to rebuild it for $1600ish so it would be as new not 150000k's on it.
And i am happy to turn down the crown of 4.5L piston to get usable compression ratio.
Stroking not overly keen on due to having to play with rod lengths and possible block/rod clearancing issues.

[MyGQ]

the TB45 uses the same TB42 block, from memory they didn't change anything apart from the bore and stroke. TB42's can be bored out for the 4.5L specs, have a look at a Gregories manual for the petrol GU and see what it says in regards to bore and stroke, its not that much different from the TB42.

[PGS 4WD]

TB42 and TB45 have the same stroke, the 0.3 L comes from bore only, I doubt the performance difference has anything much to do with the extra capacity but more the higer lift camshaft and better cylinder head and manifold design. I have fitted camshafts and done a little head work with aftermaket tuneable EFI and the output power is as good as the TB45, and all the way down to idle.

Joel

[fwnsp]

hi mate,
i reckon you'd be better off rebilding a tb42 as a tb42 or buy a wrecked tb45 and rebuild that one.

i'm pretty sure they are the same block, but a lot of stuffing around just for the sake of 0.3L

[bigorangetruck]

G`day mate,new to this site,but here something for you,rebuild your tb42 bottom end,fit a tb45 top end.they bolt straight on,and with a aftermarket computer,they go verywell and improve drivability heaps.I`ve just done this to my comp ute(plus a turbo & intercooler),but bought the bits on ebay and cost less than a $1000.All the exhaust bolt up like factory

[Brett S]

So if the head bolts onto a 4.2 bottom end with 4.2 pistons that must mean that both heads have the same combustion volume and therefore it must be the pistons that compensate to make the compression ratio the same.
Would a carby inlet manifold bolt up to a 4.5 head? as i heard the 4.5 has bigger and better ports.

[bigorangetruck]

Yeh mate,the compression ratio isnt affected with a tb45 head,but you cant run the carby and manifold from a 42 cause it`s a completely different pattern,but the exhaust patern is the same.there is other difference like the water plumbing,the factory hoses dont just go on from either model,but a metre of water hose,and we made our own.

[MyGQ]

If you do what your doing look at Straight Gas for the buggar

then u can use the TB45 head and inlet chamber to control the gas flow, get a 4.5L engine out of it and run it cheaper.