For the love of a tractor engine: The life and times of the 18R-G

[jabbatron]

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[bholmberg]

interesting.
I'm not an engineer, but my engineer told me grade 12 would be too brittle, and the tty stretch characteristics of a grade 8 bolt would be far more appropriate for an aluminium head. Also, very few bolts from a bolt shop have thread all the way - most look just like the stock 18rg bolts.
I have also heard you can't just tap grade 12 round bar to make a grade 12 bolt, and grade 12 has to be allen keyed because the hex shape crates friction on the surface as the bolt is tightened. must say however I only know this as an architect(ie. houses), not as an engineer. An engineers comments would be far more appropriate.

[3jcelica]

There is a little more to bolts than meet the eye other than just fitting in the right hole.

Firstly a head bolts/studs thread will be rolled not cut resulting in a much stronger thread section.

The bolts/studs material make up will determine its ability to maintain clamping force through all operating conditions.

If you where to buy a bolt from the bolt store I would suggest that the head gasket and bolts are not going to last too long. Factor in the price of bolts from a bolts store in the sizes we are talking and you would be over $8 per bolt or $80 for a head. VPW sell ARP 207 4202 studs I used in my 3tgte for $126 (machining of the posts was required).

I think Yellow Rolla says it best, studs are a engineers choice, bolts are a economist choice. Here is why

When you use bolts to secure the head, the fastener is actually being "twisted" while it's being torqued down. Accordingly, the bolt is reacting to two different forces simultaneously (twisting and vertical).

Studs are installed figure tight => no twisting, when applying torque to the nut, the stud will stretch only on the vertical axis. This provides a more even clamping force, and one that is more likely to be maintained through operation.

Roger

[jabbatron]

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[jabbatron]

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[SilverRA23]

Speak with Atomic Speedware / Arias Pistons in the USA.

They are not $1100 plus.

US$775 delivered for custom 92mm pistons (or what ever size you choose). Takes about 4-6 weeks.

The 92mm piston will then require a Cometic headgasket, also from the USA. I got a deal through work so I won't state what I paid, but its another $200+ I imagine.

[jabbatron]

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[river]

Hi,

You can shoot a PM to YelloRolla (Jason), as he has built a few 18R-Gs and may be able to tell you if there's anything available.

However, I assume you're trying to keep the lower compression ratio 'cos you are looking to turbo the engine? If so, it may be wiser to invest in something a little more robust to "future proof" the engine for upcoming power upgrades.

seeyuzz
river

[jabbatron]

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[jabbatron]

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[jabbatron]

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[SilverRA23]

Ah the life and times of rebuilding an 18rg..

Can anyone tell me if the harmonic balancer is the same 18rc and 18rg?

Apparently my one is flogged out.

Can they be bought new?

[Steve M]

Head Gasket:
92mm bore Cometic Head gaskets are available through Gometic Gaskets Australia in Capalaba, QLD.
(07) 3823 5410.
My brother recently bought one. I think it was about $150.

SilverRA23:
18R and 18R-G have the same harmonic balancer. There are different versions of them, but they all mount and align the same, just different timing marks and more or less pulleys (1-3)

Jabbatron:
Those 1UZ pistons are actually quite different.
With a 1mm oversize set up you'd still only have a compression ratio of 5.4:1, which is not even worth thinking about.

If you're stuck, then look at 20R pistons or early 22R domed pistons (have them fly cut) (39compression height).

Alternatively, 3tc forged pistons are available in an 89mm bore with huge compression ratios. some work could be dome around those. Arias supply 20R, 22R and 3T-C pistons.

[jabbatron]

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[Steve M]

I wouldn't machine the tops off of them as that would weaken their crowns significantly.
flat tops would give 7.3:1 by my calculations.

The standard dome 24.7cc dome will give 10:1 static compression. (This would be reduced when your valve reliefs are flycut into the dome).

I haven't been keeping up with your project but am guessing you're turbocharging it, yes?
If you want big boost, then, yes, compression below 8:1 is ok.

I plan to turbocharge also but have chosen to go for higher compression so that less boost is needed. This should give a more linear power curve and I can run it N/A while I am getting all the turbo stuff together.