How much can i Showel the head, 18R?

[MarkIIRx12]

Hi

Im taking the head off my 18r and im going to use the opportunity to shave some off the head, does anyone know whats the maximum safe limit for them to grind of the head? is 2mm too much, 3? i dont want to get problems with the valves going to near the pistions.

so i guess im asking whats the maximum mm's to grind it off and still be safe?

thanks in advance for your help

[timbosaurus]

Sorry mate, I've got no idea really. The compression in an 18R is pretty low, and the cams aren't very lumpy, so I think it will take a fair bit of shaving before you will have problems.

Having said that, the 18R isn't commonly regarded as a performance engine over here, so if someone is going to do this much work to their engine they will usually go to the 18RG. That my be why there is a lack of replies

[MarkIIRx12]

Hi again

Thanks for ur answer.

well its definitly not going to be a performance engine, but its nice to have some extra power in a daily driver, and the cost of getting the head cut down a bit is very low, so thats why i was thinking about it.

hmm, is there any easy way to find out how much i can take of the head without getting any problems?

[gianttomato]

Your machine shop will have the maximum amount that can be removed from the head to keep the head serviceable in some reference book somewhere.

That said, you can go past the maximum serviceable limit. What I used to do is put some plasticine on the piston, bolt the head down with the head gasket in place, time in the camshaft and spin the motor over a few times by hand. Rip off the head and measure the thickness of the plasticine where the valve has left an imprint. Ideally, the piston to valve clearance should be no less than about 60 thou* (to allow for stretch etc). Subtract 60 thou from the valve to piston clearance as measured with your plasticine and there's the maximum amount you can shave off the head. Of course this doesn't take into consideration if you want to run a longer duration higher lift cam later on, or what the final CR is (might be a prob if you have shitty fuel in your area).

Hope that helps.

*That figure might be 40 thou - I honestly can't remember.

[MarkIIRx12]

Hi

Thanks for ur answer.

i really doubt the machine shop here have any list for how much they can machine off this head, they hardly know anything about theese engines here anymore, even at toyota themselves they have a hard time getting info for me when it comes to my engine.

anyone knows whats considered the service limit on theese engines?

im not looking to take off extremely much, was thinking in the area 2 mm, but i never took anything off 18R heads before, so im not sure if thats considered extreeme or not.

Measuring it with the use of plasticine is doable, but im usually not that great at things that deals with clearing and micrometers, so im not sure i trust myself enough to measure it that way.

[gianttomato]

I'd imagine 2mm would be well beyond the serviceable limit. I presume you know that will throw the cam timing out too - can't remember if they have a couple of dowels so you can time the cam in wit servicing of the head.

I think you're going to have to suck it and see. If you botch it, are 18R heads that hard to come by in Virginia (I presume USA)?

I doubt there will be a great repository of info regarding the old 18R anymore. Try PMing 'the chuckster' - Charles has a turbo one and may have some info that could help.

[thechuckster]

i don't know what the limit for decking is - you'd have to do an interference test as suggested by gainttomato. Personally, i dont think there will be great benefit - i'd just skim it so the head-gasket seals correctly on it.

i you want power from an 18R, the easy solutions are: 4-2-1 extractors, a DCOE-style webber carbi, improved spark (e.g. breaker-less HEI from a 22RE), more spark advance and running high-octane fuel.

I think decking the head is going to change the combustion chamber shape a bit (it's a wedge shape opening up towards the area of the valves) and these engines are already prone to pinging if you do weird stuff to the combustion chamber.

In my case it was to open up the chamber to lower compression - it pinged badly with boost and too much spark advance.

You need the squish area to make the chamber work as designed, i know that less squish area (what i did) makes it ping badly but i'm not sure if adding even more squish area (by decking it) will improve or worsen things.

chees,
Charles.

[RT104GT]

Hi

Im taking the head off my 18r and im going to use the opportunity to shave some off the head, does anyone know whats the maximum safe limit for them to grind of the head? is 2mm too much, 3? i dont want to get problems with the valves going to near the pistions.

so i guess im asking whats the maximum mm's to grind it off and still be safe?

thanks in advance for your help

Milling a twin ohc head has major problems to solve not the least being shimming the new camshaft if you do that as well.

There are heaps of documents telling about the pitfalls so do it right, or do it again and again.

As for taking up the slack in the timing chain even new, this will eventually be an issue.

[sleepin22]

hey chuckster u reckon PULP is ok in the 18R?

and is additive needed?

[allencr]

The exhaust are the only ones that come close to touching. The intake cycle doesn't come anywhere near them, but with a 300+ cam & larger intakes, they may come close.
On the exhaust stroke, at about 30 degrees BTDC, and every 5 degrees until TDC, push/shim/adjust an exhaust to see if & when it'll hit.
A 45 degree valve angle would make its distance down toward the piston 1/2 of its travel, twice what you could mill/shave, but it'll contact at a different point if the piston is dished/domed/flycut/whatever and won't be that accurate.
Anyway, I think you'll see that there is plenty of room! Weaking the head on old stuff was impossible because it was so crude & beefy & stone axe, but the new stuff is much better designed, with less room to play around with.
Also, if it's OHC, the cam timing has to be right, and extra chain/belt slack taken care of.

[thechuckster]

sleepin22: i use any petrol in the beast - no point wasting money PULP unless you're going for a highway or 'spirited' drive.

ULP is more prone to pinging, but now that i'm running spark-n-fuel EFI i can tune around some of those issues.

no additive needed (mine is an 81 model) - waste of money unless you have an early 70's motor or older (or an Oz built engine).

[sleepin22]

mine's a 73 JDM. So i guess the answer is yes for the additive.

[thechuckster]

depends how often you drive the car - if it's not a daily driver i wouldn't bother as that stuff isn't cheap and is quite piosonous.

[sleepin22]

well it will be for weekend use

[thechuckster]

meh ... use PULP and when the engine wears out, put a 18RGUE in it ;-)