tr3a -tr4 engine /head

[a turner carbs]

Hi,

Following on from my earlier question;

I have striped my engine further and found 120thou shims under the rocker pedestals, the head to block thickness is 3" 258thou and approx 3" 183 for the head its self.

The valves are have 312/ 1000, the head also has an alloy plug stamped USS and I have found N59 cast near number 4 cylinder.

 

I would appreciate peoples thoughts on the head thickness and pedestal shims.

 

Regards Andrew

Edited July 9, 2010 by a turner carbs

[Rhodri]

http://www.tjwakeman...R/FAQ_heads.htm

 

Andrew, this website is worth looking at and includes head depth.

 

Rod

[a turner carbs]

Thanks Rod it looks like it has had a 147thou head skim!

[TR 2100]

Thanks Rod it looks like it has had a 147thou head skim!

 

That is a LOT!! At least it removes entirely the shroud around and

over the inlet valve.

 

The shims used to be fairly standard practice in years gone by to

compensate for the skimming and restore the rocker geometry,

rather than using shortened push rods.

It doesn't quite achieve that, but it does keep it a lot closer

to standard.

 

With that much skimming, you will end up with a very high CR

unless you form a squish area, similar to that on standard 4A

heads.

 

AlanR

[ianc]

To get a sensible CR, you can use more than one solid copper gasket (I have used two in order to obtain a CR of a little over 10). The gaskets need to be trimmed to fit the shape of the combustion space in the head and the block, as any overhanging gasket will create a hot-spot and cause pre-ignition (pinking) and/or run-on.

Ian Cornish

[Rhodri]

Adding to the other's comments about high CR, I would measure the chamber volume with a burette and liquid, in case it has already been enlarged to counter the skimming. From this you can work out what head gasket you need to get a workable CR, to suit today's available fuels. Ferriday Engineering, and no doubt many others, will make you a solid copper gasket of any thickness you may require.

 

Rod

[a turner carbs]

Hi, Thanks for the help, I did a compression test this morning and got number 1 185 psi, 2 60 psi, 3 175 psi and 4 170 psi.

This on an engine which hasn't started since 1990.

I took a chance and poured some fuel in and the engine started.

I reassembled the carbs, restarted and ran for about 3 minutes.

When I turned it off the engine ran on for about 10 seconds, this could be due to the high compression or because there was no water.

I'll re check the compression figures when it has cooled down.

 

Regards Andrew

 

P.S The engine had 60 psi of oil pressure while cranking.

[stuart]

Dont run it with no water in it otherwise you are definitely into a major rebuild.

Stuart.

[Dick]

If you divide the compression test figure by 14.7 it will give you a good idea of what the compression ratio is.

 

185/14.7= 12.6

 

Dick.

[TR3BGeorge]

Dont run it with no water in it otherwise you are definitely into a major rebuild.

Stuart.

 

Heed Stuart's sage advice!!!! I did this accidentally, and FRIED two exhaust valve guides and destroyed the push rods. Luckily, I shut it down before the rocker arms were destroyed. THAT is how I learned the difference between a TR3 radiator neck and a TR4 radiator neck. A $700 lesson.

[ianc]

You cannot just divide by 14.7 to give CR because, in compressing the gases, they heat up.

Looking at the fugures for my engine, I would equate 185 psi to something around 10.0 (perhaps a little over), but it does depend on how fast the engine cranks, valve overlap, the type of tester used (mine is a Schrader valve type, similar to the "old fashioned" tyre pressure gauge - no two gauges will give the same reading!).

 

Ian Cornish