Astron heads explained.

[A112H]

Astron I (1.85, 2.0 and 2.6)
GE - GK Sigma 1979-85.
The 2.6lt has a small combustion chamber but ran dished pistons to lower the compression; it uses 35mm diameter exhaust valves and 43mm diameter inlet valves. These were all designed for leaded fuel.

Astron II
The Astron II had a few changes, notably hydraulic tappets, replacing the manual tappets in the previous Astron I.
In December 1985 the Astron I 2.0-litre was dropped, as MMAL did not believe it warranted the conversion to unleaded fuel introduced in January 1986.

M1 - M5 - GN Sigma 1985-87 & TN – TP Magna 1985-91.
Larger hemi style head all much the same 40mm diameter ports using a 38mm diameter exhaust valve and a 46mm diameter inlet valve.

Pajero and Sigma GN.
Ports are much the same as early Magna as above.

M6 - M7 - TR Magna 1991-94.
Uses the same large open hemispherical chamber as above but bigger ports at 42mm diameter with a better flow to the inlet port. They use the same 38mm diameter exhaust and 46mm diameter inlet valves.
This head is the best flowing in stock form.

M8 - M9 – TS Magna 1994-96.
This is the last of the range the open chamber heads; they were dropped for a kidney shaped chamber of smaller size matched to a kidney shaped dish in the piston. They use the same big ports as the M6 and M7 and same nice inside radius (flow) to the inlet port, the same sized valve as all the other Astron II heads. Flow is reduced slightly only because of some masking of the port due to the combustion chamber.

M28 is a new casting on the old Astron II rwd design

Note; the Magna head has a large water gallery at both front of the head and toward the rear whilst the rwd head has the same front gallery but has a small rear gallery.

The 2.4lt 4G64 in TE-TF Magna's is not compatible.
When fitting a Pajero or Triton series II head you will need to use an electric fuel pump as the mechanical pumps are not compatable.

[Superscan811]

FYI:
This is what an Astron II, M8 combustion chamber looks like.



It is approx 65cc

Cheers.

[Cottees]

From measurements I have done, the Astron I's combustion chamber is around 61.6cc.

[Xaser]

I dont have exaclty how model is, is a 4G52 engine with original twin carbs.



If you says me, i up all the meassures


PD: have solid tapets, no roller, no hydraulic

[Cottees]

I dont have exaclty how model is, is a 4G52 engine with original twin carbs.

The 4G52s with twin carbies had a compression ratio of 9.5:1. That is the same as the aussie 4G52s, but from what I have seen, the aussie ones got it from having slightly raised pistons. Looks like the Japanese version had smaller combustion chambers.

[Xaser]

Cottees thanks!

The combustion chamber volume is 55cc. ( 80mmx 82mm Oval size)

Exhaust Valve = 38mm ( 82.5 Grms)
Exhaust Port = 39mm

Inlet Valve = 42.5mm ( 89.5 grms)
Inlet Port =36mm

Inlet Port Lenght = 86.89mm ( Max) 45mm ( Min) 65.94 ( Med )
Exhaust Port Lenght = 102mm ( Max) 54.5 ( Min) 78.25 ( Med)


Inlet Port Area = 74.25 mm2
Exahust Port Area = 95.87mm2


Spring Weight = 72 Grms
Spring Seat Weight = 5grms ( Lower) 21Grms ( Upper)


In the next Week i will Measure the STD Cam with Cam Doctor

[Superscan811]

Re-CC'd the M8 head today (with the kidney shaped chamber) and it is actually 62cc.

I also CC'd the Magna M5 head and it was 72cc.

BTW: would it be possible to add a spreadsheet type of list that includes:
1. Astron 1 or 2
1. Head Number
2. Chamber CC
3. Port size
4. Valve size

A pic of the inlet port side of the head along with the chamber would also help.

This would be an invaluable tool for someone wanting to build up an engine, or just figure out what they have..


Cheers.

[BAD-SIG]

Please delete.

[twocarbs]

Hi Does any one know if there is an advantage in fitting a m7(ts magna) head with roller rockers and camshaft to a mh triton with a m28 head? Is the cam profile the same between cars and commercial? Thanks in advance for your help