Cylinder head

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win
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Cylinder head

Postby win » Tue May 21, 2019 3:39 pm

Hi All
1275 midget engine 12cc-Da-H-15908. Head 12G 940-323. HIF 38 with LCB and (1 & 3/4") 2 silencer exhaust, runs very nice, or did.

I had a slight misfire this morning, checked compression 1=180psi. 2=140psi. 3=140psi. 4=180psi.
Removed head, very slight blow across 2&3, so just caught it in time.
I had a 230 mile fast run home on Sunday, only stopped for fuel, Hmm.
I was surprised how much carbon was in the head, but I did put oil in cylinders after I checked pressure first time to eliminate a cylinder problem, so could this account for this?
Also the pump to head bypass hose was blocked solid with crud.

My question is, would there any advantage in having the head skimmed, and by how much, to raise the compression, the head thickness is 69.5mm at the moment, and is straight with a steel rule.

Are there any higher tensile head bolts available, 3/8" UNC one end and 3/8" UNF other, by (3 & 1/2") and (5"). I torque mine to 44FT LBS, could we raise this.
Is there any thing else I should look at, or should I just grind in the valves, and rebuild, with a bit of grease on the new gasket.

Kind regards Win
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South Yorkshire

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philthehill
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Re: Cylinder head

Postby philthehill » Tue May 21, 2019 4:21 pm

Your head appears to have been lightly skimmed. already

Ex factory the head should be 2.75" or 69.85mm from top to bottom face.

I would suggest that you can take a total of 0.060" off the face of the head without any difficulty.

The limiting factor is the oil transfer cross gallery which runs across the front of the head. There is a brass bung on the front N/S of the head which identifies its location.

You can measure down the oil up gallery and so long as you have at least 0.040 spare between oil cross gallery and head face you will be alright.

See Vizard "Tuning the -A- Series" book for further details regarding the cross gallery.

As regards higher tensile studs use Marina / 'A' Plus type head studs which can be tightened to 50lb ft when using the flanged nuts.

Before fitting ARP studs that is all I used and never had any problems even with high compression.

Grind in the valve and re-fit and enjoy.

Grease the gasket and re-torque after the first heat cycle and at 500 miles after re-fitting the head.


win
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Posts: 195
Joined: Mon May 04, 2009 5:41 pm
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Re: Cylinder head

Postby win » Tue May 21, 2019 4:33 pm

Wow

That was quick.
Many thanks for the advice and info, just what I needed.

Kind regards Win
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South Yorkshire


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