3.2 SS Head work

[Mark McClure]

Hi,

Just wanted to get some real life feedback from people who have already done this conversion. On the conversion is it common to have the heads machines to 98 mm. I have another thread open relating to my deck height issue, hopefully this topic will provide some of the answers I am after.

If the head on the conversion are machined how and what profile?

Why?

Thanks

Mark............

[ChrisBennet]

You add a chamfer to the edge of the combustion chamber to transition from 95 to 98mm.
-Chris

[Mark McClure]

Thank chris, Since my heads have the chamfer it appears thath the SS kit was removed before the engine was given to me. That explains a lot of things!

It has now created a big issue for me! I am having siiues with the deck height due to the chamfer. I do not thing that it would be a good idea to use the heads on 95 barrels.

Any thought would be good!

Thanks

Mark.....

[Mark McClure]

Come on guys a bit of advice here I am struggling with the best move......

1. Go ahead as is........not worrying about the larger head mating size.

2. How to adjust the dack height that it too big already with only 1 .25 gastet

Thanks

[davidppp]

Hello Mark.

If you have more than say 0.7mm clearance between the piston top and the cylinder top, you can machine heads to remove the chamfer..its normally very slight so as to maintain squish.

I'm assuming you want to use the 95mm barrel/pistons in an engine which was modified to use the 98mmones..

Kind regards
David

[Mark McClure]

David,

The chamfer is quite a lot. I did consider machining the heads by 0.5mm but in the end I found a head place that will weld and then machine the heads back to the 95mm. After that I will CC the heads and measure the deck height and piston 2 head clearances. If need be I can then savely machine the heads to add compression.

Thanks

Mark......

PS.......I have not found any information on the board that even mentions head work when doing a SS conversion.

[davidppp]

Hello Mark.

I'm not fond of welded heads on any engine...and most defintely not the 911..the head dimensions are very crucial with cam carrier etc etc..I'd far prefer to remove the 0.5mm and sort the compression myself..

Or get some 98mm barrels...

Kind regards
David

[Mark McClure]

David,

The budget does not stretch to the 98 barrels, plan B is to mill 0.5, plan C is weld/machine! If I had know about this in the first place I would not have bought the bloody engine.

Anyway Plan B, the piston to head is 1.5 just now so removing 0.5 would leave the piston to head clearance in the perfect position. However it would not have removed all of the chamfer. My concern was that this pocket around the piston would still be 1.5mm and would create more of a detonation issue, possibly more so that leaving it at 2mm.

The head people have reasurred me that it will not distort the head and that the milling will be done parallel to the cam house mating surface.

I have heard of people welding the plug hole and boring to the same size for both plugs in a twin plug configuration. If there are any distortion issue surely nobody would do this.

Thanks for the feedback I though that I was talking to myself for a while there!

Cheers

Mark.....

[Wayne 962]

Can you post a pic of the chamfered edge you're talking about?

-Wayne

[Mark McClure]

OK here is a picture of a view down the barrel as it is placed on the head on the bench. As you can see there is a ring around the base which is the chamfered edge. I will also put a closeup picture of the edge.





As you can see the machining has not been done very well.

Thanks

Mark.........

[spydr32000]

Mark the squish band looks to me like it has been done by hand. The chamfer(squish band) should not protrude beyond the diameter of the cylinder, if that does occur then you promote corrosion at the joint between head and cylinder, which is never a good thing, and should be avoided at all costs. This, in turn will help promote other problems as well, such as pinging, detonation, running on, over heating of the combustion chamber,all of which aggravate each other, not a good situation!
Mike

[Mark McClure]

Spydr,

You are right it is a very amaturish attempt at machine work. The chamfer was done to accommodate the 98mm barrels. The previous owner has taken them off and replaced them with standad 95s. This is what has caused me many problems with trying to get the engine to run properly. The B*****d is now saying he known nothing about it! I am surprised that it has not actualy detonated it's self to death. I thing the saving grace is that the compression has been so effected with the twin plug and the machine work that it could not ping.

I have always had issue trying to get the engine to perform. I bought it with ITB's twin plug and a Microtech ECU. The last compression test showed 100 to 105 on each pot.

Cheers

Mark........

[spydr32000]

Mark some people do not deserve the privilege of working with these engines. I have seen a few examples of the sort of thing you have described, in recent times, I am never surprised at what I find these days.
Mike