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SP250 having the cylinder heads skimmed

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Zbigmak
Posts: 13
Joined: Sun Nov 19, 2017 10:45 pm
Location: Warsaw Poland

SP250 having the cylinder heads skimmed

Post by Zbigmak » Sat Oct 13, 2018 10:00 pm

Can any one tell me when having the cylinder heads skimmed can one still use the original thickness head gaskets or is a thicker gasket required?

John Chatfield
Posts: 27
Joined: Mon Feb 22, 2016 11:00 pm
Location: Shrewsbury England

Re: SP250 having the cylinder heads skimmed

Post by John Chatfield » Sun Oct 14, 2018 9:13 pm

Hi G. This depends on how much you have skimmed off your heads, I am skimming 0.004" off mine and have had the block re-engineered to be bang on front to back and both banks the same height, so taking a few tho. off the block too, takes a very good engineer and a very reliable flat bed. I will be fitting a standard head gasket of thin shim steel, Barry Thorne is making enquiries in to having thicker head gaskets made, John Nash of dec also has o/s head gaskets for sale on e-bay. F W Thornton has head shims available which are stainless steel head savers (fit to the head with blue Hylomar jointing compound THINLY and very EVENLY spread over the head) and fit the standard gasket, all the above depends on if you want slightly higher comp.ratio. and if you are after exhaust emisions limitations, performance etc,etc. I'm no guru but I am learning so much more lately by being taught by an old school engineer who has built an engine to go to Singapore which had performance/emotions limitations to adhere too, it passed those with better than modern Mercedes results so I have a good teacher to listen too. :) :geek:

Zbigmak
Posts: 13
Joined: Sun Nov 19, 2017 10:45 pm
Location: Warsaw Poland

Re: SP250 having the cylinder heads skimmed

Post by Zbigmak » Wed Oct 17, 2018 7:11 pm

thank you for the words of wisdom!
After much debate we have decided to refit the original design of standard head gaskets especially as we have similar to yourself skimmed a smidge (for those of you who are not engineers this is a British Standards engineering term 8-) )
Head gaskets were supplied by Barry Thorne

fredeuce
Posts: 20
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: SP250 having the cylinder heads skimmed

Post by fredeuce » Sat Oct 20, 2018 7:24 am

A small skim of the head and block I couldn't imagine is going to be an issue.
I had my standard cam measured with my cam manufacturer recently and it shows at TDC lift of 0.0239" Ex and 0.0158" In.

So , you will want to know what valve clearance at TDC you have with the head installed. I checked that clearance on my engine with the old gasket in place and took readings of 0.193" In. and 0.200" Ex . That is plenty of clearance. You might want to take those readings to be comfortable.

The only other concern would be if the increase in compression is going to demand a higher octane fuel. With the small skim you are taking off I doubt that you will have any issues here.

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