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Re: Pair of SP250 or saloon cylinder heads

Posted: Thu Jul 11, 2019 10:00 am
by timmartin
Thank you Mike.
I had already discussed this (to me) fairly encouraging head with Russ.

My first reservation was that it looked as if part of it had been fettled using a coal chisel. Russ, of course was more professional. He pointed out that:
1. A piston had broken up in the left hand pictured cylinder, broken pieces of ring having been knocked into the head, and
2. The head had already been skimmed too much for my use. This is liable to cause over-thinned parts to overheat and pre-ignition (pinking). (This is the problem with my own heads)

Thanks again,

Re: Pair of SP250 or saloon cylinder heads

Posted: Fri Jul 12, 2019 12:39 pm
by timmartin
Colin and Graham. Just in case this changes your opinion about how much your heads have been skimmed already, this is how Russ checks whether there is enough metal left for him to rework a head. (Measuring the overall thickness of a head can sometimes produce either an over-pessimistic or an over optimistic-conclusion!)

1. Straight edge on the machined face, across the middle of each cylinder.
2. Measure depth to centre of combustion chamber, between the valves.
3. The minimum useable depth is one inch. (When new they are up to one inch and 40 thou. (1.040”)

My posting this does not imply that, unlike me, you need to be told how to suck eggs. Just double checking...

Thank you.

Re: Pair of SP250 or saloon cylinder heads

Posted: Fri Jul 12, 2019 12:56 pm
by grahamemmett
Good information as I was to measure the depth of the head being 3.000 inches

Re: Pair of SP250 or saloon cylinder heads

Posted: Fri Jul 12, 2019 3:19 pm
by Warsash 2
Hi
I have been in touch with the SP club and they said that the heads when new the thickness was 3 inches, which indicates that Grahams head have not been skimmed. As such they are hen's teeth.
Regards

Colin

Re: Pair of SP250 or saloon cylinder heads

Posted: Fri Jul 12, 2019 6:12 pm
by timmartin
Thank you Colin.

I too understood that the nominal overall thickness of a new, machined head was three inches.
But I have heard of thicker ones being seen, up to as much as 3.060”.

It does seem unlikely that one or more of these thicker heads will turn up during my search, but it does suggest to me that measuring the combustion chamber depth may be the more certain way of assessing a used head?
Or have I got it wrong somewhere?

Re: Pair of SP250 or saloon cylinder heads

Posted: Wed Jul 24, 2019 8:03 pm
by tjt77
On the question of head thickness :- 3.0" when new... with std pressed steel gaskets skimming up to .035" can be utilized..
The alternative 'composite' gaskets as supplied today are approx .040" thick.. in practice these allow for a safe skim of +/-.060"

Re: Pair of SP250 or saloon cylinder heads

Posted: Mon Aug 05, 2019 11:03 pm
by grahamemmett
Tim, are you still after the two heads? I’ve located two which have the required depth, pretty sure never been skimmed and have little visible corrosion around the waterways.
2A7182B6-A41D-491E-A6B5-CBFD4C8EF8A4.jpeg

Re: Pair of SP250 or saloon cylinder heads

Posted: Sun Aug 11, 2019 9:31 am
by timmartin
Thank you Graham. I have replied to you by email and am consulting Russ and Andrew.

Re: Pair of SP250 or saloon cylinder heads

Posted: Mon Aug 12, 2019 8:59 am
by classiclife
Hello Tim,

I have sent you a PM that may be of interest to you.

All the best.

Richard.

Re: Pair of SP250 or saloon cylinder heads

Posted: Thu Aug 15, 2019 9:37 pm
by Ozzsp250