Dave McCulloch Posted October 16, 2004 Share Posted October 16, 2004 Anyone know / recommend somewhere in W. Sussex to get a skim on a K series cylinder head? Need to get 10 thou removed now I've finished porting it. Thanks Dave Link to comment Share on other sites More sharing options...
mahatma Posted October 16, 2004 Share Posted October 16, 2004 Scholar are in West Sussex aren't they ? Andy Link to comment Share on other sites More sharing options...
Dave McCulloch Posted October 16, 2004 Author Share Posted October 16, 2004 Thought they were in Suffolk? Link to comment Share on other sites More sharing options...
mahatma Posted October 16, 2004 Share Posted October 16, 2004 Yep, you're right ... Suffolk. Sorry 😳 Anywhere south of Birmingham is all the same to me Andy Link to comment Share on other sites More sharing options...
Rob Walker Posted October 16, 2004 Share Posted October 16, 2004 You don`t always need to skim the head after porting. It depends on what pistons you are running ie the HC Accralites give more than enough compression without skimming. Just be warned you cannot put the metal back. Link to comment Share on other sites More sharing options...
Neil Williams Posted October 16, 2004 Share Posted October 16, 2004 Dave, I recently had a VVC head skimmed by company called RX Heaven (Horsham Engine Centre), in Southwater, Nr Horsham. I think they charged £35 ,and did the job in a day. Their number is 01403 734666. They even said nice things about my porting work... Neil Link to comment Share on other sites More sharing options...
Dave McCulloch Posted October 17, 2004 Author Share Posted October 17, 2004 Rob I've cleaned up the combustion chambers and unshrouded the valves, which will have dropped the CR slightly. I'll also be running Omega pistons. My understanding was that the combination of these 2 would require a 10 thou skim. If I'm wrong on this, please SHOUT before it's too late - particularly given the time I spent porting the head Thanks Dave Link to comment Share on other sites More sharing options...
mahatma Posted October 17, 2004 Share Posted October 17, 2004 You could measure the volume the head to determine your CR. I seem to remember that the pockets in the pistons measure something like 2.8cc and you can measure the piston to deck height. That way you could work out exactly what needs skimming for your desired CR. This would be my approach, if working on my own engine (I learned the hard/expensive way). Alternatively, conventional wisdom suggests that a skim could be in order after some material removal from the combustion chamber. Andy Edited by - mahatma on 17 Oct 2004 13:41:24 Link to comment Share on other sites More sharing options...
Rob Walker Posted October 17, 2004 Share Posted October 17, 2004 If the gasket face is in good unmarked condition I would be reluctant to skim the head. In any case .010" is not going to make a lot of difference to the C/r. On the first K head that I ported I did not skim the head following work unshrounding the valves and cleaning up the combustion chambers. It was a standard head fitted with 29.5mm inlet and 26 mm exhausts, 285M or 740 cams and standard pistons on a 1600cc it made 186bhp. The engine is pictured LF and on Dave Andrews web site. The head was later sold to Dave Jackson who fitted 1227 cams and accralite pistons to increase CR it made a stonking 206 bhp out of 1600cc. Dave won the 2003 L7 speed championships with this engine. Link to comment Share on other sites More sharing options...
EFA Posted October 17, 2004 Share Posted October 17, 2004 Dave, Quality Engineered Products 25 Junction Rd, Burgess Hill, West Sussex RH15 0HR 01444 243720 Did work on my head earlier this year. A bit slow, but v.good IMO. Don't use BDS in Smallfield - Thery are to$$ers. Link to comment Share on other sites More sharing options...
Dave McCulloch Posted October 17, 2004 Author Share Posted October 17, 2004 Thanks for the replies. The head is brand new and hence the face is in good condition. I've just done some rough calculations and (if my maths is right ❗) and based on a guessed 7cm cylinder diameter and 10:1 CR, I reckon that a 10 thou skim would raise the CR to 10.2 - not huge, but should be enough to reverse the change in CR which must have arisen from the work on the combustion chamber. It will also ensure I have an absolutely flat head to start with. Dave Link to comment Share on other sites More sharing options...
mahatma Posted October 17, 2004 Share Posted October 17, 2004 Dave, Assuming Head comb chamber vol = 31.5cc Bore= 8cm Stroke = 8.93cm Displaced Vol = 448.9cc Gasket thickness = 0.15cm Gasket bore = 8.2cm Gasket Vol = 7.92cc Piston - deck height = 0.2cm Piston - Deck Vol = 10.1cc Piston Pocket Vol = 2.8cc CR = (31.5 + 448.9 + 7.92 + 10.1 + 2.8) / (31.5 + 7.92 + 10.1 + 2.8) CR = 9.6:1 If you take 10thou off your head = 0.0254cm This is about 1~1.3cc; Therefore, with a 10thou skim (assuming 1cc); CR = (31.5 + 448.9 + 7.92 + 10.1 + 2.8 - 1) / (31.5 + 7.92 + 10.1 + 2.8 - 1) CR = 9.7:1 There may well be a flaw in the calculation and it depends on your piston-deck height, the pocket volume of your pistons and the volume in your head but it looks about right to me. Ultimately, I'm sure that if you follow the advice of someone like DVA or Rob, you won't go far wrong. Andy EDIT : there was a fatal flaw in the calculation, now updated. Edited by - mahatma on 18 Oct 2004 20:11:59 Edited by - mahatma on 18 Oct 2004 20:14:07 Link to comment Share on other sites More sharing options...
Dave McCulloch Posted October 18, 2004 Author Share Posted October 18, 2004 Andy Agree with all the above except the effect of the skim. 10 thou is 0.0254cm which, based on an 8cm bore, gives a volume reduction of 1.3cc. Or have I got it wrong? Dave Link to comment Share on other sites More sharing options...
mahatma Posted October 18, 2004 Share Posted October 18, 2004 Wow, I was just editing that and you posted before I finished. Andy Link to comment Share on other sites More sharing options...
Dave McCulloch Posted October 18, 2004 Author Share Posted October 18, 2004 Andy Spooky! So does 0.1 CR make much of a difference?? Dave Link to comment Share on other sites More sharing options...
mahatma Posted October 18, 2004 Share Posted October 18, 2004 I believe not. I actually think that 10.2:1 is rather low anyway. Sorry for the calc errors too, I should have known better. I went through a similar exercise about 6 months back due to problems with a dodgy head that I bought. Ended up buying a new one off Tom and the engine's been great ever since (apart from lunching my clutch !) Andy Link to comment Share on other sites More sharing options...
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