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Car Forum / MINI / August 2003Engine rebuild
Hello, I'm rebuilding my 1275GT engine at the moment and want some ideas on how to proceed, it is am A series with approx 65000 miles on it. My plan is to rebuild to 1275 spec or at most 1293. I want a reliable motor and therefore plan to only tune mildly with a stage 1 kit. I have to add that I am a toolmaker and have access to many workshop machines and there fore intend doing most of the work myself if possible. My questions are as follows: Is it possible to leave at 1275 capacity and just replace the piston rings or will I have to rebore? ( I've visually checked the bores and they appear to be smooth with no scratched or wear evident, however I havent measured them.) at 1293 capacity. do I just need bigger piston rings or do I need pistons as well. How do I clean the oily muck off the block and head, and what will I spray metal with after wards, i.e. stove enamel, paint, red oxide??? How do I clean the internal tracks in the head/block head after removing all components. The block and head will have to be skimmed as the head gasket has blown between the middle two pistons, how much can I skim off and how is this done? surface grinder or milling machine fly cutter How do I cut new angles on the valve prior to replacement, I presume on a rotary fixture on a surface grinder or is there an easier way. Finally, what else should I do to the engine prior to reassembly. Also, the mating faces between the gearbox and engine are slightly marked, can I remove material and put in a gasket to ensure no oil leaks, or since its a mini, reduce oil leakage. Thanks Leon > Hello, > I'm rebuilding my 1275GT engine at the moment and want some ideas on [quoted text clipped - 13 lines] > they appear to be smooth with no scratched or wear evident, however I > havent measured them.) Check the lip at the top will show wear. I would replace the pistons and rings. The top groove wears as well as the rings hence you may break the new top ring if fitting new rings to old pistons. > at 1293 capacity. do I just need bigger piston rings or do I need > pistons as well. The bore size will dictate the ring size i.e. if its standard bore its std ring set - if its bored oversize its an oversize ring set - you don't put oversize rings into a standard bore. The pistons run at a clearance in the bore I think 0.003"-0.005" > How do I clean the oily muck off the block and head, and what will I > spray metal with after wards, i.e. stove enamel, paint, red oxide??? > How do I clean the internal tracks in the head/block head after > removing all components. I would be getting the block and head chemically cleaned so the oil gallery and water jacket are cleaned properly. Paint - you can buy engine enamel in a spray can or I use spraying enamel so that it can be mixed to the required colour and brush that on. > The block and head will have to be skimmed as the head gasket has > blown between the middle two pistons, how much can I skim off and how > is this done? surface grinder or milling machine fly cutter yes - mostly now days its a fly cutter - minimal off each just to clean them up. > How do I cut new angles on the valve prior to replacement, I presume > on a rotary fixture on a surface grinder or is there an easier way. take it somewhere to have the valves and seats machined as they will come back at the same and correct angle and seat better. > Finally, what else should I do to the engine prior to reassembly. > > Also, the mating faces between the gearbox and engine are slightly > marked, can I remove material and put in a gasket to ensure no oil > leaks, or since its a mini, reduce oil leakage. new gasket, o ring and good glue. > Thanks > Leon Below is a post I made to the Mini List a few months ago in response to a question about building your first engine. Given the nature of your questions I think this would be a good place to start. You will, of course, have to get the specs for the A-series engine that you are rebuilding. Cheers, Kelley When I first got interested in engine building I spent a lot of time looking for build information specific to the engine I wanted to build (Volvo B-20, in case you're interested). While there was a lot to be found regarding specifications there was little available regarding the general mechanics of how one builds an engine. After a lot of searching, this was pre-internet searching, I found that the best and only beginner books and articles were published for American V-8 hot rods. The only trick is learning what you can apply to a straight 4 and what to ignore. Even after all of these years I have yet to see a good basic beginner's book on rebuilding a 4 cylinder engine. With this in mind I did a web search and found a couple of good articles, obviously for short track racers, but good information nevertheless. http://www.circletrack.com/tipstricks/4624/ http://www.circletrack.com/tipstricks/4636/ The articles below cover more specific topics. http://racingarticles.com/article_racing-29.html http://racingarticles.com/article_racing-10.html The URL below looks good despite the constant NASCAR references. It gives some insight into planning engine builds for specific purposes. http://www.circletrack.com/techarticles/93459/ I hope these help. >Hello, >I'm rebuilding my 1275GT engine at the moment and want some ideas on [quoted text clipped - 38 lines] >Thanks >Leon > Hello, > I'm rebuilding my 1275GT engine at the moment and want some ideas on [quoted text clipped - 13 lines] > they appear to be smooth with no scratched or wear evident, however I > havent measured them.) In theory, you could hone the bores and fit new standard size rings...BUT Honing the bores will increase the piston-to-bore clearance, resulting in the rings having to work harder and finally a smokey or poor-performer in a shorter period of time compared to using new pistons (and rings) and bore to suit. > at 1293 capacity. do I just need bigger piston rings or do I need > pistons as well. New pistons, rings and a bore of the cylinder block. > How do I clean the oily muck off the block and head, and what will I > spray metal with after wards, i.e. stove enamel, paint, red oxide??? > > How do I clean the internal tracks in the head/block head after > removing all components. A machine shop will have tanks where the majority of the old crap can be washed out. However, it will still need a through clean before re-assembly - Never rely on just on the machine shops cleaning... You can use pipe cleaners, thin bottle/barrel brushes to get through the oil ways - Use paraffin or cellulose thinners soon shifts the muck too.. Poke and scrape the water-ways with an metal rod to get the sediment out too.... Paint the exterior of the engine with engine enamal > The block and head will have to be skimmed as the head gasket has > blown between the middle two pistons, how much can I skim off and how > is this done? surface grinder or milling machine fly cutter Skim of the minimum to get the head flat, use a milling machine. If your raising the static compression ratio then you can skim more off - though this may be a bit 'advanced' at this stage. Consider skiming the block face to get a true flat surface.. > How do I cut new angles on the valve prior to replacement, I presume > on a rotary fixture on a surface grinder or is there an easier way. I'd suggest a engine machine shop - also fit new valve guide before having the valve seats re-cut. > Finally, what else should I do to the engine prior to reassembly. Lots and lots.. Everything must be spotless - and everything must be checked and measured and where necessary corrected before final assembly... > Also, the mating faces between the gearbox and engine are slightly > marked, can I remove material and put in a gasket to ensure no oil > leaks, or since its a mini, reduce oil leakage. A gasket usually sits between the block and gear box. Dress any dings with a file or stone... I'd suggest that if you can, see if you can get the help of someone whos done it before.. HTH, Dave http://www.icklemini.co.uk |
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