Turbo Goose Posted December 2, 2014 Share Posted December 2, 2014 Hi guys I'm currently building a forged engine and unsure whether to get machine work done first or buy pistons/rods/beaeings firstThing is I dont know whether it needs a rebore or not. Cylinders are well within tolerance but are a bit marked up so not sure if i will need to buy 74 or 74.5mm pistons.Also not sure if the crank needs a grind, it hasnt spun a bearing or anything but a little marked.Do machine shops match the cylinders to the pistons oe simply rebore to 74.5mm if thats the size im getting. Same with shells do they need them first or just see if it needs a grind and do the crank 0.25 undersized?Hope that makes sense.So basically do i juat order oversized pistons and shells and get machine work to match. Or risk buying standard size and just get a hone/ crank polishWhat did you guys do? Quote Link to post Share on other sites
Socks Posted December 2, 2014 Share Posted December 2, 2014 Usually forged pistons come with a tolerance sheet. with all the toleranes the bores need to be bored/honed too. Go 74.5mm, be mad not too when spending a lot of money! You want it to be right! As for the crank, if it hasn't spun a shell. Get the tolerances checked on that too. If there good, get it micropolished... Clean the surfaces.... Quote Link to post Share on other sites
Turbo Goose Posted December 2, 2014 Author Share Posted December 2, 2014 Cranks within tolerances as well but its got marks on it but reckon ill get away with a polish hopefully! Quote Link to post Share on other sites
Phil Posted December 2, 2014 Share Posted December 2, 2014 (edited) Cranks within tolerances as well but its got marks on it but reckon ill get away with a polish hopefully! buy the moving parts first. (rods/pistons/cams/valves) Machine work second (bore/hone/skim/lap/grind) perishable bits third (seal/bearings/headgasket) and you wont go wrong. Phil Edited December 2, 2014 by Phil Quote Link to post Share on other sites
Turbo Goose Posted December 8, 2014 Author Share Posted December 8, 2014 Not sure what size bits to order yet though as they are coming from america so dont want to get it wrong! Suppose first thing to do is take my parts to machine shop and see if i will need oversized parts Quote Link to post Share on other sites
funny onion Posted December 8, 2014 Share Posted December 8, 2014 it's cheaper/easier to source another block/crank if you do buy the rods and pistons and bearings first then the machine shop tell you they are outside tolerances i suppose. but as above, if you go for 74.5mm pistons and give the spec sheet to the machine shop you know it will have been machined properly to spec... same with oversize bearings. I've been thinking about building a forged engine for a while but i'm sure people like taggy and turbo grant will be able to advise properly Quote Link to post Share on other sites
Phil Posted December 8, 2014 Share Posted December 8, 2014 (edited) Sorry I should have said that it would be my opinion that 74mm forgies are a waste of time.Therefore I would be ordering 74.5 in your case and working from there. it's cheaper/easier to source another block/crank if you do buy the rods and pistons and bearings first then the machine shop tell you they are outside toleranceYou take pistons rods to machineshopHe does machine work and then he can spec the bearings.See my first post for the correct orderPhil Edited December 8, 2014 by Phil Quote Link to post Share on other sites
Turbo Goose Posted December 8, 2014 Author Share Posted December 8, 2014 thanks for the help guys. Think ill just leave bearings off the shopping list from america and get the machine shop to source them.Going to order 74.5mm pistons right now! Quote Link to post Share on other sites
Phil Posted December 8, 2014 Share Posted December 8, 2014 thanks for the help guys. Think ill just leave bearings off the shopping list from america and get the machine shop to source them. Going to order 74.5mm pistons right now! its not that they would have to source them, more its just the order of doing things to insure you dont order something that wont fit. I dont know a machine shop yet who will say for certain that it will polish up, and order bearings based on that. they will polish it and then order you bearings. so if you ordering the bearings yourself even cheap from america then you should do the same, order after the crank is sorted. what you could do if the lead in time for bearings from america is long, take the crank and get it sorted first, and order your bearings. before you worry about pistons or rebore. spread the cost over time. Phil Quote Link to post Share on other sites
funny onion Posted December 8, 2014 Share Posted December 8, 2014 its not that they would have to source them, more its just the order of doing things to insure you dont order something that wont fit. I dont know a machine shop yet who will say for certain that it will polish up, and order bearings based on that. they will polish it and then order you bearings. so if you ordering the bearings yourself even cheap from america then you should do the same, order after the crank is sorted. what you could do if the lead in time for bearings from america is long, take the crank and get it sorted first, and order your bearings. before you worry about pistons or rebore. spread the cost over time. Phil Yeah when i took my crank in to park engineering, they measured it up and it was within tolerance on the main and rod journals but then after they polished it up they advised that it was still within tolerance but only just and said i would be better going for oversize bearings (they reground and polished again to suit the oversize bearings at a very good price as I was a bit put out as I ordered the standard bearings on their initial recommendation lol). Quote Link to post Share on other sites
Phil Posted December 8, 2014 Share Posted December 8, 2014 Yeah when i took my crank in to park engineering, they measured it up and it was within tolerance on the main and rod journals but then after they polished it up they advised that it was still within tolerance but only just and said i would be better going for oversize bearings (they reground and polished again to suit the oversize bearings at a very good price as I was a bit put out as I ordered the standard bearings on their initial recommendation lol). sound build advice saves money Lol Phil Quote Link to post Share on other sites
Taggy Posted December 10, 2014 Share Posted December 10, 2014 (edited) My honest advice on buying a forged engine after building one from scratch my self is to just buy one ready made from tuning developments or race tech. After i priced everything up, the price difference is hardly anything. By the time you buy all the parts and get the machine work done your gonna be topping well over £2k anyway, which is near enough what they charge, but the most important part is you get a warrenty and after sales support with the supplier which is worth 10 x the cost of the engine. Its too easy to miss somthing or make a minor mistake building it and the whole build can go down the pan, sorry to sound so negative its just what i thought in hind sight after mine. Save up some money and get a fresh built one Or if you do build one just make sure you take your time and check everything twice! Edited December 10, 2014 by Taggy Quote Link to post Share on other sites
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