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Thread: Guide: How to build a K series motor

  1. #1
    Junior Member Too Much Toyota oldcorollas's Avatar
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    Aug 2005

    Default Guide: How to build a K series motor

    Because this topic comes up again and again, typically for people who are just starting to get into car modifying.. 'cos lets face it, corollas are the bottom of the pile

    so you want to build a K motor??

    the different blocks are K, 3K, 4K, 5K and 7K.

    I will focus on 3K/4K with a little on 5K's

    ---3K and 4K have same size pistons (75mm) !! if you have the original Repco/Toyota pistons, ditch them for ACL brand or better. cheap in 20, 40 or 60 thou oversize.
    some 4K pistons are dished. all 5K pistons are dished. 5K has bore of 80.5mm.

    ---4K has longer stroke (73mm) than 3K (67mm?). 4K also has taller deck height than 3K by about 10mm.

    --- 4K crank is IDENTICAL to 5K crank. 5K block is same deck height as 4K, but bigger bores. Apparently 3K and 4K blocks can be bored by 3-4mm, but you may be taking your chances due to core movement during casting.

    So lets start with a 4K block.... we bore it out 40thou for new ACL pistons, then what...
    starting from the bottom.

    in a budget build, chances are you won't want to do anything to the sump... a crank scraper or a windage tray would be a good idea tho.

    oil pumps. there are 2 or 3 different types. early type had a bolt on pickup, later types have the pickup as part of the lower housing (the bit that keeps the gears in).

    K series oil pump gears are SAME diameter as T and R series pumps!!! most T series have the SAME HEIGHT as K series, so they are no improvement. R series (and possibly 3TGTE) pumps have taller gears, and are possibilities for making a high flow pump for a K series..

    you can increase oil pressure a bit by putting a 2 or 3mm spacer behind the pressure relief valve spring )that hangs off the side of the PUMP.. not the oil filter )

    Cranks are fairly well balanced from factory, but if you are going to high rpm often, you may want to have it checked.

    Rods are not too bad. DEFINITELY have them checked for balance, they may be a long way out. Replace rod bolts with either new toyota ones, or something a bit more heavy duty. check balance end to end, and also total weight.

    pistons, as before.. check balance of pistons plus pins.

    Cylinder heads.
    from K to 4K (non-dished) the difference is mainly in the combustion chamber sizes and intake ports. exhaust ports seem to be pretty much the same across the board.. all too small. for intake ports, there are some tiny 25mm diameter ones... normal size is 27mm diameter and the bigports are 30mm diameter. i honestly don't think there is much benefit to going to a bigport head on a street driven motor...

    but anyway, bigports are available from K engines (22010) or from early 3K engines (24010). they can both be identified by the welch plug at the back of the head instead of a bolted on plate. it's a good idea to have this hole covered with an alloy plate and TIG'd so it will never leak.

    if you are building a 4K, then you will want a 3K head. simple reason is it has a 3ml smaller combustion chamber so you get a free increase in compression!!

    regardless of which head you get, port the walls and roof of the exhaust port, and clean up the bowl and short radius area. you can chamfer the new valve guides while you are there and shape the bosses in the port.
    intake ports just need a clean up and blending of the bowl and short radius.

    combustion chamber. remove all sharp edges and DESHROUD THE VALVES. aim for maximum deshrouding at mid valve lift. stock is about 2mm gap... i like about 5mm gap all the way around the valve.

    camshaft. this all depends on what rpmrange you want your power band, and if you are using EFI or a carby. EFI will lower the rpm at which the cam comes on and broaden the effective rpm power band. 230/[email protected] thou lift with 435thou lift is a Camtech 609 (adv 275/284)... a good cam that comes on around 3500-4000 and keeps going to about 8000,
    most people will want a little less.. sayyy, 220/[email protected], but high lift is always good 430-450thou lift is abotu as far as you want to go perhaps.

    over about 400-420 thou lift will require new valve springs (CB4/CB4A from performancesprings in QLD, or FJ20 springs also fit). valve retainers will typically need to be slightly modified to widen the seat area for the inner spring if using dual springs.

    cam towers. early ones are alloy and are taller, whilst later (most of them) are cast iron/steel and they are a few mm shorter. the rocker shaft position is the same for both, but toyota changed to the cast iron to reduce changes in valve clearance with temp.
    just use the later ones...

    if you are using a cam with higher lift than stock (about 8.5mm) GET THE ROCKER TOWERS MACHINED DOWN BY THE INCREASE IN LIFT.
    ie, 11mm lift cam = 2.5mm off the rocker towers.
    this maintains original rocker geometry when they are loaded the most, and reduces both noise and wear... i can't recommend this enough.

    choose a rocker shaft that is not too worn. you can flip them over and use them upside down (make sure the oil holes line up) but if they are too worn, you will lose oil pressure from between the rockers and the shaft.. not good.
    there are slight differences in rockers between engines, but not enough to worry.

    valves, rockers, rocker shafts and rocke towers will change between the different heads.

    of special note is that early heads have a different retainer, as the valves have 2 grooves, one of which is for an oil control o-ring above the valve lock. these retainers severly limit potential valve lift increases, so if you want to run high lift, swap to single groove valves and retainers (and change guides to ones with a groove to accept valve stem seals.

    rocker cover. very early have no PCV fitting...

    head gasket. i use ONLY ACL monotorque BD950MT.. no point stuffing around with any cheapers ones

    timing chain. all early models have twin row chain. later 4K's have a single row. going to higher lift cam/heavier springs? use the twin row. you can buy new sprockets, chains and guides... it is a good idea to swap them all over at the same time.

    hmmm.. early engines use a different width ran belt, so check you have the right pulleys.

    there are a few different water pumps depending which heater hose routing was used.. get whichever suits your needs. they have different lengths of shaft ont he front, and also different bolt spacing for the fan, so be careful.

    early alternators are denso, 25amp... then later 30amp or so...
    get KE70 BOSCH alternator (need top and bottom brackets also). they are better, higher amperage, and you can swap the guts of ford falcon 60A alternators into them (with longer bolts and altered rear bracket). they are also internally regulated, so you justneed 3 wires instead of the original 7.

    fuel pump.. block it off and get a cheap elec pump..

    dizzy. early denso have "octane selector" good for modifying base timign easily. also adjustable for vac start and stop...
    later are not so adjustable and Bosch dizzies also have larger cap.

    sparkplugs. NGK BP5EY or BP5ES. for modded motor, BP6EY is a good start. you couldn't need to go colder.

    ummm.. exhaust manifolds. 4-2-1 pipe sizes about 37-43-50, lengths 45-45-90cm before first resonator. 2" pipe, biggest chamber reverse flow muffler at the back in 2" will be plenty and still quiet.. cannons suck

    intake... early straight runner and later curved runner manifolds both suck as they go down to maybe 25mm internally. they can both be used, and require an adaptor to bolt up to weber carbs.

    the 32/26 ford weber is a BAD choice. the chokes are too big.
    go for something like a euro weber (Fiat etc) with a primary choke around 22-24mm and secondary choke around 27mm. a 34DMS is a good start, but maybe a little big (24mm choke)

    if possible, go EFI using a 4KE or 7KE manifold they are MUCH better than the downdraught manifolds, and control it with a cheap Megasquirt. Thats another story.

    what else...
    early motors have tiny clutch. later models have bigger clutch.. use that... all the flywheels are pretty similar and heavy.. resist the temptation to lighten the stocker and go for an aftermarket alloy or steel one.

    so endeth part 1 of the K lesson ;

    Cya, Stewart
    "I'm a Teaspoon, not a mechanic"
    "There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)

    AU$TRALIA... come and stay and PAY and PAY!!! The moral high horse of the world!

  2. #2
    Junior Member Too Much Toyota oldcorollas's Avatar
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    Aug 2005

    Default Re: Guide: How to build a K series motor

    regarding the difference between early (K and 3K bigport) and late (everything else) Valves and Valve Retainers.

    The 3K BP has a taller retainer, so can't have as much lift, can't run dual springs, and has an O-ring seal. Consequently, the 3K valve has TWO GROOVES, and can't be used with the 4K retainer (well it can, but it doesn't help you.. it just reduces spring bind height). there is no valve stem seal, instead the top valve groove has an O-ring that seals between the retainer and the valve stem. The valve guide has no groove to locate a seal even if you put it on there.

    The 4K's have a thinner retainer, which can run higher lift and dual springs. The valves also have a single groove (for the lock). The dual groove retainer can't be used with the single groove valves, as the rocker will foul on the retainer. There is a valve stem seal on the valve guide, and the valve guide has grooves to locate the seal.

    AFAIK, the valve locks are identical betweeen models.

    "I'm a Teaspoon, not a mechanic"
    "There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)

    AU$TRALIA... come and stay and PAY and PAY!!! The moral high horse of the world!

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