sean01
Legend Spanner Spinner
Ok been thinking of doing a run through of the KLX style YX engine top end build process.
this will also include a few little hot up and reliability mods.
ok well firstly you'll want to drain the oil out of the engine so you don't make too much of a mess.
parts/materials needed..
top end gasket set (inlet manifold gasket, exhaust gasket, head gasket, cam gear gasket and maybe a base gasket)
piston kit
engine oil
really good sealant like Honda bond or high quality high temp silicon
degreaser of some sort and also strong truck wash
WD40
rags
tools needed..
8mm, 10mm, 12mm, 14mm, 17mm sockets and extension bars.
8mm, 9mm and 10mm spanner
possibly you'll need some allen keys(hex keys)
impact driver with star(Philips) screw driver bit
hammer
pointy nose pliers
variety of screw drivers
gasket scraper or Stanley knife blade
honing tool
variable speed drill
air compressor and air blower
bench vise
depending on the bike style you have, remove what ever appears to be in the way of the head coming off.
start by removing the inlet manifold, exhaust pipe and spark plug.
then remove the magneto cover and the cam gear cover and just crack the bolts that hold the valve covers on.
with a 14mm socket stop the magneto from turning while cracking the cam gear bolts.
once there loose roll the magneto till you have TDC on the cam(usually the mark on the cam gear with YX stamped). TDC on the cam is timing mark @ 9 o'clock (there is a arrow cast into the head).
now with a 10mm socket or spanner remove the bolt in the center of the timing chain adjuster. now remove the timing chain adjuster all together.
double check to see it is still on TDC and remove the cam gear bolts all together and pull the cam gear away from the camshaft.
now if your replacing the camshaft now is the time to undo the 2 screws in the camshaft retaining plate with an impact driver. remove the retaining plate completely.
on the opposite side of the engine remove the oil feed pipe from the clutch cover and the head.
undo the 4 head bolts(take note of where the brass washer is).
remove the 2 long bolts from inside the cam gear area(they screw into the cases from the head).
the head will now slide away from the barrel (may need a bit of prying)
at the moment your engine should look like this
to remove the barrel you will need to remove the 2 bolts that hold the bash plate to the barrel.
pull the bottom rubber chain guide out of the barrel.
now slide the barrel off (may need a little prying)
if your replacing the piston then start by removing the wrist pin clip from the clutch side (cam chain guide is in the way on the other side), then slide the wrist pin out (this may need a small screw driver)
and there you have it, complete top end removed and ready for cleaning, modding/prepping and assembly.
start with cleaning all gasket surfaces till there is no signs of the gasket at all.
give the barrel a quick wipe out with a rag.
fit the barrel in a vice, but don't clamp it on any gasket surfaces.
now with the drill fitted with the honing tool give the barrel a good spray with wd40.
start with a reasonable speed on the drill and start honing it, but always keep the hone going up and down the barrel.
also make sure the hone isnt chattering, if so then apply more pressure on the hone with the adjuster.
when your happy that there is no or minimal marks in the barrel lower the speed of the drill a pretty slow speed.
now this going to be the finishing hone and can be a little tricky. give the barrel another good spray with wd40.
start the hone and go straight to the opposite end of the bore..pull the trigger on the drill, get to the bottom and release the button then the same when coming back up the bore. do this several times then squeeze the hone legs in and remove the hone form the bore.
give it a spray and wipe it out and check out the finishing pattern, you want a nice even 45 degree crosshatch in the bore.
(hard to see in the pic but it is evident)
when your happy with the finish give it a good degrease then a good wash with HOT soapy water and another degrease. blow dry the barrel completely as it only takes minutes before rust will form.
use a tissue and wipe the bore out to make sure no dirt or grit is left in it..
ok barrel finished spray the bore with WD40.
if your porting the head now is the time to do it, for a simple clean up job you can leave the valves intact.
iv found the best and easiest porting for these is to open the exhaust port up to the exhaust gasket and same with the inlet.. just blend what you have removed back to the guide boss.
probably not a bad idea to do a leak test on the valves.
1 port at a time fill with water, kero or fuel and make sure the valves aren't weeping/leaking.
if they are then they will require work (re-lapping in or re-machining)
for cleaning the head i recommend you remove the camshaft.
to do this remove the valve covers completely and loosen the valve adjuster screws a little bit.
now the camshaft retaining plate should be removed already so from where the plate was you'll see 2 round shafts, these are the rocker arm shafts.
use a 8x1.25 threaded bolt (commonly 12mm/13mm head), screw it in to one shaft at a time and pull them out.
now remove the rockers from the head. now the cam can slide right out.
again clean all gasket surfaces and clean the head with degreaser then a quick wash with truck wash and blow dry and spray with WD40.
now for installing the piston and rings or just rings...
start with the center oil ring first then the bottom outer ring and then top outer, then install the second ring then the top.
space all the ring gaps 180 degrees apart except the center oil ring which will be 90 degrees from both the outers.
the black ring goes in the second ring groove and the chrome ring in the top.
if there are any marks or letters on the rings, they always face to the top of the piston.
install the cam chain side wrist pin clip, these can be tricky and can get lost easily when they slip.
now slide the piston over the con-rod, on the piston there should be some letters (EX on this one) that goes to the exhaust side of the engine. so facing down.
oil the wrist pin and slide it in from the clutch side then install the last wrist pin clip.
apply some oil to the piston and rings and dab it around making sure all the piston is coated (except the top).
for the base gasket, you can choose to either install the proper gasket or leave it out and apply some silicon gasket sealant.
using sealant increases your compression a little by raising the piston up the bore(by approx 1mm).
also when using sealant make sure the case and barrel gasket surface is totally free from any oil.(clean with a bit of fuel)
you can see the difference in the following picture. and don't go over board with the sealant.
ok now you ready to install the barrel. firstly make sure both the locating dowels are installed to either the cases or the barrel.. should be 2 on the cam chain side
slide the barrel down and slowly work the rings into the barrel. the bottom of the bore is tapper-ed and usually closes the ring gaps on its own. if it feels stuck, remove and try again. on occasions i have had to use something to help close the gaps but be careful not to damage the rings..
installing the head is pretty straight forward. but don't forget to install the bottom cam chain guide in the barrel and also the dowels, and the cam gear @ TDC with the crank @ TDC before fitting the head.
this will also include a few little hot up and reliability mods.
ok well firstly you'll want to drain the oil out of the engine so you don't make too much of a mess.
parts/materials needed..
top end gasket set (inlet manifold gasket, exhaust gasket, head gasket, cam gear gasket and maybe a base gasket)
piston kit
engine oil
really good sealant like Honda bond or high quality high temp silicon
degreaser of some sort and also strong truck wash
WD40
rags
tools needed..
8mm, 10mm, 12mm, 14mm, 17mm sockets and extension bars.
8mm, 9mm and 10mm spanner
possibly you'll need some allen keys(hex keys)
impact driver with star(Philips) screw driver bit
hammer
pointy nose pliers
variety of screw drivers
gasket scraper or Stanley knife blade
honing tool
variable speed drill
air compressor and air blower
bench vise
depending on the bike style you have, remove what ever appears to be in the way of the head coming off.
start by removing the inlet manifold, exhaust pipe and spark plug.
then remove the magneto cover and the cam gear cover and just crack the bolts that hold the valve covers on.
with a 14mm socket stop the magneto from turning while cracking the cam gear bolts.
once there loose roll the magneto till you have TDC on the cam(usually the mark on the cam gear with YX stamped). TDC on the cam is timing mark @ 9 o'clock (there is a arrow cast into the head).
now with a 10mm socket or spanner remove the bolt in the center of the timing chain adjuster. now remove the timing chain adjuster all together.
double check to see it is still on TDC and remove the cam gear bolts all together and pull the cam gear away from the camshaft.
now if your replacing the camshaft now is the time to undo the 2 screws in the camshaft retaining plate with an impact driver. remove the retaining plate completely.
on the opposite side of the engine remove the oil feed pipe from the clutch cover and the head.
undo the 4 head bolts(take note of where the brass washer is).
remove the 2 long bolts from inside the cam gear area(they screw into the cases from the head).
the head will now slide away from the barrel (may need a bit of prying)
at the moment your engine should look like this
to remove the barrel you will need to remove the 2 bolts that hold the bash plate to the barrel.
pull the bottom rubber chain guide out of the barrel.
now slide the barrel off (may need a little prying)
if your replacing the piston then start by removing the wrist pin clip from the clutch side (cam chain guide is in the way on the other side), then slide the wrist pin out (this may need a small screw driver)
and there you have it, complete top end removed and ready for cleaning, modding/prepping and assembly.
start with cleaning all gasket surfaces till there is no signs of the gasket at all.
give the barrel a quick wipe out with a rag.
fit the barrel in a vice, but don't clamp it on any gasket surfaces.
now with the drill fitted with the honing tool give the barrel a good spray with wd40.
start with a reasonable speed on the drill and start honing it, but always keep the hone going up and down the barrel.
also make sure the hone isnt chattering, if so then apply more pressure on the hone with the adjuster.
when your happy that there is no or minimal marks in the barrel lower the speed of the drill a pretty slow speed.
now this going to be the finishing hone and can be a little tricky. give the barrel another good spray with wd40.
start the hone and go straight to the opposite end of the bore..pull the trigger on the drill, get to the bottom and release the button then the same when coming back up the bore. do this several times then squeeze the hone legs in and remove the hone form the bore.
give it a spray and wipe it out and check out the finishing pattern, you want a nice even 45 degree crosshatch in the bore.
(hard to see in the pic but it is evident)
when your happy with the finish give it a good degrease then a good wash with HOT soapy water and another degrease. blow dry the barrel completely as it only takes minutes before rust will form.
use a tissue and wipe the bore out to make sure no dirt or grit is left in it..
ok barrel finished spray the bore with WD40.
if your porting the head now is the time to do it, for a simple clean up job you can leave the valves intact.
iv found the best and easiest porting for these is to open the exhaust port up to the exhaust gasket and same with the inlet.. just blend what you have removed back to the guide boss.
probably not a bad idea to do a leak test on the valves.
1 port at a time fill with water, kero or fuel and make sure the valves aren't weeping/leaking.
if they are then they will require work (re-lapping in or re-machining)
for cleaning the head i recommend you remove the camshaft.
to do this remove the valve covers completely and loosen the valve adjuster screws a little bit.
now the camshaft retaining plate should be removed already so from where the plate was you'll see 2 round shafts, these are the rocker arm shafts.
use a 8x1.25 threaded bolt (commonly 12mm/13mm head), screw it in to one shaft at a time and pull them out.
now remove the rockers from the head. now the cam can slide right out.
again clean all gasket surfaces and clean the head with degreaser then a quick wash with truck wash and blow dry and spray with WD40.
now for installing the piston and rings or just rings...
start with the center oil ring first then the bottom outer ring and then top outer, then install the second ring then the top.
space all the ring gaps 180 degrees apart except the center oil ring which will be 90 degrees from both the outers.
the black ring goes in the second ring groove and the chrome ring in the top.
if there are any marks or letters on the rings, they always face to the top of the piston.
install the cam chain side wrist pin clip, these can be tricky and can get lost easily when they slip.
now slide the piston over the con-rod, on the piston there should be some letters (EX on this one) that goes to the exhaust side of the engine. so facing down.
oil the wrist pin and slide it in from the clutch side then install the last wrist pin clip.
apply some oil to the piston and rings and dab it around making sure all the piston is coated (except the top).
for the base gasket, you can choose to either install the proper gasket or leave it out and apply some silicon gasket sealant.
using sealant increases your compression a little by raising the piston up the bore(by approx 1mm).
also when using sealant make sure the case and barrel gasket surface is totally free from any oil.(clean with a bit of fuel)
you can see the difference in the following picture. and don't go over board with the sealant.
ok now you ready to install the barrel. firstly make sure both the locating dowels are installed to either the cases or the barrel.. should be 2 on the cam chain side
slide the barrel down and slowly work the rings into the barrel. the bottom of the bore is tapper-ed and usually closes the ring gaps on its own. if it feels stuck, remove and try again. on occasions i have had to use something to help close the gaps but be careful not to damage the rings..
installing the head is pretty straight forward. but don't forget to install the bottom cam chain guide in the barrel and also the dowels, and the cam gear @ TDC with the crank @ TDC before fitting the head.
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