GX390rebuild/mild port polish w/billet BEEF

sassycat

after the first run hr on a motor i got elsewhere "gx390" and i dont feel i was told the truth,or either i went past 3600 rpm,s a time or 2 but i didnt run it hard at all really...
changed the oil and the engine started a knock very slightly..the 1 hr oil looked very bad with metallic bad things that told me the story
the knock got worse fast just running it a few times in disbelief..the lil motor had way more power than i expected but was knocking..

ordered today from vegascarts.com,, one of our sponsers..jeff took the time 2 different occasions to talk motors and never acted like he was too busy for the questions i asked,and a very nice fella that seems to no what he is talking about for sure..
after telling him i wanted my stock motor to be reliable and rugged with a few better parts,and mainly i wanted a billet rod for the fact that im a chevy guy,and the thought of having a rod"bearing"only makes sense to me..

i would have spent more on roller rockers but all i was looking to get out of this engine was to LET IT SPIN in the upper rpm range from time to time..
so,heres what i ordered today
from jeff'
arc billet rod"will have to clearance crank and balance shaft iirc to fit in engine" will get pics
1.3;1 rockers
a 4 and 8 degree timing advance key
32lb springs
he even threw in hardened lash caps and told me the stock intake valve iirc did not have one and would wear the un hardened valve tip..he was right as i seen it was not there when removing rockers..THANKS JEFF

then i ordered from diffrent places and ebay and amazon because i needed to save money and thats just life,,sorry..
piston and ring set with wrist pin and clips
stock carb gasket set"ive already hogged the jet out a lil"
engine gasket set with extra head gasket and lots for 13 bucks,,could turn it down and was from same maker as others.
engine oil seals
new helix for my driven clutch thats worn into the screws
new ramp buttons
1 clutch bolt
1 clutch washer..i needed these for a while now.

went out a while ago and went ahead and drained the new fresh oil with nothing but 5 min run time and was nasty already..i had glued a magnet on the oil drain plug and there was lots of goodies stuck to that magnet..glad i glued it there i guess.

got the clutch off
the fan cover off
pulled the head and the lifter noise i been hearing that was so bad was prob the pushrod being bent pretty bad on the exhaust valve..the intake isnt perfectly straight either..was that way when i got it as i keep check on valve lash and such.

the piston looks new like the guy told me but it says yamamoto lol..this may be normal,i have no clue..seems to have to much side cleaeance in the piston wall to me also,,but it all looks very good and fresh like he said..

my oil does have a slight gas smell???? i just now got it getting enough gas to run as good as it was which was very good actually,but i smell gas in the block..is this normal??




the upper push rod is the one bent the worse,,it wont even roll..need bette than stock ones now for this build..


cylinder wall look good but i will check size and re hone it for the new piston


this is how the intake loos on a stock head..not bad but i will clean it up soon


the combustion chamber looks very clean and smoth as is but i will clean it up a lil also,and index the spark plug..and re lap the valves as ive always kinda liked lapping


when im done i could be in the 20hp range and the engine should cruise 4000 or better rpm,s for longer periods and be able to go to 5500 now and then and be safe..i wont press my luck and if needed i will cam it out in the future and get them roller rockers..
thats all for now..parts will start coming in saturday but prob next week before i will get started..but i may feel froggy and have to get inside the case to have a look.
yall come back now ya hear,,br549 over and out

BGW

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ORTitan

Sassy,

Can you get a picture with at different angle on the cylinder wall with the piston down?

In the picture you posted there are funny marks on the cylinder wall. I can't quite tell if it is oil film or the tattle tale of water etching.

Look like maybe some verticle scoring also.

sassycat

its oil..i wiped it out the bottom edge before the pic..but will take more tomorrow
i did notic while warming the engine to drain the oil today there was water dripping from the exhaust but i figured it was from condensation maybe?

sassycat

just ordered chromoly 6.5mm pushrods" 6.54 long " and a billet pushrod guide plate from nrraceing.com

sassycat

well i was wrong,the piston wall does have a few marks..there smooth and feel like they will hone up fine i hope .

the guides feel great and the valve seals look in great shape.the exhaust valve spring was very tight compared to intake spring,and sits lower in the pic,,guess this is normal as the valves look the same length.


timed the marks before tear down and im really confused lol..ive seen pics and it was simple looking..not my luck..the marks are lined up on the cam and crank but the balance shaft was almost 1/2 turn out??WTF
IS THIS POSSIBLE?? it ran super good just had a knockit did not feel un balanced either,,check out the marks


if i line up the balance shaft with crank the cam mark is off? so,i feel this small gear on the crank must be alighned wrong or? or is it made as part of the crank?anyone


here was the rod knock,,i could be wrong but i feel it was over tightened w/out torque wrench because the top rod bolt i had to hit with 5 lb hammer to break it loose..i found a 1/16th small piece of metal in the block that may have done this as it would match the crank marks kinda.
the worn rod measures 1.418 and the crank measures1.410 or 1.411..with cheap dial calipers that work fairly good..thats only 7-.008 oil gap and id think that was pretty good but have not researched it yet


the good side of the crank


the not as good sidestill need to find out the crank journals factory size.


the empty case..im pointing to the governor shaft that will be removed..maybe thats where the tiny metal part came from,but it looks in perfect shape


the other part of the gov that will be removed


will compare this piston to the new one and decide which one to use..
or i will just have another man cave trinket

sassycat

i have not researched this yet but i have no clue yet,,as to what this cam with spring,riding on the cam could be lol..looks like weights from the distributor of my old chevy anyone else


the head is in my room in the house and just got it all apart so i can clean up the factory left overs lil bit..
will remove gov shaft and oil sensor tomorrow and plug holes..

i read you can use a water temp gauge in the oil for oil temp..i wondered if it would work in the oil sensor hole where the wires come thru the block?
prob not as it wouldnt be in the oil i guess

sassycat

did a lil measuring and heres heres how its looking
cyl bore is 3.465 dead on close for my calipers,,checked many times also.
crank journal measures1.410 but will double check again..i think it shoulkd be
1.417 iirc..
the worn rod measures 1.418 so im doubting the 1.417 crank journal size is correct.
piston to bore clearance is .005 and looks correct as the piston skirt is 3.460.

dang i can never get a easy way out lately will have to wait to get the arc rod measured but i think i will be needing a new crank..
at this rate i could have 2 new 460cc clone engines complete shipped to my door

sassycat

well you guys are no help

the piston in the pic is installed wrong so you guys are slackin worse than me
according to the service manuel the piston should be installed with the triangle to the bottom of the head..its backwards lol..not from me..
if you cant tell im very miticulas about things some wouldnt care about,and every time i go to fix something it ends up being all new in the end because i cant leave things that are wrong,as is in an engine that is gonna waste the mulla ive spent in the long run if i cheese out to do it half azz

so then i find the exhaust valves on gx390,s has a factory hardened lash cap on the exhaust valve only..and a "rotator washer"under the spring on this valve only..
the previous owner had the lash cap on the intake valve with the wrong retainer holding it in i sometimes wish i wasnt mechanically inclined as maybe my luch would be better if i couldnt fix it
no biggie,,it will be right in the end

also found the weights and arm on the cam is called" decompressor weight" must be for when you let off the gas fast"maybe"

now i find the rod to be perfect in size even tho its bad and scared up..its still
1.418 which is standard size rod journal..so the guy installed the bad crank with a new rod to sell it and save his time and cash"in america we cal this a scum bag iirc
thats ok,im good at fixing others mistakes lately..i think this is what i was put on this earth for lately

so now i will have a wait a week maybe till i can order a new crankshaft..
i would have never thought the rod to crank pin clearance is only a couple thousandths..but its nice to think the motor will be good for a while after its done..
to top it all off my crank was turned to 7/8 shaft and i have a taperd clutch adapter for it..
the new crank will have a 1 inch keyed shaft and i will need a new tapered sleeve adapter so the price just keeps climbing
can never be sold now,,its gonna have to be a keeper

sassycat

just got some brownie points from the wife and she let me order a new crank should be here mon or tues.
ordered the tapered clutch shaft adapter from cartpartsplus.com

sassycat

WOW,thanks geoff at vegascarts.com..got the order in less than 4 hrs..i never expected it till next week...seems faster shipping than im used to lol.
i was supossed to get 1.3;1 stamped rockers,but he sent me shaft rockers.
which is what i wanted but he said he was out..they must have gotton them in before he shipped my order? but im happy
these arc rods gleem with quality..i love the oil dipper and its function..and really love all the oil holes in the rod sweet.