Export thread

Need Advice, Blow by at carb on Fx801v engine

#1

R

rrh

Just purchased the mower with a blown engine. original owners ran it out of oil and wiped out the connecting rods and crank. I went ahead and installed new rings, rods, crank and of course seals and gaskets. I honed the block and before assembly. I did however assemble the block using assembly lube to ensure lubrication when first start. Anyway, getting to the point. The engine fired up fine but there is a lot of blow by through the carb. is won't rev up high and sounds like the timing is off. I tripled checked the timing marks on the crank vs the cam during assembly. I did notice the timing mark on the crank is a small arrow not a dot like the original crank. All parts were purchased from Kawasaki. Can anyone give me some advice on where to start or what to check.


#2

mhavanti

mhavanti

While you had the heads off, did you check the valves for sealing with some very light liquid such as toluene, gasoline, naptha, etc.? Did you grind the valves and seats and then make sure they were seating and sealing?

If the engine got hot enough, the valve springs may also have become annealed and lost 20% or more of their energy.

Here is how you can make a compression tool to hold the valves up while you replace valve springs. Break out the electrode and ceramic of a spark plug that fits the head. It can be any plug as long as it has the correct size threaded area and seating area. Whatever you air quick connect you use, place it against the spark plug base, weld it to the spark plug.

Then screw it into the spark plug hole, also, remove the hose to the fuel pump from the valve cover(s), place compressed air into the cylinder to test blow by from both the carb and oil filler tube. This will tell you if you have a valve leak and you will get some blow by out of the oil filler tube and valve covers as rings can't completely seal a cylinder.

Have fun and good luck,

Max


#3

R

rrh

I lapped the valves in using lapping compound, got a good ring on the seats there is about 3/16" wide lap looked really good. Also I forgot to mention when the motor was running I pulled off the crankcase breather hose (the one that plugs into the bottom of the carb. No Blow by. I didn't check valve leak by liquid test (my bag). and I didn't touch the carb during this rebuild. I have a compression tested so I can check the compression (just purchased it). I do that this weekend. I really hate to go back into the engine but may have to.

Thanks for your reply and advice


#4

mhavanti

mhavanti

rrh,

If you have a valve seat 3/16" wide, you're more than likely going to have a blow by. You only want 1/16" seat width as it will widen as it begins to wear in way down the road. It can seal much better and much less likely to grab any carbon from the fuel cooled engine in a narrow seat as the valves open and close they have a tendency to self clean. Wider the seat area, more likely you also need a stronger valve spring.

Do your compression check, you might also check the spring pressures on the seat as well as at full valve opening.

Do the compression tests first.

Max


#5

R

rrh

Again I'm sorry about mis information. My valve seats are more like 3/32" not 3/16" I typed the larger by mistake. I'll do a compression check this weekend. The one thing that stanks out to me was the comment about the exhaust seat moving when worn. I'll do another leak test before I come back with my findings. again thanks for the helpful advice.

RRH


#6

mhavanti

mhavanti

rrh,

Sounds good. Would like to see you back up to snuff soon.

Max


#7

B

bertsmobile1

mhavanti said:
While you had the heads off, did you check the valves for sealing with some very light liquid such as toluene, gasoline, naptha, etc.? Did you grind the valves and seats and then make sure they were seating and sealing?

If the engine got hot enough, the valve springs may also have become annealed and lost 20% or more of their energy.

Here is how you can make a compression tool to hold the valves up while you replace valve springs. Break out the electrode and ceramic of a spark plug that fits the head. It can be any plug as long as it has the correct size threaded area and seating area. Whatever you air quick connect you use, place it against the spark plug base, weld it to the spark plug.

Then screw it into the spark plug hole, also, remove the hose to the fuel pump from the valve cover(s), place compressed air into the cylinder to test blow by from both the carb and oil filler tube. This will tell you if you have a valve leak and you will get some blow by out of the oil filler tube and valve covers as rings can't completely seal a cylinder.

Have fun and good luck,

Max
Click to expand...

Alternate method is to feed about 3' of thin rope into the plug hole then wind the piston up to compress the rope against the head.


#8

mhavanti

mhavanti

Bert,

Always more than one way to skin a cat.

Max


#9

R

rrh

mhavanti said:
Bert,

Always more than one way to skin a cat.

Max
Click to expand...

Did a compression check 170 and 160 PSI


#10

G

geelee

think cam is out of time, pull 1 valve cover and plug . slowly rotate engine by hand. on the stroke that's not compression as the piston come up to top dead center one valve will close and other will open . this should happen right at top of stroke, if not cam is out of time


#11

R

rrh

geelee said:
think cam is out of time, pull 1 valve cover and plug . slowly rotate engine by hand. on the stroke that's not compression as the piston come up to top dead center one valve will close and other will open . this should happen right at top of stroke, if not cam is out of time
Click to expand...

That's my determination. I'm sure I lined up the marks. I did notice on the new crank there's not a dot like the original crank had but instead a small arrow. At the top of the of the exhaust stroke the exhaust valve closes and the intake valve opens at the same time (as per your response - I think). I look at that tonight, but my guess the crank is mismarked and i'll use your suggestion to assure the valve timing. thanks


#12

R

rrh

Found the problem. I dismantled the engine and basically inspected each part. I took the heads and preformed a leak test by pouring paint thinner into the combustion chamber and let it sir - no leak by. Then I split the case looking for timing marks I saw that I indeed matched the marks (the arrow on the crank to the dimple on the cam. But I wasn't convinced that was right. I pulled the old crank out of the metal scrap bin and inspected it. I found that the original crank timing mark lined up with the oil hole on the crank bearing shaft, but the new cranks didn't. I located the oiling hole on the new crank and looked at the tooth where the dimple should be and to the naked eye there was no dimple. I took a pick and rubbed the cranks teeth and found a very slight dimple on the correct tooth. pass along to your readers that be aware of replacement cranks (mine came direct from Kawasaki) the dimples may or may not be apparent. Thanks for all you guys help. Your thoughts and advice really helped me and I hope my findings can help someone else in need.


#13

R

rrh

geelee said:
think cam is out of time, pull 1 valve cover and plug . slowly rotate engine by hand. on the stroke that's not compression as the piston come up to top dead center one valve will close and other will open . this should happen right at top of stroke, if not cam is out of time
Click to expand...

Found the problem. I dismantled the engine and basically inspected each part. I took the heads and preformed a leak test by pouring paint thinner into the combustion chamber and let it sir - no leak by. Then I split the case looking for timing marks I saw that I indeed matched the marks (the arrow on the crank to the dimple on the cam. But I wasn't convinced that was right. I pulled the old crank out of the metal scrap bin and inspected it. I found that the original crank timing mark lined up with the oil hole on the crank bearing shaft, but the new cranks didn't. I located the oiling hole on the new crank and looked at the tooth where the dimple should be and to the naked eye there was no dimple. I took a pick and rubbed the cranks teeth and found a very slight dimple on the correct tooth. pass along to your readers that be aware of replacement cranks (mine came direct from Kawasaki) the dimples may or may not be apparent. Thanks for all you guys help. Your thoughts and advice really helped me and I hope my findings can help someone else in need.


#14

mhavanti

mhavanti

rrh,

Considering we're all going on the cam and crank were correctly timed. You received a lot of good advice that you followed before reassembling your engine. So, once you found the timing marks, indexed them properly. That rascal should run like a scalded ape now.

Glad you found your problem,

Max


#15

R

rrh

mhavanti said:
rrh,

Considering we're all going on the cam and crank were correctly timed. You received a lot of good advice that you followed before reassembling your engine. So, once you found the timing marks, indexed them properly. That rascal should run like a scalded ape now.

Glad you found your problem,

Max
Click to expand...

Again thanks, Seams like I have another problem. The motor don't seam to rev up very high. Half choke or full choke I can get it to run for a few seconds at a higher RPM (more or less like it should be) but then is starts to sputter as it should when the choke is pulled. I let off the choke and the rpm raises but soon falls off. The mower has been sitting for a while and it could be the card. I'm running Seafoam in it now to see if clears up. any suggestions


#16

mhavanti

mhavanti

If the seafoam doesn't clear it up and I'd not hold my breath. Be ready to clean the carb. Run wire thru all the circuits to clean them really well. If that doesn't open it up, get back to us.

Max


Footer Links 1

Top