B man
Tecumseh FTW!
oh. heres a thought. have you checked the lobes on the cam shaft?
My project and my woes :-(
- Thread starter Aazza
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B man
Tecumseh FTW!
To see if the lobes are worn down
Okay, I've been working on this engine again today and I've found some issues.
Basically this engine has definitely been worked on previously and by an idiot at that. I found a bolt rolling about in the oil at the bottom of the engine. I managed to get that out after a lot of sodding about.
I cut a new gasket for the cylinder. I ended up ordering all the gaskets from the post above. I used an oil resistant gasket that's good for up to 120 degs C. It was the closest looking gasket to the gasket already on the engine.
As I started putting everything back together, I noticed I'd lost a bolt. It was was a long bolt that connected the bottom to the cylinder and the cylinder to the cylinder head. Luckily I made a video of me taking the engine apart, because I thought I might forget what bolts went where etc. I watched the video back and the bolt was never removed, meaning it was never there. I remember that the gasket I replaced was shot to bits around this missing bolt hole. So I guess it'd be fair to say the seal was good for nothing around this bolt.
As I continued to put the rest back together, practically every bolt or nut threaded as I torqued them up. So I guess everything had been over tightened previously. Luckily it was the bolts or nuts threading and not the engine threads. So I've cleaned all the threads and replaced the various nuts and bolts.
All I've got to do is adjust the valve clearance, fill it with oil and fresh petrol and I'm ready to kick it over. fingers crossed.......
Basically this engine has definitely been worked on previously and by an idiot at that. I found a bolt rolling about in the oil at the bottom of the engine. I managed to get that out after a lot of sodding about.
I cut a new gasket for the cylinder. I ended up ordering all the gaskets from the post above. I used an oil resistant gasket that's good for up to 120 degs C. It was the closest looking gasket to the gasket already on the engine.
As I started putting everything back together, I noticed I'd lost a bolt. It was was a long bolt that connected the bottom to the cylinder and the cylinder to the cylinder head. Luckily I made a video of me taking the engine apart, because I thought I might forget what bolts went where etc. I watched the video back and the bolt was never removed, meaning it was never there. I remember that the gasket I replaced was shot to bits around this missing bolt hole. So I guess it'd be fair to say the seal was good for nothing around this bolt.
As I continued to put the rest back together, practically every bolt or nut threaded as I torqued them up. So I guess everything had been over tightened previously. Luckily it was the bolts or nuts threading and not the engine threads. So I've cleaned all the threads and replaced the various nuts and bolts.
All I've got to do is adjust the valve clearance, fill it with oil and fresh petrol and I'm ready to kick it over. fingers crossed.......
Just got everything back together, filled with oil and done a compression test - Only a slight improvement.
So I did the air compressor test. I only used about 20psi, but that was plenty. After managing to lock off the flywheel I could actually feel air coming out of the air filter. I could also just about feel air coming from the exhaust port.
So I guess I'm at the stage now, if I can't find some rings I may as well give up on this engine.
I'm going to lap the valves again. I was worried about lapping them back too much, but what have I got to loose now?! I'll give that a go, see if I can improve compression that way. If not, in the bin I guess!!
Oh just a quick question - Is the engine supposed to be at TDC on the compression stroke when the air test is done?? This is what I assumed and is how I performed the test. Thought I'd make sure though.
Cheers
Az
So I did the air compressor test. I only used about 20psi, but that was plenty. After managing to lock off the flywheel I could actually feel air coming out of the air filter. I could also just about feel air coming from the exhaust port.
So I guess I'm at the stage now, if I can't find some rings I may as well give up on this engine.
I'm going to lap the valves again. I was worried about lapping them back too much, but what have I got to loose now?! I'll give that a go, see if I can improve compression that way. If not, in the bin I guess!!
Oh just a quick question - Is the engine supposed to be at TDC on the compression stroke when the air test is done?? This is what I assumed and is how I performed the test. Thought I'd make sure though.
Cheers
Az
B man
Tecumseh FTW!
has it ever occurred this engine my have a compression release?
OzFab
Well-known member
It's extremely possible the engine was 360* out when you did the test so both valves would've been open.
The compressed air will want to push the piston down anyway but, it should end up at BDC at the beginning of the compression stroke. At that point, the inlet valve may still be open slightly so, if you can lock the engine at TDC, you will get a true reading
One thing I figured out while setting the timing on my buggy was that there are two times the piston is at tdc. Compression and exhaust I believe. I set my timing by the holes in the sprocket on the cam and the marks on the crank, would turn over but not fire. Let the timing chain loose, turned the crank all the way around to the next stroke, set the timing there, and it fired right up.
Bman - How would I check to see if it has compression release?
Fabroman - I tried the test 360 degs out on the first test. I then spun the flywheel 360 degs and performed the test again. Still I wasn't sure I was on the compression stroke, so I took the cam cover off to make sure. My manual states TDC is when the cam lobes face down. This was where I locked the crank and performed the test.
Brock3 - I was under the impression that on a cdi engine you get spark at both compression and exhaust stroke, so it doesn't matter which rotation the engine is set to as long as the cam marks are matched up with the piston TDC. One thing is for sure though it certainly wouldn't hurt to try. I'm still trying to get compression up at the moment though, I've not even tried a start up since having the engine back together.
Today I'm going to really lap the valves back. I definitely seem to be losing compression through the valves as apposed to the piston. After reading back through this thread I realised I would also be able to feel air from the oil filler if it were the piston. So fingers crossed I might be getting somewhere.
Cheers
Az
Fabroman - I tried the test 360 degs out on the first test. I then spun the flywheel 360 degs and performed the test again. Still I wasn't sure I was on the compression stroke, so I took the cam cover off to make sure. My manual states TDC is when the cam lobes face down. This was where I locked the crank and performed the test.
Brock3 - I was under the impression that on a cdi engine you get spark at both compression and exhaust stroke, so it doesn't matter which rotation the engine is set to as long as the cam marks are matched up with the piston TDC. One thing is for sure though it certainly wouldn't hurt to try. I'm still trying to get compression up at the moment though, I've not even tried a start up since having the engine back together.
Today I'm going to really lap the valves back. I definitely seem to be losing compression through the valves as apposed to the piston. After reading back through this thread I realised I would also be able to feel air from the oil filler if it were the piston. So fingers crossed I might be getting somewhere.
Cheers
Az
OzFab
Well-known member
Not being sure what stroke you were on implies you got the same result both times, correct?
To be more specific, the valves should be closed so, if the lifters/rockers are above the cam then, yes, the lobes face down. If the rockers are below the cam (albeit, not a very common design) then the lobes should face up
No the result was not the same. First test was done on exhaust stroke and air easily flowed. Second test, I took the cam cover off and checked the lobes were down when first test was done, they were in the up position. So I rotated 360° made sure the lobes faced down and I was indeed on compression stroke. In this position the springs force the valve closed and and the rocker is putting no pressure on the lobes.
Anyway since then I have really lapped the valves back. Now with the air compressor test I feel no air coming from anywhere. I went up to 50psi and still nothing. I actually wasn't able to keep my air gun over the plug hole, it forced me off and caused air to escape. I tried a compression test but found my tester to have a really nasty leak, so I gave up with that.
I've added fuel and tried to start it, no joy.
Tried starter fuel in the plug hole, no joy.
Time for a new engine I think.
:'(
Az
B man
Tecumseh FTW!
you know that could be the problem. your engine is at TDC twice. so maybe you have it on the wrong TDC?
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