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PostPosted: Thu Feb 15, 2018 6:09 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
my cylinder is back. OEM piston, rings, and wrist pin. had to go with a Wiseco wrist pin bearing. they didn't have a OEM replacement.

assembly, leak down test and break-in this weekend.


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PostPosted: Sat Feb 17, 2018 5:34 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
got her running. 1st heat cycle. need to install guards, fan shrouds and seat. couple more heat cycles. then it's time to piss off the neighbors running up and down the block. :)


https://youtu.be/jPp7FKidUz8


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PostPosted: Sat Feb 17, 2018 6:20 pm 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7698
Location: Hope, B.C Canada
Awesome.
Sounds a bit fat at idle but that may be because it was still cold.
Also noticed that it looked like it had a ProX rod in it and that tells me it has been previously blown up.
Just curious but:
1) what is compression ??
2) what were the leak down results ??
3) fuel flow rate result ??
4) what fuel you running ?? (That other piston did look ok though)


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PostPosted: Sat Feb 17, 2018 7:31 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
It maybe running a little fat but I would rather it be a little fat for break-in. plug doesn't look fat. running stock jets at sea level with Uni filter.
I believe it has a stock OEM rod.
leak down passed. six lb's for six minutes with no leak down.
Fuel flow rate was 4oz at approximately 10 seconds. I will check again now that all the bubble are out the the fuel line.
It had very poor fuel rate before due to the left side crank seal being shot and old pulse line.
I am running pump fuel at 91 octane at a oil ratio of 32-1 of caster maximum 927
I haven't checked the compression but will do that tomorrow when it's cold. curious myself.


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PostPosted: Mon Feb 19, 2018 12:28 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
my cold compression is only at 130. now I am concerned. leak down test passed with no leakage. 6 lb's for six minutes.
just touch the starter and it fire's up and idles fine. went through two heat cycles and a run down the block just cruising after warming it up.
using cometic base and head gasket.
should I have higher compression or has the rings just not seated? if it didn't run so good I would be really concerned. should I be concerned??
thoughts?? suggestions?


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PostPosted: Mon Feb 19, 2018 1:29 pm 
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Joined: Sat Nov 08, 2014 7:40 am
Posts: 916
Location: Tallahassee Florida
It will go up as the rings seat.
I would not be concerned at this point.


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PostPosted: Mon Feb 19, 2018 3:33 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
Thanks FloridaEdd
That puts my mind at easy for now. I took my time assembling and know its assemble to spec's. it's hard to trust people to do a good job.


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PostPosted: Mon Feb 19, 2018 5:55 pm 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7698
Location: Hope, B.C Canada
roadx wrote:
my cold compression is only at 130. now I am concerned. leak down test passed with no leakage. 6 lb's for six minutes.
just touch the starter and it fire's up and idles fine. went through two heat cycles and a run down the block just cruising after warming it up.
using cometic base and head gasket.
should I have higher compression or has the rings just not seated? if it didn't run so good I would be really concerned. should I be concerned??
thoughts?? suggestions?


None of the engines I have ever rebuilt have ever come up any measurable amount. If it tested 130 it generally stayed there.
You are testing with the throttle wide open right ??
Your tester is accurate right ??
We have seen many a tester that is out of calibration on this site.
On a positive note I have to say that many are really hung up on compression. High compression is good for low end torque and that's it as far as I am concerned. I have run engines on my oddy with 110 and it ran fine. You wouldn't feel the FN difference between 130 and 150 anyways. I am not sure but I think the pilot should be around 145. Someone correct me on this if I am wrong. At the end of the day this machine will run fine and run for years.
Just my opinions.


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PostPosted: Tue Feb 20, 2018 12:43 am 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
Thanks canadian oddy
yes, the throttle was wide open.
my compression gauge is a Bosch gauge but I have never tested against another gauge.
I will stop stressing and just keep my eye on it and run it.
After I get a few hours on it I will report back weather it has changed or not for you curious folk.


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PostPosted: Tue Feb 20, 2018 12:50 am 
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Joined: Tue Jan 17, 2012 3:19 am
Posts: 7698
Location: Hope, B.C Canada
Just for your own piece of mind test that gauge.
Check it against the pressure gauge on your compressor. I have run across this issue myself. My Chinese gauge was out (low) by ten pounds. My USA gauge was the same as my compressor pressure.
At the end of the day this thing will run for years.


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PostPosted: Tue Feb 20, 2018 12:57 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
I will check the gauge against my brothers gauge next week when I can get out and break it in on his land. I would check against my air compressor but I know it's off.


canadian oddy wrote:
Just for your own piece of mind test that gauge.
Check it against the pressure gauge on your compressor. I have run across this issue myself. My Chinese gauge was out (low) by ten pounds. My USA gauge was the same as my compressor pressure.
At the end of the day this thing will run for years.


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PostPosted: Tue Mar 27, 2018 9:31 pm 
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Joined: Fri Jul 04, 2014 7:33 am
Posts: 1070
No-one mentioned this but, your old piston was telling a very LEAN story. Research piston wash (You had very little) and also the underneath part of the piston crown just above the wrist pin is BLACK. It should not be that black. Black in the area of the piston bottom indicates over-heat and some pre-ignition. Get enough heat, and its BOOM - BELOW the combustion chamber. Here-in was why you were back-firing originally. - Lean condition caused by leaking crank seal and low fuel flow all contributed to this effect, and a hot piston bottom caused some explosions within the crank case.

As for your new Engine concerns of compression being low, could be several things. What clearance and ring end-gap did you 'hone' your cylinder for? Clearance figures should be minimal on a new Engine. Who honed the cylinder, and with what kind of hone tool, plus clearance of these parts makes a big difference. All around how tight the clearances are, how perfectly round the hone job was, etc. Break-in should not raise your compression more than 5% (So, 7 psi) IF at all.

Dynamic CR (Compression ratio) is taken from the top of the exhaust port to the head, measured in mm, and then volume of the combustion chamber which is volume of the cylinder head minus volume of the piston crown (Volume of a cone) PLUS the volume of the piston blew the top of the cylinder and squish... complicated..... There are online calculators for getting your CR right. It doesn't look like if from the picture, but if anyone ever ported or shaved the TOP of the exhaust port then you can expect lower compression but potentially better top-end when compression is raised back up with modified combustion chamber volume (CR). Also if you used a THICKER base gasket then you've also raised your exhaust port and changed your combustion chamber volume.

Head gasket thickness, base gasket thickness, and squish band also take, make, or break your compression figures. Your squish band should be no tighter than 55 thousandth. I've read some FL350 run loose at like 90 thousandths (LOL). The larger you go, the less CR and PSI you'll have.


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PostPosted: Wed Apr 04, 2018 12:19 pm 
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Joined: Wed Jan 17, 2018 3:34 pm
Posts: 81
Location: San Diego Ca
thanks for the info. yes, it was running very lean due to the crank seal on the clutch side was leaking.
the Engine was bored with an OEM two over piston and rings. the shop that did the bore had parts on hand and only does atv/ two stroke motorcycles and utv's and he was familiar with pilots so I assumed they knew what they were doing.
it was installed with cometic gasket set. I think the low compression is from the head gasket being too thick.
I am just going to run it. get it good and broke in. then maybe pull head and check thickness and squish. it runs good. just tap the starter and it fires but still a little on the rich side in the higher rmp's with a 138 main on first clip. going to a 135 on third clip and see how it goes. jetting is real close using 91 pump gas at 32:1. by the way running at sea level with Uni filter and stock airbox.


ZeroClient wrote:
No-one mentioned this but, your old piston was telling a very LEAN story. Research piston wash (You had very little) and also the underneath part of the piston crown just above the wrist pin is BLACK. It should not be that black. Black in the area of the piston bottom indicates over-heat and some pre-ignition. Get enough heat, and its BOOM - BELOW the combustion chamber. Here-in was why you were back-firing originally. - Lean condition caused by leaking crank seal and low fuel flow all contributed to this effect, and a hot piston bottom caused some explosions within the crank case.

As for your new Engine concerns of compression being low, could be several things. What clearance and ring end-gap did you 'hone' your cylinder for? Clearance figures should be minimal on a new Engine. Who honed the cylinder, and with what kind of hone tool, plus clearance of these parts makes a big difference. All around how tight the clearances are, how perfectly round the hone job was, etc. Break-in should not raise your compression more than 5% (So, 7 psi) IF at all.

Dynamic CR (Compression ratio) is taken from the top of the exhaust port to the head, measured in mm, and then volume of the combustion chamber which is volume of the cylinder head minus volume of the piston crown (Volume of a cone) PLUS the volume of the piston blew the top of the cylinder and squish... complicated..... There are online calculators for getting your CR right. It doesn't look like if from the picture, but if anyone ever ported or shaved the TOP of the exhaust port then you can expect lower compression but potentially better top-end when compression is raised back up with modified combustion chamber volume (CR). Also if you used a THICKER base gasket then you've also raised your exhaust port and changed your combustion chamber volume.

Head gasket thickness, base gasket thickness, and squish band also take, make, or break your compression figures. Your squish band should be no tighter than 55 thousandth. I've read some FL350 run loose at like 90 thousandths (LOL). The larger you go, the less CR and PSI you'll have.


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