| Author |
Message |
    
ross perrin
New member
Username: Eye12wall
Post Number: 1
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 19, 2010 - 09:34 pm: | 
|
i have a 98 bigfoot w/18 briggs w/65 hrs. ,the other day i was out on the lake going to move and it started blowing oil out the breather in the air cleaner with a loss of power.had to get towed in,any ideas? |
Erich Kelter
Advanced Member
Username: Fisherman
Post Number: 144
Registered: 11-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 20, 2010 - 07:08 am: |
|
Well it could be a stuck exhaust valve, rings really shot, hole in piston. Best to do a quick compression test and get the numbers and post them. |
ross perrin
New member
Username: Eye12wall
Post Number: 2
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 25, 2010 - 09:09 pm: |
|
did a compression check, 60 on one cylinder 38-40 on the other. pulled apart, checked rings,valves, springs, oil rings end gap were slightly over tolerance .040 but not wore excessivly or broke like expected.compression rings good.cleaned all valves, not really dirty, pretty clean all thru. not many hrs. like i said. still puzzled, |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 410
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 26, 2010 - 08:11 am: |
|
Did you look at the breather assy that sits on the block, with the vent tube to the carb. It has a one way valve.. see if it's intact. It also has a couple of small drain back holes, see if they are open. The assy is somewhat of an oil separator also.
When you re assy the engine, you can use a fine ball hone, or even just a scotch brite pad. Just a little de glaze.. doesn't need much.
Compression readings are low.. rings not stuck in grooves?.. |
ross perrin
New member
Username: Eye12wall
Post Number: 3
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 26, 2010 - 08:19 pm: |
|
i put a new breather on upon reassembly, with new gaskets everwhere,nothing changed, still low readings on the one piston.thats what i thought since it was running fine before this happened so i wouldnt think wore valves or rings wouldve been it since it was all of a sudden. but i checked the rings anyway. all thats left is valves and seats i guess.i ordered new rings to put in and well go from there? |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 411
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 26, 2010 - 08:41 pm: |
|
you could do a leak down test, air pressure in the plug hole.
valve lash is .005 with piston down the bore a 1/4" after TDC of compression stroke.. to get it off the compression release.
rings are the only thing I can think of that would be both low compression and blow by. Like you say it's a mystery at this point.
Unless head gasket leaking into the pushrod area. Usually not an issue on the vanguard. You using the thick composition graphite gaskets? |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 412
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 27, 2010 - 09:09 am: |
|
You know what we forgot.. the compression release. That's why you got 40-60.  |
ross perrin
New member
Username: Eye12wall
Post Number: 4
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 27, 2010 - 10:37 pm: |
|
what do you mean by the compression release? |
Erich Kelter
Advanced Member
Username: Fisherman
Post Number: 147
Registered: 11-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 28, 2010 - 08:32 am: |
|
I'm almost wondering if Roger might have it, head gasket with a piece burned through. We had an old campground mower that still ran with about 3/16" piece of head gasket completely gone, wouldn't idle very well, but ran okay at speed. |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 413
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 28, 2010 - 11:44 am: |
|
Ross, the vanguard camshaft has a "cam within the cam" that at cranking speeds pushes a steel ball outward through a hole in the heel of the intake lobe, pushing the cam follower and valve off it's seat, releasing some of the compression. This allows any half charged lawn&garden battery or a kids arm on the pull rope to start the engine.
As for the oil in the air cleaner issue, it's important to have a good piston fit and ring seal, but other than that, there's a lot of crankcase venting issues that cause the problem you had. Like you said, since it started all at once you didn't expect it to be worn rings, etc.
Some of the causes I've seen are:
vehicle gets tilted far to the flywheel side, the crankcase throws more oil up underneath that breather than it can handle, and it instantly soaks the oil filter and carb throat, making a smoke screen out the tailpipe. I've heard guys make several left hand doughnuts and have the problem, etc.
over full on the dipstick can aggravate the problem
the crankcase has to be sealed other than the vent tube. I've heard a bad dipstick seal can cause the problem. that can also cause the fuel pump to not work well.
Since both pistons are more or less going up and down at the same time, there's a lot of sucking and blowing, wheezing, pressure differential in the crankcase as compared to a normal auto engine, this is why things are so delicate for good operation.
I vent my breather through a hose to a remote canister with a filter.. got tired of trashing air filters. If you do this, be sure to seal up the hole in the air filter base where the original hose came through.
The head gasket issue I mentioned is more common on some single cylinder briggs. |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 414
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 28, 2010 - 11:49 am: |
|
The valve lash adjustment is very critical, the part about being a 1/4" down the bore, to get off the compression release ball. Excessive intake valve clearance negates the compression release and can cause hard cranking. This might be the difference you are getting, the 40-60 compression reading. |
ross perrin
New member
Username: Eye12wall
Post Number: 5
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 28, 2010 - 03:22 pm: |
|
i did a leak down test upon reassembly, i know,i shouldve done that to start with, anyhow. now the leak down test with new gaskets and breather, i have some leakage coming out the intake side on both pistons. this indicates trouble with the intake valves or seats right? would lapping the intakes be enough? |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 415
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 28, 2010 - 11:29 pm: |
|
You had the rocker arms backed off and it was blowing out the intake ports? Or you just put air to the cylinder and let the piston go to the bottom? Like you said, it's hard to imagine anything wrong with 65 hours. |
ross perrin
New member
Username: Eye12wall
Post Number: 6
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 30, 2010 - 06:39 pm: |
|
i had valves set,piston at tdc, put 25psi to cylinder and had some leakage out intakes. took heads off, lapped valves very slightly and reassembled, now no leakage. putting back together to run, we'll see then,thanks guys |
Erich Kelter
Advanced Member
Username: Fisherman
Post Number: 148
Registered: 11-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 30, 2010 - 08:41 pm: |
|
I can just see Ross laying strips in the grass now... |
Rogersmith
Advanced Member
Username: Rogersmith
Post Number: 416
Registered: 01-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 30, 2010 - 11:12 pm: |
|
I wonder if my point about valve adjustment and the compression release was missed. If the valves are set right, the intake valves will not be fully seated at TDC due to the compression release, they will be off their seats a few thousandths, and you would see leakage if a leak down check was done at TDC.
The factory procedure is to rotate past TDC until the piston has dropped a 1/4" down the bore(take out the spark plugs and stick a pencil, etc in the cylinder. Set both valves at .005 right there. |
ross perrin
New member
Username: Eye12wall
Post Number: 7
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 31, 2010 - 10:10 pm: |
|
i did get your point about the comp.release.i did do this,forgot to mention that. motors back in ,just need to get govenor and linkage set properly but sounds good otherwise,thanks for the info.eye12wall |
Shop Talk: Tech Tips and Q&A section