Author Topic: 700 miles on rebuilt lemans engine and possible oil issue  (Read 163 times)

Online amamet

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rebuilt the engine on my 77 lemans approx 700 miles ago. gilardoni cylinders and heads redone.  been noticing the plug on the right has been a bit darker and rich.  im using individual choke levers as opposed to the singular cable and lever style.  runs good, hard to start occasionally from what I assumed is the rich plug, left is a nice brown color.

what's really concerning me is when I look through the spark plug hole and the left is dry and still appears dull grey metal but the right one has a bunch of dark build up on it and appears slightly oily and shiny.  rubbed a tip on it and came out a little oily.

just wondering what I need to do at this point? take heads off and examine pistons unobstuctred? I have an auto zone compression tester I can use incase of bad ring run in
thanks and all help is appreciated
Allen

Offline Old Jock

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #1 on: Today at 01:57:18 PM »
I would run a leak down test to see what results I got from both sides.

If that's not possible perhaps a compression test "might" show something

Got one of these remote visual inspection testers to get a better look at the piston?

I wouldn't tear into it just yet.

Have the carbs and fuel enrichers (choke) been overhauled?

Could be on of them is stuck or running rich and that's the problem

I'm not mechanic but had something similar on a Sport that was ring gap stupidity (2 ring gaps lined up perfectly) coupled with a cylinder bore outta spec.

In that case I was getting oil leaks on the bottom end due to presurization and small amounts of oil the throttle bodies.

I've also seen stuck "chokes" I think the carbs enrich the fuel rather than choke the airflow

Wiser heads should be along soon

Online amamet

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #2 on: Today at 02:25:29 PM »
carbs are rebuilt, chokes are fully seated. plug threads have a slight sheen to them, a little oil maybe.  its the top of the pistons that are bothering me.  hard to see anything through plug hole but what I do see is a little build up and a possibly shiny, wet surface whereas the left is dry and dull grey metal

Offline czakky82

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #3 on: Today at 02:30:14 PM »
Accelerator pumps?

Have the carbs been balanced?

Does it have an airbox? Oil in airbox could show worn/issues with rings.

Do you engine brake hard?


Wildgoose Chase Moto Guzzi

Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #3 on: Today at 02:30:14 PM »

Online dxhall

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #4 on: Today at 03:29:53 PM »
How did you balance the carbs?

I start by measuring the gap at the bottom of the slide with the butt end of drill bits.

After setting the slides equally with the drill bits, I check balance with a gauge - I use a Harmonizer, but there are lots of others out there.  If the gauge shows imbalance, with the slides set equally, something is wrong.  Most common causes of imbalance are air leaks in the rubber manifold (I once bought a bike with one of the manifolds installed backwards) or poor seating of the valves.  There are obviously other (and more serious) causes of imbalance.

Good luck.  I wouldn’t take it apart without further testing.

Online amamet

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #5 on: Today at 03:40:52 PM »
carbs are balanced also with a harmonizer. Runs great. Just curious, how would carb issues lend to a slightly oily, built up  piston top on one side only?

Offline guzzisteve

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #6 on: Today at 04:25:38 PM »
One side is seating the rings & one side not yet. I'd keep riding it, using Dino oil not syn. See how it goes. Go to 1500mi and look. There is a difference between carbs & oil seepage. Doesn't sound like fuel.
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Online amamet

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #7 on: Today at 04:35:57 PM »
rings not seating was what I was thinking. what do I do about the plug getting fouled though?  im using maxima 4 racing oil 20/50 Dino

Online moto-uno

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #8 on: Today at 04:56:02 PM »
  Shiny dark deposits are usually an oil issue . Without seeing the assembly process , I'm curious
if there's a ring alignment concern or possibly a leak in the head gasket from the oil return hole
into the cylinder ? If it doesn't improve soon , it's a quick head removal and maybe barrels .
Good luck , Peter
Forgot to mention , have you re-torqued the heads yet , that's plenty of mileage since assembly . I've
usually done mine the second time by that mileage .
« Last Edit: Today at 04:57:54 PM by moto-uno »

Online amamet

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #9 on: Today at 06:13:44 PM »
Retorqued twice. Once at 500 second 50 miles ago. I’ll get new plugs and run it for a while and see what happens. If it persists, how is it alleviated?

Online lucky phil

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #10 on: Today at 07:17:45 PM »
rebuilt the engine on my 77 lemans approx 700 miles ago. gilardoni cylinders and heads redone.  been noticing the plug on the right has been a bit darker and rich.  im using individual choke levers as opposed to the singular cable and lever style.  runs good, hard to start occasionally from what I assumed is the rich plug, left is a nice brown color.

what's really concerning me is when I look through the spark plug hole and the left is dry and still appears dull grey metal but the right one has a bunch of dark build up on it and appears slightly oily and shiny.  rubbed a tip on it and came out a little oily.

just wondering what I need to do at this point? take heads off and examine pistons unobstuctred? I have an auto zone compression tester I can use incase of bad ring run in
thanks and all help is appreciated
Allen

Sounds like worrying about nothing to me. A rich mixture will also promote an "oily" look simply because incomplete or poor burning results in excess fuel and some cylinder wash. If it doesn't blow oil smoke on the over run from say 5000 rpm or on WOT and the oil consumption is within reason then forget about it and just ride it. If it does it could just as likely be oil through the guide. There needs to be something wildly wrong with an road engine for any meaningful data to be had from "looking at the plugs" There's a reason racers back in the day used to do "plug chops" at the end of the straight at WOT then push back to the pits, because any running at all after the "chop" made the plug reading a waste of time. Everyone still looks at a road engine and "reads the plugs" though expecting low speed running, running on the choke, idling at traffic lights to provide something meaningful in the way of information.   

Phil 
« Last Edit: Today at 07:22:28 PM by lucky phil »
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Online lucky phil

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #11 on: Today at 07:21:01 PM »
  Shiny dark deposits are usually an oil issue . Without seeing the assembly process , I'm curious
if there's a ring alignment concern or possibly a leak in the head gasket from the oil return hole
into the cylinder ? If it doesn't improve soon , it's a quick head removal and maybe barrels .
Good luck , Peter
Forgot to mention , have you re-torqued the heads yet , that's plenty of mileage since assembly . I've
usually done mine the second time by that mileage .

If you mean "ring gap alignment" then no. Rings rotate on the piston during running anyway so sometimes the gaps will align just like the stars.

Phil
If you're not living on the edge you're taking up to much room.

Online amamet

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Re: 700 miles on rebuilt lemans engine and possible oil issue
« Reply #12 on: Today at 08:09:33 PM »
Well this is my first complete rebuild, so yes, I may be worrying too much. I’ve never built an engine before so I’m always “worrying” if I didn’t do something correctly, as in just realizing I never checked the ring gap on the new gilardonis.  I assumed since new I didn’t need to. They may be fine but i should have checked.  But, dry clean piston top with a dry good plug on one side and a slightly oily piston top with a fouled plug leads me to believe the rings in the right didn’t bed in yet or properly.

 


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