Author Topic: Lemans top end refresh - how far do I go ?  (Read 489 times)

Offline Bazil

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Lemans top end refresh - how far do I go ?
« on: June 26, 2021, 07:02:56 PM »
The patient - Mark IV Lemans
Age - 72,000 kms / 35 years
Vital signs - leakdown test about 8 % , compression test 125 / 127 psi , smoky exhaust , fuel consumption awful (and always has been over the last 25,000 kms)
General health -running pretty fine, despite the smoky exhaust !  :copcar:

The Lemans is in need of a top end refresh - it's getting pretty smoky, which I assume is valve guides.

I'm intending to have the valves K-lined. My question is how far do I go ?

Given the compression & leakdown results are  new rings are warranted ?

While the heads are off, is it worth considering a port job, or dual plugging the heads ? How much benefit versus expense are we looking at ? (guzzi content)

Thanks in advance from those more expert than me.

Bazil
1986 Lario ( long gone, still missed)
1985 Mark IV Lemans ( Gina)
1991 V40 Targa ( L'il Jeannie)
1962 Royal Enfield Crusader Sports

Offline moto-uno

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Re: Lemans top end refresh - how far do I go ?
« Reply #1 on: June 26, 2021, 07:47:39 PM »
  If you checked compression with wide open throttle , then your compression is really low .
  Twin plugging , when all was said and done on my Le Mans 2 made it run better at lower rpm's ( never figured on that ) and allowed for a bit
more retarded timing to reduce detonation ( pinking ) .
  Porting ( if they have a flow bench or have done Guzzi heads for racing ) is usually pricey , but sure can wake up a motor with an exhaust system .
  Have someone with a proper bore gauge check your cylinders before hoping rings will be all you need .
Sure there will be more to follow :) . Peter

Offline Scout63

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Re: Lemans top end refresh - how far do I go ?
« Reply #2 on: June 26, 2021, 08:31:54 PM »
I canít get into a top end without doing everything short of porting. Check cylinders, pistons, rings, valve seats, guides, head deck etc.  It just seems like short money once it is apart.
Ben Zehnder
Orleans, MA USA
1971 BMW R75/5
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1978 Yamaha SR500
1979 Moto Guzzi V1000G5 - T3FB mild custom
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Offline John A

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Re: Lemans top end refresh - how far do I go ?
« Reply #3 on: June 26, 2021, 09:33:55 PM »
I think itís best to do rings and valves at the same time because better sealing of the valves puts more pressure on the rings and vice versa.
John
MGNOC L-471
It is easier to fool people than it is to convince them that they have been fooled-Mark Twain

Wildgoose Chase Moto Guzzi

Re: Lemans top end refresh - how far do I go ?
« Reply #3 on: June 26, 2021, 09:33:55 PM »

Offline jacksonracingcomau

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Re: Lemans top end refresh - how far do I go ?
« Reply #4 on: June 27, 2021, 05:52:26 AM »
The patient - Mark IV Lemans
Age - 72,000 kms / 35 years
Vital signs - leakdown test about 8 % , compression test 125 / 127 psi , smoky exhaust , fuel consumption awful (and always has been over the last 25,000 kms)
General health -running pretty fine, despite the smoky exhaust !  :copcar:

The Lemans is in need of a top end refresh - it's getting pretty smoky, which I assume is valve guides.

I'm intending to have the valves K-lined. My question is how far do I go ?

Given the compression & leakdown results are  new rings are warranted ?

While the heads are off, is it worth considering a port job, or dual plugging the heads ? How much benefit versus expense are we looking at ? (guzzi content)

Thanks in advance from those more expert than me.

Bazil
You sir,
Are one lucky chappie
Not many sellers tell you they did that (25kKm is 15 odd k miles), with  awful fuel consumption. Damage is done, but fixable..
Paint stripper is your friend, non caustic, please.
Brakeclean, alcohol ,water
Once all is clean, measure and blueprint to book
Your k liner head man will tell you about valves, guides and springs
RIngs are extremely unlikely to be usable
Followers and gudgeon pins dearer but relevant, only reuse if perfect
Yes there is much more to be had with tuning but to get normal (or better) fuel consumption is the goal to fix yours
Net sometimes misses the bleeding obvious
Symptoms maybe head gasket, guides or rings
Cause might be PO

Online Stevex

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Re: Lemans top end refresh - how far do I go ?
« Reply #5 on: June 27, 2021, 11:00:08 AM »
Those compression test results are really low as already stated.
Have you considered a leak down check to find out exactly where the combustion chambers are leaking?
Steve
1980 Le Mans II
2009 Honda CB1300S
2005 Aprilia Tuono
Chief mechanic to wife's 696 Monster

A 'gnat's cock' is an accurate unit of measurement.

Offline Bazil

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Re: Lemans top end refresh - how far do I go ?
« Reply #6 on: June 27, 2021, 05:11:35 PM »
Stevex - the leakdown showed rings as the culprit - no noise from inlet or exhaust side, just a gentle gasp through the open oil dipstick hole.

Martin - thanks for the comments. I'll make it my mid winter project - gasket set is on order and I'll see what I need from there

cheers
1986 Lario ( long gone, still missed)
1985 Mark IV Lemans ( Gina)
1991 V40 Targa ( L'il Jeannie)
1962 Royal Enfield Crusader Sports

Offline Groover

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Re: Lemans top end refresh - how far do I go ?
« Reply #7 on: June 29, 2021, 07:09:21 AM »
What is the normal/good compression supposed to be on those?
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1987 Moto Guzzi LM1000SE, a
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Offline moto-uno

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Re: Lemans top end refresh - how far do I go ?
« Reply #8 on: June 30, 2021, 07:46:45 PM »
 Not too sure if this is really relevant , but my Le Mans 2 with the stock 10.5 to 1 compression pistons ( and 2 friends with same model )
all ran over 200 psi with full throttle test . At 175 psi or lower they were noticeably softer powered .  Peter

Online Murray

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Re: Lemans top end refresh - how far do I go ?
« Reply #9 on: June 30, 2021, 08:18:20 PM »
Also check the condition of the carb needles with that low compression I would of expected a 1 in front of the kms numbers but as others have said its pretty worn. You'll probably get a lot back from simply restoring compression so isolating gains from a port or twin plugging might be a little marginal. Timing chain and tensioner or a set of steel gears while its apart and you might want to look at the clutch while its easy to see.

Offline Bazil

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Re: Lemans top end refresh - how far do I go ?
« Reply #10 on: June 30, 2021, 08:29:46 PM »
Over 200 psi sounds impressive ! I assume that would be with pods or no air filter. Mine has the stock Mark IV airbox, which might hold things back a bit as well ?. I would have expected 160 to 180 psi if I was guessing.

Timing chain tensioner is a Valtek type and seemed to be doing it's job. Carb needles, seats and slides have about 20,000 k on them I think.

The engine guy is booked up for a month, so I'll tackle it all then, and he will check out valves, springs etc and do the k-line , while I check rings & bore

Thanks everyone
1986 Lario ( long gone, still missed)
1985 Mark IV Lemans ( Gina)
1991 V40 Targa ( L'il Jeannie)
1962 Royal Enfield Crusader Sports


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