Wildgoose Chase Moto Guzzi

General Category => General Discussion => Topic started by: Bazil on June 26, 2021, 07:02:56 PM

Title: Lemans top end refresh - how far do I go ?
Post by: Bazil 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
Title: Re: Lemans top end refresh - how far do I go ?
Post by: moto-uno 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
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Scout63 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.
Title: Re: Lemans top end refresh - how far do I go ?
Post by: John A 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.
Title: Re: Lemans top end refresh - how far do I go ?
Post by: jacksonracingcomau 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
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Stevex 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?
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Bazil 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
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Groover on June 29, 2021, 07:09:21 AM
What is the normal/good compression supposed to be on those?
Title: Re: Lemans top end refresh - how far do I go ?
Post by: moto-uno 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
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Murray 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.
Title: Re: Lemans top end refresh - how far do I go ?
Post by: Bazil 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