Guzzi Bore, Pistons and Cam. Bore.

Took the head and barrels off to inspect the cam followers. Not a happy
sight greeted me.

http://www.sweller.dynalias.org/guzzipistons/

What's caused the scoring, why's the carbon oily and will it polish out?

It fucking better had as the pistons are made of unobtanium. I have a
set of Nikasil bores that are graded the same as the pistons (I know I
have to change the rings). Good idea or not?

What say the panel?

 

"sweller" wrote...

Hi mate,

First thoughts: looking at the l/h piston, shouldn't the ring gaps *not*
line up? That'd account for a lot of the oily carbon, blow-by into the
carnkcase would push oil out of the breather and into the carb, hence
deposits building up... the scoring in the barrel will let some more
combustion gas past, but nothing compared to having the ring gaps lined
up[-1]!
When you took the carbs off, were the intake ports and carb internals
oil-misted?

The cam followers look to me like it's been run dry, is the cam badly
scored? I had a Vauxhall that did this, an oilway wasn't drilled at the
factory, about 1/4 inch was worn off the cam lobe in about 25K miles...
Sounded *very* tappety too.

Looking at the scored barrels, does the cutaway in the base face towards
the centre of the V? if'n it does, it looks like the piston's been rocking
in the bore (a touch undersize?) with sommat hard and gritty picked up by
the piston skirt[0] (possibly the bits of lost case-hardening off the cam
followers?)

The scoring on the l/h piston looks a lot[1] like it's been siezed and left
to cool, then ignored or maybe just had the rings changed (

I'd be checking whether the pistons *can* be reused[2], they look pretty far
gone to me, particularly the left, and the scoring... if the scoring will
clean up with a hone, great, if not you're looking at a rebore and pistons,
or perhaps just the replacement (same size?) barrels and fresh pistons

Whatever you do, it's going to cost, and if it were mine and I cared about
it I'd want to be sure that the bottom end hadn't suffered similarly, plus
make sure the oil pump's in decent order (it's a bugger that they don't fit
gauges, can save an engine if you have one).

IANAM,JAHE, so could be barking up several wrong trees...

--
Dave H.
(The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader

[-1] The ring grooves often have pegs to locate the ends of the rings 120
degrees or so apart
[0] Contrary to common sense, grit and shit often wear the harder material,
as the grains embed in the softer material and wear the harder.
[1] For values of a lot approaching 100%
[2] And whether they're the right size for the bores anyway.

 

Four strokes don't have their rings pegged (in the same way as a two
stroke) and the rings jiggle round quite happily.

Whether they're 120 degrees spaced or not the scoring wasn't caused by
blow by. If it was it's convenient that it's so accurately spaced around
the piston.

 

Exactly what I was thinking. You want 120 degree spacing of the ring
gaps.

 

The rings may have lined up because of my handling of them but I can't be
certain. The evidence of any blow by would be burning on the piston.

No. I suspect the valve guides for the oil as these bikes are very
susceptible to having their crankcase pressurised. Since I changed the
pistons (two years ago) it doesn't suffer from it anymore.

Which is why I'm discounting blow by. Take my word for it, anyone who
followed that machine at full chat a few years ago would have had the
Royal Flying Corp look.

Cam looks ok but that's peering down through the follower hole.

Could be possible.

Piston wasn't scored when it was fitted two years ago, the bike hasn't
seized and I've not changed the rings.

Pistons are - for all intents and purposes - unobtainable. I will see if
I can clean them up.

 

Umm. Having gust replaced a seized Nikasil barrel and piston, that
left-hand piston looks like a seizure (hopefully I'm being overly
pesimistic) and if I've read the pictures right, it's in sort of the
same place that mine seized, i.e. on the diagonal, just beside the
gudgeon pin bores. My theory is that when they overheat the pistons
expand along the line of the gudgeion pin, and the side thrust of the
con-rod on the power stroke shifts the point of maximum pressure onto
the diagonal, *except* that yours has marks on the opposite diagonal
to mine. Ho hum. It sort of looks, in the picture labelled 'Left Hand
Piston (not wanting to labour a point..)', as though alloy is visible
on the rings, but that could be reflections.

The carbon deposits could be oil that's got past the rings. Either
that or you're running rich on that side. That would be odd, though,
'cos you'd expect it to run cooler.

I've also seen pitting on my cam followers, but not as severe.

I'm not certain about this 120 degrees piston ring thing: one book I
read suggested that they can rotate in their grooves at a few RPM,
which would explain why early K100s sometimes smoke heavily when left
on the sidestands: the oil rings can stop with the gaps facing
downwards. Could be bollocks, though.

Will it polish out? 'Maybe' is the answer. My LH cylinder bore was
fucked.

 

Although the scoring looks pretty bad I'd clean it all up and get the
micrometers on the pistons. Check for ovality (specs are in the Good Book).
If the nikasil is in *any* way damaged, bin the barrells. If the pistons are
round rather than oval and polish up ok, get a set of older standard bore
iron liner barrells off a T3 or (Spada if yours are 950cc), and get them
honed to suit your pistons.
The cam followers are a dead give away though: Crap oil. What's the cam
like......? As you seem to like giving the old girl a bit of stick and these
engines do run hot, *only* use fully synthetic 10w50 or 20w50 and change it
every 2500-3000miles. When was the last time you changed the spin on filter
inside the sump? Also as previously suggested, check the oil pump very well
for wear.
Just my tuppenceworth.

JB

 

You've been thrashing it, haven't you?

 

Of course he has. It's what Guzzis are for. Oh Yuss indeedy.

JB

 

It has LM I iron barrels at the moment. I have the old (good) T3 nikasil
barrels it had originally.

I change the oil every 3000 (ish) miles, the filter every third change
(as you know the book says five but even I think that's pushing it).

I use semi-synth SL 15/50. The cam will get closer examination tomorrow.

 

Ah ok. I was confused there. First off, I think a good intensive measuring
session is in order, both pistons _and_ barrells. Don't piss about with
vernier calipers for the pistons, use proper micrometers. The bores will
need proper bore guages and a micrometer to suit. As these are not cheap or
daily use tools for mere mortals, find a good old fashioned general
engineers, a toolmaker or a reboring firm who might make these measurments
for you for beer or hire you the tools (don't hold your breath on the last).
Colleges are also good for these things.
Only when you've got the correct measuerments can you make a diagnosis and
see what is salvegable.

Agree fully with the above and follow the same intervals/procedures.
(although personally I only use the fully synth stuff).
I would now be seriously looking at the oil pump and pressure relief vavle
in the sump.

JB

 

I only mention it in the spirit of referring to his post of last year,
around this time[1], when he was asking for advice because his front tyre
was ripped to shit right round to the beading. He's just showing off.

[1]http://groups.google.co.uk/group/uk...6?lnk=gst&q=yhcmslatiadss&rnum=2&hl=en&fwc=1#

 

Sir sir sir pla with us sir. Sir pla with us...

 

The oil usually found in your wheel rim might have been more use in
the engine.

Now the jokes are over I can be serious.

I don't know what Nikasil really is iyswim. It's a 'trade' name but
is it a chrome substitute, is it a powder coating, is it a flame
coating with a high percentage of chromium or what? If anyone can find
out then I've probably got a contact who can get the barrels ground
out to clean, re-coated and then finish ground to size.

Obviously the company doing the work would want some cash and even
more obviously I'd have to sneak it in through a third party because
there was a bit of bad feeling when I decided I'd have more fun
working for a competitor than them.

 

It's electrodeposited oleophilic nickel matrix silicium carbide,
apparently.

 

There are several places that do just that, and advertise in the comic.

 

This is why I'm confident it's not the rings as I corrected its Sopwith
Camel tendencies.

The problem is with the iron bores it has at the moment. I have a set of
good nikasil bores (some form of chrome plating) which if the pistons are
recoverable I will see if they can be matched.

I will be visiting my local engine re-conditioners and asking they're
advice - he's already going to be doing some head work for me.

 

I've no objection to him having a good hiding now and then.

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, JB

I can supply bore gauges and micrometers.

--
Wicked Uncle Nigel - "He's hopeless, but he's honest"

WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
SBS#39 OMF#6 Enfield 500 Curry House Racer "The Basmati Rice Burner",
Honda GL1000K2 (Fallen apart) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
Suzuki TS250 "The Africa Single" Honda ST1100 wiv trailer Norton 850 Commando
Kawasaki GTR1400

 

The piston, it may have been running hot on one pot for some reason, or
an oil jet is blocked and not spraying oil onto the bore (if fitted.
Don't you have to be careful about not using high sulfur petrol with
Nikasil?

As for the follower, looks like it's not been spinning for some reason,
they have to spin to work properly. Could have been not getting enough
oil maybe? It's rather blue looking, which means overheating.