2. Engine
As mentioned previously,
this bike came to me with the engine stuck. As a part of the deal, I
also was given two donor bikes of the same model, but different years.
As 
is often the case, these bikes had been left
outside with the carbs and exhaust pipes removed, so water,
snow and whatever was blowing by had made their way into the engine
cylinders and they were solidly stuck and not looking very good at all
- as per the photo to the left. After letting them soak for
several weeks with a liberal amount of penetrating oil in the barrels,
I pulled them apart to
see what could be saved, Interestingly, both donor engines appear to
have failed due to holed pistons, so naturally I was curious whether
the project GT550 had the same problem. As well, I had been told that
this model of Suzuki had a fragile starter, but when I pulled these
apart both donor bikes showed no sign at all of starter problems. One
of them
even still had its starter motor fitted, and when I'd pulled
it out, I tried it with a power source, and it spun freely.
At the end of the day, I had about one and a half engines with
serviceable bits and pieces suitable as spares - one actually had
a set of first over pistons which are
becoming rare to
find now. The barrels were in rough shape, but at least could possibly
be bored out, and one set of engine side covers were worth
keeping
The next step was to strip down the project bike and see what its
problem was. As it turned out, it had more than one. Once the head was
off I was initially relieved to not see any holes in the pistons,
however the centre cylinder had a lot of small metal particles on the
top of the piston as well as in the exhaust port, and once the barrels
had been pulled off it was clear where they had come from per the
photos below. The centre piston's gudgeon pin had snapped, and then the
piston had essentially self destructed. The bits of broken aluminium
alloy that had fallen down had
lodged between the crank throws and the crankcase which was why it
wouldn't
turn over. As well, when I pulled off the clutch basket, the starter
clutch assembly basically fall apart as the centre boss had come
completely apart. In the photo below to the right, you can see the
broken one to the left, and what it's supposed to look like to the
right.
Suzuki completely redesigned the starter clutch assembly in 1975, the
year after my bike was built and obviously the updated starter clutch
version had
never been installed. The service bulletin is GT-26, dated
August 15, 1975 and a copy can be found here. I have two 'good' old style
starter clutch assemblies from the donor bikes as neither of them had
been updated either, but I wasn't too happy with
using these
as I could reasonably expect the same failure mode again at some point
- and as I was putting this bike on the road for my wife to use, I
doubted she
would be impressed if it quit working !
I am looking to see whether I can track down a new style starter clutch
assembly and we'll see what happens. At the moment, I'm waiting on
parts, seals and gaskets before I start to put the engine back
together.
March 20, 2009
The
new style clutch basket and starter drive assembly has arrived,
together with most of the seals, gaskets and other bits and pieces I
need. I managed to track the starter clutch assembly down in the UK
from Suzuki-Dave
who is a member of the UK Kettle Club, and from whom I've bought other
items previously. Tracking down all the other seals I needed has taken
some time, as some have not been available from Suzuki for quite a
while - for example the oil seal that goes behind the drive
sprocket ( 09283-25050 ) I
finally sourced from a dealer in New Zealand. Most of the crankshaft
bearings and the connecting rods are no longer available from Suzuki
either, so I'm hoping that the crankshaft I have will be OK.
I
spent a very pleasant day up at Fred's earlier this week washing the
engine cases in his parts washer, and they are now look much better. I
also rinsed out the crankshaft assembly just to try and flush any
remaining small bit of aluminium off the big end bearing etc. and that
all looks pretty good as well. As my wife is out of town this week, I
very seriously thought about washing the crankcase halves in our
dishwasher - this has been done by a number of folks and supposedly
works well, however my guess is that they are all single (or divorced)
so in the end I decided that I'd better not push my
luck with SWMBO'd.
As per Suzuki Service Bulletin #GT-26 of
August 15, 1975, the new starter drive assembly ( 21200-34820 ) was
introduced with engine number GT550-63692 and is quite
different from the older style, as can be seen from the photo below -
the new style is on the left with the new starter clutch gear above it.
These assemblies come as matched sets and per the bulletin
must be
replaced as a unit. Of course none of these parts are still
available from Suzuki, so anyone restoring these engines will likely
have to take their chances.
.
With a bit of luck, I should have the engine back in the frame by mid
week.
March 27th, 2009
It
seems luck is in short supply, as I am still waiting for a couple of
seals to arrive. In the meantime, I have assembled most of the engine -
while doing so, I noticed that in addition to revamping the clutch
assembly Suzuki had also changed the gudgeon pin design. The piston
failure in the centre cylinder seems to actually have started with the
gudgeon pin cracking in half, and so I was pleased to see that the new
pins had a much thicker wall, as can be seen in the photo
below.
Presumably then, the failure my engine had was not an isolated event !!
Updated
August 17th, 2010
©
Ian R. Sandy
