GT550 barrels

[Alan H]

Just been looking on eblob (as you do) and noticed that there is a considerable difference in the barrels on the 550s, 'Normally' the base studs are at the same level, i.e. the base flange is the same thickness all the way round, but on some, the rear studs must be much longer as the flange is three fins higher at the back. Anyone know the history of this? Would these be the nickosil barrels and I wonder why they needed to change the design so much for (perhaps) the last year or so?

THIS ONE (clicky link) has the thicker flange type and
THIS K MODEL(clicky again) has the thinner flange type.

However THIS alleged K barrel (clicky) has the thicker flange, so I guess it's not a K, but perhaps a M?

The thick plottens.
Just curious is all, I know a bit about the early models, but not so much on the later ones so if anyone knows the differences between the two barrel types, please post.

[Alan H]

Hmm, having just managed to kick the brain cell into life and look in the parts catalogues, I see that the barrels are the same on the J/K models, but are different to both the L and M models - my catalogues only go to M, so I dunno if they are different after that.
J/K LH barrel 11220-34002
L LH barrel 11220-34100
M LH barrel 11220-34600
the pics don't show the barrel bases though.

[yeadon_m]

Alan, I'm pretty sure the high rear stud barrels mean Nikasil and therefore Ex-USA bikes only - higher power lower torque engines. I have just brought two such bikes and await delivery. I turned down US imports. Lord knows what I've got myself into :-)
Where are you and where in your 550 history? If you are restoring we can help each other, plus there are others on the clinick who have done so. I've done a GT380 so aside from rare bearings, odd bore finishes and unobtainable parts, it should be a breeze :-))
Cheers, Mike

[Alan H]

South Yorks near Barnsley Mike, t'other end of the country to you.
I have a J, a K and a M in the garage!
The K and M are complete but need lots of TLC - LOTS of TLC!
The J is a rolling chassis and a lot of boxes, plus that's the one I want to do as it will be 'the same' as the one I bought in 1972 as a 21st birthday pressy to myself.
I had the original one in bits and seriously tweaked with ports and head worked on (by me) and I've worked on 2 strokes for many years so I know my way around them (currently playing with a 1,7litre V4 2 stroke Yamaha outboard on the dive club boat as well.)
I've managed to accumulate quite a few 550 bits as well, so 'all' it will take now is a quick stripdown & rebuild for each one. Ha!

[Russell]

Hi,

J & k have steel liners and because of the shape of the cast ram air shroud, the fins on the barrels extend out rewards.

L,M have steel liners and have the short fins on the rear of the barrel for the redesigned ram air cover & the casting

Uk & Europe A & B have Nikasil liners and have the short fins on the rear of the barrel for the redesigned ram air cover & the casting is thicker at the back for the longer studs.

USA A & B model's never had nikasil liners but do have short fins and the rear of the barrel is the same thickness as the front.

[Russell]

I got this from the web a few years back hope this explains all.....

This article is my attempt to throw some light on one of Suzuki’s more obscure motorcycles. Even though total production of the 550 exceeded 60,000 examples spread over a six model year (MY) production run, this total was exceeded by both of its three cylinder GT series brothers. Suzuki produced over 80,000 units of the GT750 and over 100, 000 units of the GT380. All three models were originally offered for sale with the beginning of the 1972 MY with the 550 christened "Indy" for the North American market. Apparently, production of the 550 was delayed for some reason because it was not available to dealers in the U.S. until after April, 1972.[1] Strangely enough, Suzuki chose automobile race tracks to identify each of its 3 cylinder GT bikes for the North America market, i.e. 380 = Sebring, 550 = Indy, 750 = Le Mans.

Both the 380 and the 750 are far more popular restoration candidates and each of these models still commands a comparatively large following of faithful enthusiasts when compared to the 550. One drawback to the desirability of the 550, then and now, is its lack of a racing heritage. This is due, in large part, to the 550's unique engine displacement (nominally 543cc) which prevented it from competing in the very important 500cc class. Equally, the 550 could not compete in the 750 class because it would have been totally uncompetitive with the 750s of the day. Most collectors/restorers are drawn to bikes with a claim to racing fame in one form or another. Consequently, there are relatively few nice original or restored examples of the 550 around today, some 30+ years after the last 550 rolled off the assembly line in Hamamatsu.
A unique feature of the 550 (and its 380 brother) was its Ram Air cooling system for the one piece cylinder head. Two stroke engines lose power quite rapidly after the engine reaches its critical temperature, so Suzuki decided to try out an idea that had been used with some success on its 500cc two stroke twin cylinder racer, the TR500. This system consisted of a two piece aluminum shroud bolted to the cylinder head to duct ambient air over the cylinder head finning. The centre part of the head had an increased fin area and a larger shroud entry area in an effort to keep the centre cylinder running at the same temperature as the naturally more exposed outboard cylinders. In practice, it has been found that the centre cylinder actually runs somewhat cooler at speed than the outboard cylinders, so the system does work as intended. Another unique feature for its time was the Suzuki Recycle Injection

System (SRIS). This was the first attempt by anyone to reduce visible emissions from a two stroke motorcycle. It consisted of a small check valve in the bottom of each crank chamber. The logic behind this arrangement was that two strokes have a tendency to collect unburnt oil and gas in the bottom of the crank chamber at idle. Upon acceleration after a period of idling, the unburned oil and gas gets sucked up the transfer ports and contributes to an overrich mixture for the first 5 to 10 seconds resulting in a smokescreen from the exhaust. The SRIS plumbing routed the unburned gas and oil to the next cylinder in the firing order thus allowing it to mix more thoroughly with the incoming charge of that cylinder and lowering the production of visible smoke. Overall fuel and oil consumption was unchanged but visible smoke was greatly reduced on sudden acceleration from rest.[4] See the attached illustration for more details.

The exhaust itself was unusual for the time in that the centre exhaust header was split in two and exited into two mufflers much smaller than the single mufflers supplied for the two outboard cylinders. This gave a bike a nicely balanced look with two mufflers per side. The header pipes were all joined via balance tubes, known as Exhaust Coupler Tube System (ECTS), to increase low end torque. This feature was continued through to the end of production for the North American market but was dropped from the M model onwards in some other markets.

Suzuki had pioneered its version of automatic lubrication in 1966 to eliminate premixing of oil and gas as had been the norm for all two strokes up until then. This system was launched to eliminate the tendency of riders to run mixtures with far too much oil in an unnecessary effort to preclude engine seizures. The 550 had the latest version of this multipoint oil injection called Crankcase Cylinder Injection (CCI). This system was far superior to most of the competitors’ systems and used much less oil.

The 550 was, and is, a pleasant bike to ride with its long wheelbase and unstressed torquey engine. The engine will pull quite easily from ~3,500 RPM which was quite different from its competitors. Sometimes the rider has to stop and think whether he’s really riding a two stroke bike, rather than a four stroke. In part, this 'torquiness' is due to the undersquare engine design i.e. the cylinder bore (61mm) is a smaller dimension than the length of the crankshaft stroke (62mm). This type of undersquare engine configuration had long since been discarded for use in street bikes by most Japanese motorcycle engine designers due to its inherent limitations on power increases. Its incorporation into the 550's engine design was probably due to the particular 'character' that the designers wished the bike to have.

Electric start, plush seat, reasonable handling and comfortable suspension all make it suited for just about anything but racing. Medium speed highway jaunts are this bike’s strength, although you can hurl the bike into curves with some enthusiasm. All in all, a pleasant non-threatening middle weight motorcycle with only a smallish gas tank and somewhat limited lean clearance as caveats. Compared to its competitors, the 550 was a model of restraint and calm.
Ridden normally some owners claimed to see 40 - 45mpg (Imp. gallon), while others saw very different and heavy consumption, low 30's being normal and when ridden hard I personally once saw just under 17 mpg. Strangely the 550's heavy fuel consumption stands in contrast to the much more reasonable fuel consumption of the 380 and 750, both of which could easily return a regular 40+ mpg. Oil consumption, on the other hand, was miserly.
Specifications
• Engine type : Air cooled 3 cylinder two stroke with equal 120 deg. crank throws;rubber mountings for vibration reduction.
• Max. power : 48.5 HP @ 6500 RPM (SAE net, rated at the crankshaft) (36.1 kW); later models outside North America 53 HP
• Torque : 42.8 ft/lb @ 5000 RPM (58 Nm); later models outside North America 38.7ft/lb @ 6000RPM
• Induction system : Piston port w/3 Mikuni VM type round slide carburators
• Bore & stroke : 61 mm x 62 mm
• Displacement : 543cc (nominal)
• Compr. ratio : 6.7:1 (corrected)
• Ignition : Battery/coil with contact breakers
• Electrical system: 12 volt DC with 11 A-hr battery
• Charging system: 3 phase excited field type alternator w/max output of-
Nippon Denso = 28A @ 6000 RPM
Kokusan = 15.5 A @ 6000 RPM
• Transmission : 5 speed in unit, constant mesh, foot shift
• Final drive type : Heavy duty endless 530 chain
• Frame : All welded mild steel tubing; all tubes of circular x-section
• Dry weight : 441 lb. (200 kg)[5] Earlier models were rated at 418 lb (187 kg)[6]
• Overall length : 86.4" (2195 mm)
• Overall width : 32.1" (815 mm)
• Overall height : 45.7" (1160 mm)
• Wheelbase : 57.7" (1465 mm) nominal
• Ground clearance: 5.7" (145 mm)
• Fuel capacity : 3.3 Imperial gal. (15.0 litres) including reserve
• Brakes, front : 4LS twin panel drum (1972 MY only)
Single caliper hydraulic disc (subsequent MY)
• Brakes, rear : 1LS single panel drum
• Tire, front : 3.25 x 19
• Tire, rear : 4.00 x 18


Changes Year By Year

1972 Model (Suzuki MY designation “J”)
The GT550 introductory model was Suzuki’s counter to Kawasaki’s 500cc three cylinder street bike designated H1. Where the H1 was single minded and harsh, the 550 was broader in purpose and milder in tune. With its much broader supply of torque starting low in the rev range, the 550 would pull away from a stop quite easily from ~3000 RPM. The H1 had very little torque at this engine speed and had to be buzzed up to at least 5000 RPM before takeoff. With its longer wheelbase, the 550 was stable in corners and at speed whereas the H1 required an experienced rider under all conditions. Suzuki’s conservative design philosophy aimed to create a “gentleman’s tourer” rather than a “dragstrip burner” like the H1.
The initial model featured two striking paint schemes in the customer’s choice of Redondo Blue or Aztec Gold with tasteful contrasting striping on the tank and matching paint on the side covers.
Mechanical features included a massive four leading shoe double panel drum front brake shared with the GT750. The conventional telescopic front forks featured rubber gaiters covering the fork stanchions giving a somewhat dated appearance when compared to most competitors at this time. Both fenders were chromed steel. Chrome and polished aluminum were used tastefully on the rest of the bike. The gas cap was, unusually for the times, lockable and this feature was carried on through to the end of production. The rear turn signal lenses were red which, although unusual at this time, was not unheard of. Engine cooling was handled, of course, by the Ram Air system. First year sales were a very respectable 11,000+ units.

1973 Model (Suzuki MY designation “K”)
Two new paint and stripe schemes in Grace Lime Metallic and Hermosa Blue were featured for the annual model changeover.
A significant upgrade to the mechanicals appeared in the form of a single hydraulically operated front disk brake. The rest of the mechanical and trim items on the bike were carried over from the previous model.
Both the wheel and the other fork leg are capable of accepting another disc and caliper and a switch to a twin-disc front brake (like the GT750) was not an uncommon modification some owners made (although to be done correctly the larger master cylinder from the 750 was required). The single disk arrangement continued throughout the rest of the GT550's production.
For some reason Suzuki also chose to have the brake light operated only by the rear brake (in the UK market at least). A switch was available as a spare part to fit on to the front brake master cylinder casting which would also operate the brake light. The necessary wiring was already included on the main wiring harness in the headlamp shell. Thus the brake light would operate no matter which brake was used.
Unfortunately, while the new disk brake was perfectly acceptable in dry riding conditions, the same could not be said of wet-weather braking. In the rain, the disk brake was positively dangerous with an almost total lack of initial stopping power. Suzuki thoughtfully affixed a sticker to one of the fork sliders warning the rider of this fact. Fortunately the rear drum brake was very good.
This marginal braking setup was to plague the 550 (and all the disc braked motorcycles of the period) until the widespread adoption of the sintered brake pad in the mid 1970's. It took this advance in materials to finally make the use of stainless steel disks a less risky proposition on all bikes.This MY sales were 14,000+.

1974 Model (Suzuki MY designation “L”)
This MY saw significant changes, both mechanical and appearance-wise, to keep the 550 abreast of the competition. Again, two different paint and stripe schemes were offered with a striking “swoosh” decal on the gas tank. Choice of colours were Hawaii Green or Marble Scarlet. Some markets received a third choice of Stardust Silver Metallic in addition to the other two colours.
Gone was the rubber-gaitered front end, replaced by a cleaned up “Ceriani-style” set of forks. A touted benefit was better engine cooling but, with Ram Air, this was a non-issue for the most part. The three separate carburetors were gone, replaced by three “unitized” rack mounted items with a push-pull cable arrangement. Benefits mentioned were less of those costly carb balancing jobs and more accurate fuel metering. The handlebar mounted cable operated “choke” was gone, replaced by a lever mounted directly on the rack of carbs. The cylinder head and the Ram Air shroud were redesigned to cater for this new carb setup. The Ram Air shroud was now smoother and more modern looking without all the cast-in ribs of the previous two models.
Along with the new carburetor arrangement there came a new airbox and filter assembly. It featured bright chrome end caps for an attractive appearance upgrade and easier servicing of the filters. Along with the new airbox, the frame side covers were all new as well to blend in with the lines of the airbox end caps.
The chain guard was now chromed steel instead of the black enamel item from previous years. The shape of the guard was also updated. The red turn signal lenses had disappeared, never to return on any of the GT series thereafter. Some enthusiasts still bemoan the loss of those red lenses.
The instrument cluster still contained the speedometer and tachometer but a new item had been added. In another “first” for the motorcycle industry, Suzuki now supplied a digital gear indicator in the instrument cluster. There was a single digit LED number display in the centre of the instrument panel showing gear numbers 1 through 5 in a bright red colour. The neutral light indicator, however, was retained as a separate item.
This MY sales were 10,000+

1975 Model (Suzuki MY designation “M”)
Once again, two new paint schemes were featured to keep up appearances. Colour choices were Candy Orange or Gloss Black. Some markets received Candy Turquoise in lieu of Gloss Black. A more restrained striping scheme compared to the previous MY was in evidence, however.
The front forks were upgraded once again. However, the changes were mostly invisible to the average customer because the bulk of the changes were to the internal parts of the forks.
The Exhaust Coupler Tube System (ECTS) link between the exhaust pipes disappeared in some markets outside of North America. The North America marketing area kept the exhaust coupler tubes through to the end of production. Power is now up slightly (53 bhp instead of 48.5 bhp claimed) for some markets outside North America.
All other details were as per the previous MY machine. This MY sales were 14,000+.

1976 Model (Suzuki MY designation “A”)
1976 GT550A in Forest Green Metallic with optional factory parcel rack. Note Ram Air cooling shroud on top of the cylinder head.
Again, two new paint and striping schemes were introduced. Colour choices were Forest Green or Targa Red.
One major change to the “A” model was the introduction of composite lined cylinders with iron piston rings for the UK and European markets. This coating was marketed as 'SCEM (Suzuki Composite Electrochemical Material)'. Although not completely accurate this was more commonly known and referred to as a 'chrome plated bore'. For more information on this composite cylinder lining see the Wiki on Nikasil.
This was touted as a more durable arrangement with less repair costs when major servicing was required. Typical replacement costs were for new rings only rather than pistons, rings and reboring of the cylinder(s). The composite lining was supposed to last for the predicted life of the engine barring, of course, the effects of poor maintenance and/or abuse. Other benefits involved lower ring/cylinder wall friction for better efficiency along with better piston ring sealing capabilities. The GT550 was the only motorcycle, with the exception of the RE5 and a few RG500 racing machines, in Suzuki's lineup to receive this forward thinking feature. Many years would pass before Suzuki again used this type of rather expensive construction on a conventional road-going motorcycle.
The North American market machines carried on with chrome rings in iron linered cylinders.
Otherwise the 550 remained pretty much the same as per the previous MY machine. This MY sales were 9,000+.

1977 Model (Suzuki MY designation “B”)
The final 550 model again got two new paint and stripe schemes but the side covers were now only available in a semi-gloss black colour, regardless of what colour the tank was painted. The headlamp holders on both sides were also finished in black. Tank colours were Spark Silver or Uranos Blue.
The faces of the speedo and tachometer were changed from a blue background to brown thus matching the appearance of the instruments on the GS models. There must also have been a change in the plastic used as the 'glass' because it no longer developed serious opacity and cracks after long exposure to sunlight. Sadly the instruments did not get the appealing and then-unique 'rose coloured' back-lighting that the GS models had.
Trim items such as turn signals and taillight assembly were changed over to the same items as used on the newly introduced GS series of four stroke bikes. This was probably an effort to cut costs since Suzuki was in financial trouble at this time due to the vast amounts of capital invested in the ill-fated rotary engined RE5 motorcycle project.
One final item change was made to the front brake caliper. It now became a pivoting unit made by Asco rather than the fixed Tokico caliper that had been supplied from the introduction of the disk brake system.
The GT and GS series were sold side by side during this one year overlap. This was the last MY for GT550 production. Time had run out for two stroke street bikes. This MY sales were ~6,000+ making this the rarest of all the 550 models.


GT550 Engineering Changes And Modifications
01) From engine no. 23036 onwards: a new screw-in style of SRIS check valve was fitted to replace the original press fitted style
02) From engine no. 24552 onwards: a new spring type washer was fitted to retain the primary drive gear. Retrofitting earlier engines was recommended.
03) From engine no. 25054 onwards: a new hardened steel key was fitted to the primary drive gear. Retrofitting earlier engines was recommended.
04) From frame no. 32292 onwards: a revised front brake caliper piston, seals and brake pad set were fitted to alleviate brake disk squeaking.
05) From engine no. 27536 onwards: for Nippon Denso alternators only a new rotor with revised winding style was fitted. This was to prevent premature failure of the field windings and consequent loss of charging current.
06) From engine no. 32854 onwards: a new metal particle strainer was fitted to the SRIS check valves to replace the previous plastic items which had been found to melt in service.
07) From frame no. 36783 onwards: a new style of spark plug cap and insulator to prevent unwanted high tension current flashover to ground on the Ram Air shroud.
08) From frame no. 39304 onwards: a modified fuel petcock was fitted to prevent fuel starvation at high speed.
09) From frame no. 60143 onwards: a revised Ram Air shroud with new style spark plug caps was fitted to again try to finally cure unwanted high tension current flashover to the shroud under certain conditions.
10) From frame no. 60904 onward: a new style rear brake panel with wider brake shoes, a revised cam and arm are all fitted to improve rear braking performance.
11) From engine no. 63692 onwards: a completely revised Borg-Warner style starter clutch and associated parts were fitted to improve the durability of the starter clutch. Field experience had shown that the old style 3 roller starter clutch was not durable enough. This modification can be retrofitted to earlier bikes as necessary.
12) From frame no. 64337 onwards: a new style petcock lever seal was fitted to prevent fuel seepage from around the lever.
13) From engine no. 66724 onwards: a new style gear indicator switch was fitted. The crankcases were also revised to accept this new style switch along with additional parts to cater for the new switch.
This is a very short list when viewed against the number of changes made to other models, from both Suzuki and the competition. Considering that the 550 was produced over 6 MY and comprised over 60,000 examples, this list shows that the original design was quite well thought out

[oldjapanesebikes]

Excellent summation - thanks for sharing ! It is mentioned in the article, but just to repeat, from a distance the easiest way to distinguish the later European models from the North American ones is the change in the exhaust and the dropping of the cross couplers. Once you spot that, then take a closer look to confirm the type of barrel. I personally found the GT550 to almost be a nicer ride than the GT750 - close to the same power, narrower and less weight. Nice model.

[Alan H]

Thanks for that Russell, I've seen some of that before but not all in one place!
Regarding the red reflectors on the rear turn signals - they weren't on my 550 in 1972. Those were definitely orange and I still have the pics from then!
I had a go on my mate's GT750 A many years ago (when it was new) and I really did like that model - far better than the earlier 750J in my mind. Lovely engine but mediocre handling that one.
The 550 was easier to handle than the 750 due really to the difference in weight, but both nice bikes.
The A was what the J should have been, a proper beast and would handle too. I really did fancy one of those. Maybe one day.......
The 550 was a tad low, I scraped on the way home the day I bought it, but I sharpened up the handling with Duckhams in the forks, and a 19" back wheel. The centre stand went in the back of the shed too in the interests of my safety - I did ride 'hard' in those days when I was 21 and invulnerable. The engine was well tweaked too.
Thanks for the inputs, any other info will always be appreciated.
I wish I could find out who owns the blue 550J I saw a couple of weeks ago locally, he can't frequent this forum at any rate.

Regarding the comments in the write up of no racing heritage, I saw a Crooks 550 at (I think) Oulton in 1973 taking Commandos on corners, before he dropped it in front of me! It was all I could do to restrain myself from running over and having some bits off!!

those really were 'the good old days'.

[mark.read3]

Think i'll move this one into the 550 section, well worth keeping.

[Alan H]

Good info there Glenn. Thanks.
Excellent idea Mark. Just so I can find it next time!!!

Alan