XT/TT/SR500 Differences

[Tahitian_Red]

What are the differences between Yamaha's three models of 500 Thumpers?  Gear ratios? Heads? Cams?

[SON]

Don't forget Ignitions and Valve sizes,
Red you might be better off asking what you want you want your engine to end up doing?
And of course you being able to start it.
The Brains Trust can kick in from there
I have a 540, 560 and a 605
Funnily enough the stock bore and stroke is easiest to start.

[Tahitian_Red]

Gonna run stock, but wondering which would be the best to start an MX project with?

[Simo63]

I had an SR500 powered HL Tribute bike (not really a replica).  The SR motor has bigger valves fitted standard but they are easy to have fitted to your TT/XT head.  The real benefit/difference was the 12 volt electronic ignition. Starting was a 1 kick affair, no kick back and it always ran strong.

Just my experience.

[Tahitian_Red]

Are the gear ratios in the SR different than the TT?

I thought Hallman and Eneqvist used an XT motor in the first HL's. 

[Paul552]

is the XT frame and SR frame the same? It looks similar except from the hoop at the back and the peg location.

[curly001]

The Sr frame is totally different.
The Sr head was bigger in the finning and had a 49mm inlet as apposed to the 47mm in the XT/TT
The later model XT's had the same head/valves as SR
The SR had 12volt cdi ignition
The XT/TT had points ignition. The XT had 6volt lighting, the TT had optional lighting(not the same as XT)
The gear box ratios are all the same
The XT/TT frames are the same except for a few brackets. ( Different rear mudguards & and rear brake set up)
The XT/TT frames, tank, triple tree/forks and front brake changed in 79
The engines are basically the same except the clutch side cover is different due to different ignition
There were changes to the oil pump, selector drum & oil feed pipe over the course of the model run.
Now what to start with? All depends on what you want to do.
Leave that for another post
Curly (note this isn't everything but is a basic outline)

[jimg1au]

i was told that the early sr500s have bigger flywheels.
usa flattrack guys love them

[curly001]

Jim, if you mean crank wheels the 78TT had lighter cranks. The fly wheels are all the same Dia. Curly

[jimg1au]

the guys on the flattrack fourm in the usa say the first sr500s made had bigger heavyer flywheels of the same year tt and xt.j2j prefix.only.they use them in there hot rod flattrack bikes with pvl ignitions with outside fly wheel weight on the little pvl intenal rotor.i have such an ignition setup.early sr fly wheels (crank) wont fit into early tt or xt crankcases.later are all the same.
i have 2 very early sr500 engines from the usa might check that story out one day.
jim

[GMC]

What Curly said, plus…
All TT’s, XT’s & SR’s had the same size exhaust valve
It was only the intake that was bigger on the SR’s but the G /H model TT & XT also had the bigger intake valve

Part # = 583-81350-50-00
Part Description = ROTOR COMPLETE
Model Count = 6
TT500C 1976 500 TT500 Off-Road
TT500D 1977 500 TT500 Off-Road
TT500F 1979 500 TT500 Off-Road
TT500G 1980 500 TT500 Off-Road
TT500H 1981 500 TT500 Off-Road
XT500C 1976 500 XT500 Dual Purpose

Part # = 583-81621-50-00
Part Description = CONTACT BREAKER ASSEMBLY
Model Count = 10
TT500C 1976 500 TT500 Off-Road
TT500D 1977 500 TT500 Off-Road
TT500F 1979 500 TT500 Off-Road
TT500G 1980 500 TT500 Off-Road
TT500H 1981 500 TT500 Off-Road
XT500C 1976 500 XT500 Dual Purpose
XT500D 1977 500 XT500 Dual Purpose
XT500E 1978 500 XT500 Dual Purpose
XT500E-205001 1978 500 XT500 Dual Purpose
XT500F 1979 500 XT500 Dual Purpose

The others had electronic ignitions and from memory there are 4 different types of electronic ignitions between the 3 models and I am led to believe you can’t mix and match parts from the 4 different ignitions

[curly001]

In a Australia only the Sr's had CDI in the States and some Euro countries the XT's had CDI but it was 6volt. The SR CDI has numerous versions and are not interchangeable( In OZ we had 2 versions)
As for cranks once the SR was introduced the cranks were the same. Only the early TT's where lighter, which is what the boys in the states would of been using as the TT was more prevalent than the XT there untill the release of the SR.
Curly.

[Frank M]

As for cranks once the SR was introduced the cranks were the same.

Partno. Crank SR500
SR500E   1978      Crankshaft assy 2J2-11400-00-00   Crank right 2J2-11412-00-00       Crank left 2J2-11412-00-00
SR500F   1979      Crankshaft assy 2J2-11400-00-00   Crank right 2J2-11422-00-00       Crank left 2J2-11412-00-00
SR500G   1980 ->   Crankshaft assy 583-11400-09-00   Crank right 583-11422-00-00       Crank left 583-11412-00-00

The crank of the first SR had a slightly bigger diameter.  A 1978 crank will not fit in a 1980 case without modification of the oil gallerie.

[cloggy]

 As far as I've read the later heavy SR flywheel will fit into the early cases with a touch of grinding. Some people prefer the later crank in mud [ie UK] The later valve will fit straight into a recut inlet seat
 On the later bikes the clutch is stronger, the oil pump is a five bolt fitment and the gear change mech runs on a bearing
 In the real world none of this seems to matter much. The only thing that seems to be a no no is using the SR frame offroad, it's supposed to be weak.
 The TT is supposed to have a 34 inlet stub. The XT and SR are said to be 32 and restrictive
One mod is to use the 36mm XS650 inlet stub.
The TT doesn't have a tacho so there's more meat round the intake, which is only relevant if you really know what you're doing [as opposed to just thinking that you do]. From what I've read I'd keep well clear.
I've no idea what my 76 TT engine has, it won a lot of races in more capable hands than mine, so I'll leave it alone. I have fine tuned the 38mm carb and sorted the exhaust. Total length is supposed to be around 36".

[Husky500evo]

The clutch basket on the SR motors is more heavy duty, with a steel band around the outside. The XT/TT clutch cover won't fit over an SR clutch. I had a couple of SR motors that I used in Formula 500 speedway cars a long time ago. I converted the SR motors back to points ignition, by having the right side crankcase drilled to take the XT points drive gear and used an XT clutch and clutch cover, as the SR's CDI stators are notorious for failing. I also had the motors through bolted , as I had trouble breaking the cylinders when using high compression pistons and methanol.