Tomas ST 2008 and 2012 engine differences

2008TomasSTSpeedometer.JPG
2012TomasSTSpeedometer.JPG

I was helping a friend assemble his A55 engine that belongs in his 2012 Tomos ST that he bought new in 2013. We found that the four stud holes in the head gasket were too small for the size of the studs in the engine. A 2008 Tomas A55 has M6 studs, and his 2012 has larger studs, I think M8, maybe M7. There is a clue in the parts manual:

233716 CYLINDER STUD BOLT M6/M7X115

236639 NUT M6-8 DIN 986 A2F

I think maybe the nut designation may mean either M6 or M8? The stud size is hard to figure out as it might be that one end is M7, the other M6? There doesn't seem to be M8 in the stud designation in the parts manual.

In any event, the 2012 was bought new, and the studs were installed at the Tomas factory. My friend says the 2012 easily gets to 40 mph, while a 2008 with M6 studs will get to about 34 mph. The larger studs in his engine make me think the 2012 has more horsepower than the 2008, and perhaps heavier studs were necessary. The 2008 speedometer goes to 40 mph, his 2012 goes to 60 mph. My question is, was the change in engine studs and speedometer simply a model year change, and if so, in what year was the change made? Thanks in advance.

Re: Tomas ST 2008 and 2012 engine differences

yeah m7 on one end, m6 on the other. should be that way for all a55 engines (fancy models after 03(?) and ALL tomos after 06)

I don't know that they changed much, I know the early ones after the 2017 comeback had ignition issues that got remedied later

but afaik '08 and '12 shoulda been pretty much identical, except just standard differences like kick vs pedal, oil injected or not, wide rear tire versions, electric start, or silver vs black sidecovers.

Re: Tomas ST 2008 and 2012 engine differences

I hear you, but they are not the same.. the head gasket needs to be different on the 2012 with larger stud holes, the top speed of the 2012 engine is faster, and the speedometers are clearly different. The nuts that hold the head on are larger on the 2012, and not 10mm hex as on the 2008. The threads on the top side of the 2008 studs are M6, and the 2012 studs are larger, I think M8. I guess it might be related to configuration, as the 2008 I am looking at is a kicker and the 2012 is a pedal. Both are oil injected, and neither has electric start. I will have to go back and look at the 2012 to see if the head nuts are M7 or M8.

Re: Tomas ST 2008 and 2012 engine differences

Why not pull the top ends on both ? Compare boost and transfers . Do a port map for each . Compare port shapes and sizes . Compare pistons and head configurations .

That should tell you a pretty good story .

Then you can post results here and everyone will know . ;)

Re: Tomas ST 2008 and 2012 engine differences

Overpriced Parts /

Stud size has nothing to do with horsepower,

He could’ve had a kit, a reed cylinder or ported cylinder on there, maybe a performance pipe or filter instead of stock different gearing, different carburetor, different intake, tuned/jetted better or the speedometer could be off/jumpy/most times tomos speedos are off with 16inch wheels (whereas I’ve found the tube frame tomos like revival with 17inch front wheel are closer to true)

My 06 kick start revival has a different stock pipe that exits on top then newer ones they changed to bottom exit (so it don’t block up with oil carbon as easy) and it came stock with a 58 jet instead of a 55 so it was a mile or so faster then my friends 08 pedal start stock for stock but not 6mph,

On a a55 cylinder ring replacement should be at 5k mi for best performance (and decarbonized even sooner) and stock pipes the (ones come with catalytic converter) block up after a few thousand miles too so there’s so many factors but stud size has nothing to do with the horsepower unless changed to accommodate a different aftermarket cylinder,

Re: Tomas ST 2008 and 2012 engine differences

The 2008 has had the speedometer changed, it should have a white 40mph speedometer. The speedometer on there is from 1992-2002. There shouldn't be any real internal differences other than different suppliers for various parts. Both would have had the same top speed off the showroom floor. Chances are the faster bike has had some work done to it. Probably gearing. The a55 studs that are m6 on top and m7 on the bottom are kind of pointless so it wouldn't surprise me if tomos ditched them for straight m7 studs.

Re: Tomas ST 2008 and 2012 engine differences

Lots of good information, but my original question remains, that is "was the change in engine studs and speedometer simply a model year change, and if so, in what year was the change made?"

I thought I made it clear, but to make sure, the 2012 ST pedal is absolutely the way it came from the factory. It has never been modified. It has larger head nuts and studs than my two 2008 ST kickers. Also clear is that the top speed of the 2012 is significantly higher than the 2008s.

"Stud size has nothing to do with horsepower". I don't agree. I think it is possible that the 2012 engine has higher compression and/or more horsepower, and Tomos may have decided that heavier studs were needed. Or, perhaps, the engine internals are the same, but Tomos decided to heavy up the studs for another reason. To me, if the factory changed stud size after many years of the same design, then perhaps the 2012 engine has more horsepower than the 2008. Alternatively, I guess it is possible the gearing could be different in the 2012, and that may put more stress on the engine, and Tomos decided to use heavier studs for that reason even though there was no horsepower change.

Both of my 2008s have black speedometers, but that doesn't mean they are original, so I accept that they should be white. White or black, the 2008 would have a 40 mph speedometer, while the 2012 has a 60 mph speedometer. The sub question is, in what model year, did Tomos change from 40 mph speedometers to 60 mph speedometers in the ST line?

Re: Tomas ST 2008 and 2012 engine differences

my tomos speedos r consistantly off by 7 or more mph. way past 40 but really just breaking 35, gotta gps for acurracy, never seen a 60 mph or km speedo. anyways just ditch your head gasket that doesnt fit, it not necessary if u know what your doing.

Re: Tomas ST 2008 and 2012 engine differences

Anyway order a set of metric punches. Whack the paper gasket over a piece of cardboard so as not to dull the punch. Alternatively use a small Dremel bit but the punch is betta.

Re: Tomas ST 2008 and 2012 engine differences

Overpriced Parts /

> Von Zy Wrote:

> -------------------------------------------------------

> Lots of good information, but my original question remains, that is "was

> the change in engine studs and speedometer simply a model year change,

> and if so, in what year was the change made?"

>

> I thought I made it clear, but to make sure, the 2012 ST pedal is

> absolutely the way it came from the factory. It has never been

> modified. It has larger head nuts and studs than my two 2008 ST

> kickers. Also clear is that the top speed of the 2012 is significantly

> higher than the 2008s.

>

> "Stud size has nothing to do with horsepower". I don't agree. I think

> it is possible that the 2012 engine has higher compression and/or more

> horsepower, and Tomos may have decided that heavier studs were needed.

> Or, perhaps, the engine internals are the same, but Tomos decided to

> heavy up the studs for another reason. To me, if the factory changed

> stud size after many years of the same design, then perhaps the 2012

> engine has more horsepower than the 2008. Alternatively, I guess it is

> possible the gearing could be different in the 2012, and that may put

> more stress on the engine, and Tomos decided to use heavier studs for

> that reason even though there was no horsepower change.

>

> Both of my 2008s have black speedometers, but that doesn't mean they are

> original, so I accept that they should be white. White or black, the

> 2008 would have a 40 mph speedometer, while the 2012 has a 60 mph

> speedometer. The sub question is, in what model year, did Tomos change

> from 40 mph speedometers to 60 mph speedometers in the ST line?

My 06 a55 has higher compression, bigger jet then both 2008 or 2012, and is a bit faster than both of those so there’s something wrong with the speedometer or tuning or something blocked because I beat both of those stock for stock by a mi or so

Post roadside radar video of both,

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