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Hi Ross, I've written technical articles for a Trials publication here in the U.S. for about 12 years now (as a volunteer, not paid, I just love technical stuff and like to share my experience) and a little while ago I wrote about the sidevalve engine: a link to it is here http://www.gasgas.com/docs/gg_4str_stood.pdf and that may answer some questions. If it does not pass the filtering process, PM me and I'll send you the link. Jon

TrialsPartsUSA: http://www.trialspartsusa.com/tech.html has downloadable parts and owner's manuals for your Pampera that should help. Jon

Ross, A little with the Harley's, but a lot with the V8 Ford/Merc's Hudson Hornet's etc., including the little Ford V8-60 used in mini-sprints of the time. For top-end HP, it was hard to beat the overheads as I found with an ARDUN conversion for one of the flatheads I built. As I remember, Zora Arkus (father of the Corvette) built the ARDUN conversions for trucks at the time but we soon found they were a welcome addition for power-hungry geeks like me. I would imagine the V8-60 is fairly rare nowadays, I think they only made them for a year or two in the early 40's. Ah, the good ole days (actually things are a LOT better now!). Jon

I haven't heard of anything lately. Last I knew, they had hired another design engineer, from France as I remember, and were changing valve size and sparkplug placement in the head, both very critical in a sidevalve engine. The plug placement is important due to the combustion chamber shape and size and where the plug is located will determine flame front propagation and burn pattern. When I raced the sidevalves in the 50's, we tried to treat the piston crown as one large squishband. The area over the valves is a constant due to having to have the clearance for the valves to open. The little buggers could make a bunch of power if they were built correctly. I'm handling tech inspection at the U.S. National this weekend so I'll try to collar Dale and find out the latest on it's development. My guess is the problem was the economy rather than technical difficulties. Should work well if properly developed and I understand the engine only weighed a kilo or two more than the 2T Pro. Jon

I surely can agree with that. I imagine that it's a "guy thing" and we hate to ask for (or read) directions. Jon

Actually, over the years I've had pretty good results with the Wiseco pistons, provided proper set-up and break-in proceedures are adhered to. Then again, I find it hard to believe a piston company established in 1941 could remain successful today by making "total junk". Jon

My guess it that it's a maintenance problem directly related to that particular bike. All the Beta four-strokes I've come across have been easy starters and essentially trouble-free. I think that it's difficult to compare the reliability/maintenance schedule of the four-stroke used in Trials to that of the much more stressful environment of MX and Roadrace. The oversquare (bigger bore than stroke) design used now does not lend itself to a lot of piston skirt surface area so one has to be careful as to piston replacement intervals. The much higher RPMs encountered in other forms of motorsports does make it rough on the slipper-type pistons and when the skirt wears beyond service limit (the skirt is fairly short), it leads to "piston rock" which will cut a gouge at the upper, front part of the cylinder (the "thrust side") and the cylinder will need to be replaced. With the lower RPMs encountered in Trials, I would think that, with proper maintenance, the four-stroke will have an extended life when compared to other four-strokes in other forms of competition. Jon

Yipes! Yea, Copey and Feetupfun are right. I just caught this thread and when I saw the cut valve shim for a key I figured I'd better chime in. I would guess that most riders don't know that the Woodruff key is only for alignment during assembly and does not hold the flywheel in alignment. The special tapers of the flywheel hub and the crank snout (a "Morse Taper") is what makes them "stick together" (also called an interference fit). You could make a key out of hard plastic and it would still do it's job, probably better, as it would not scar the taper surface if the hub spun on the snout. I'd advise that the shim key be removed and you could file one down from a small piece of mild steel strap, which would be pretty close to the OEM one (I've had to do this more than once). If the flywheel comes loose, the shim key will possibly cause some severe damage to the taper surfaces and possibly other components. Jon

I spoke with a retired machinist friend who has several top-notch Bultacos (stock, modified frame and a Sammy Miller framed example) and is an expert on rebuilding the Bul engines. He said he sets up shirt clearance at .0015" and has never had a problem. I really trust his judgement so this is why I passed on that recommendation. On the subject of port chamfering, I often see the port edge cut sharply at a thin, 45 degree angle (just enough to "break the edge", as some machinists say), which will keep the ring edge from catching, but promotes damaging harmonics and wear by slamming the ring back into the land, and in a place where the ring experiences the most heat. In my experience, a better way (using an exhaust port for an example) is to use a 15-18 degree angle with the chamfer about 2-2.5mm in width in the top/center of the port and tapering out to the edges. This way the ring is eased back into the ring land, rather than slammed back when it catches the center of the 45 degree slope. This type of chamfering is mandatory in a roadrace engine, for instance, with big ports, high RPM and high heat, but I've found it promotes longer ring life in any two-stroke. Intake ports are a little less critical as they are usually narrower and have the cooling effect of the intake charge, but I think you'll get the idea. Jon

It's been a while since I had my Bultaco, but I'm with Stork on this. .0015" is a somewhat standard spec., providing the cylinder is prepped correctly (specifically 15 degree port edge chamfering and correct cross-hatch patterning). Since you are going 340cc's, a consideration will be the type of piston used as a forged piston will expand a little more than a cast one (proper break-in is a little more important with a forged piston). I like to run the engine through a couple of heat/cool cycles and check all the fasteners. Then, with a tad more rich premix ratio, run the bike through an easy section (low RPM and no hard pulls) to help seat the rings and bed-in the piston a little. The on/off, light pull throttle applications, keeping an eye on engine heat, are important. I just did some prep work on a new 2010 280 and the clearance miked out to .0015" using a forged Vertex piston. Jon

After checking the usual possibilities like air cleaner, electrical connections, water in fuel etc., you may also want to check the valve clearances if you are bumping the rev limiter often. The DOHC's will commonly recede the valves slightly with high-RPM use, enough to close up the clearances and affect cam timing/valve sealing. A lot of us "old timers" would expect the four-strokes to get noisier if clearances are off, but a lot of the modern OHC/DOHC engines actually get quieter as valve/seat wear causes clearances to get tighter rather than looser. Jon

In my experience, center case gaskets are installed "dry". For cases that require a sealer, I use Yamabond-4, which is specifically intended for center case sealing. Jon

Another link for all things GasGas: http://www.trialspartsusa.com/tech.html Jon

His sections were very good. Lots of cleans on Saturday and some tougher ones on Sunday to pull the scores out a little and not have as many clean-loop cards. Every section I saw had several lines and so rather than just go from one obstacle to another, if you took the time to really observe, you could make choices and map your way through the section. Nothing hard on the bikes or riders and they were fun to ride. After the Trial, I went out and rode several just for kicks. Jon

That's my guess also. I can think of few things that would totally lock up a brake, cause drag maybe, but not lock it up. If the adjustment is in too far, it's a closed system and that would lock the brake when the fluid expands with heat. If that's the case, I would think it would release (and probably drag some) when the fluid cools off. The lack of freeplay is a very common problem with riders that come from cable systems to hydraulic. Jon

It's amazing how many sections are on a short loop at Tish. I'm really looking forward to the new riders to show up for the National, they will have a good time. Glad you like the sections, you have a good eye for what the "challenge level" should be, the sections at the AHRMA National were great! Jon

Ed, Let me know if you have any problems with the TY. I'm sending some vintage DVDs to your home so you'll have something to watch when you get a chance to rest from all the running around you and Evelyn do. Have a safe trip. Jon

Let's just say, when the blue Triumph Cub came through the sections, they were insect-free. The owner was very enjoyable to talk with and really put his heart into his riding and was having as much fun as anyone out there. If all the AHRMA events are as fun as this one was, I'm going to try to talk Graham Foster out of his Ariel and take up Vintage riding....... Jon

I'll be going down to Tish for the Rock Creek national (I'll be handling tech inspection for some reason) and as far as I know we will be using the new "Clubman" line. As we're the first Trial of the season, it will be very interesting as to how it works. I personally think it's a great idea and should open up competition for new riders who otherwise would not try a National event plus allow twinshocks to compete. I remember, as a noobie in the 70's, I signed up for my very first Trial at Hollister Hills in Northern California and found it pretty tough, but I did finish, sore and tired. Only later did I find out I had entered a U.S. National........ Jon

There were a couple of "less than perfect" bikes and one Cub put out enough smoke to kill any mosquito within a mile, but these guys obviously love their bikes and keep them in top shape. They also are willing to plow them over rocks and through mud bogs so you never see any "trailer queen" bikes in this group. There were a couple of young guys, but most riders were of the "vintage" class themselves, you might say. We have a lot of custom cars and hotrods on the streets here in the Midwest, and most of the drivers I see have grey hair so I'm guessing that it's kinda the same in AHRMA and we're finally getting to ride the bikes we couldn't afford as kids..... Jon

It's tough to beat the fun level of a Vintage Trial, let alone the wonderful sounds all around one. Randy Black from Kansas brought his nice 441 BSA and also one of his present projects, the TLR250, which I rode. Great bike, very smooth and handles really well. The weather and venue was perfect and everybody had big smiles both days. Jon

A few more

Some photos from this weekends AHRMA National at the Jordan Valley Ranch. Evelyn and Ed Peacock and Hugh Campbell set up the sections, which were perfect. Jon

Sam, I kinda wanted to stay out of this discussion, but in my experience, the bike shop is giving you good advice. The 2 gaskets (some engines come with one or rarely three, the thickness of the gasket(s) is much more important than the number of gaskets, which come in various thickness spec.'s) are used by the assembling tech at the factory to set squish band minimum clearance. If you remove one you may run into the problem of reducing the squish clearance to the point that, under operating condition temperature and material growth, you may have contact between the outer piston crown and the head. Contact at the outer crown will reduce top ring land clearance and cause the ring to seize in the groove, causing blowby and a spike in piston skirt temps and skirt deformation. Things go rapidly downhill fast from there. Jon ps. Forgot to add that it would be a good idea to check the squish clearance just to be sure. Soft solder works well and to be really accurate, use two pieces, front and rear, which will compensate for piston rock. Generally accepted clearance is about 1mm (.039"), but the 125 can get away will a little less as smaller cylinders have a little less temp growth of components.