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Forgot to mention something very important. The amount of preload on the suspension springs affects the unladen sag. This can change some dimensions noticeably. When I use photogrammetry for such measurements, I make sure the suspension is topped out at both ends. This obviously does not represent real world conditions, but it makes for consistent measurements between bikes.

A lot of factors go into making an accurate compression test. A few things to think about: Compression must be tested with the throttle held wide open. I usually keep kicking until the gauge stop rising. This can often be a dozen kicks. The spark plug adapter you use can make a big difference if it increases the combustion chamber volume appreciably. For example, using a short-reach adapter in a long reach plug hole gives inaccurate (low) readings. If the piston crown and/or combustion chamber has a large about of carbon buildup, this will increase the reading. Smaller cylinders tend to have higher cranking pressure than larger ones. The barometric pressure (altitude) will affect the exact number. A hot motor will make more cranking pressure than a cold motor. Oily cylinders tend to make more pressure than dry ones due to a better ring seal. There are other factors too.

I have not yet watched this 50-minute video on trials bike chassis geometry, but at about 4.5 minutes he touches on the 2023 GasGas versus Sherco. https://youtu.be/skK-R6nT4eM After watching as much of this as I can stand (about 30 minutes) I'll throw out the following for your consideration: 1. The analysis is made in real time. I would have preferred it be made off-line and just the findings reported. 2. The analysis assumes perfect scaling of the photos. Although the scaling may be “good”, sometimes you are looking for subtle differences between the bikes. 3. The reviewer is a big guy (250 pounds = 113 kilograms) and I expect this skews his riding impressions. 4. Similarly, the reviewer seems like more a trail rider than a competition rider. I think a better method would be to take the same photos and use a free photogrammetry tool like https://eleif.net/photomeasure That, and a known wheelbase, would allow you to make comparative measurements of various points on the bikes and enter all the data into a spreadsheet.

How much longer is the wheelbase? EDIT: I just read this in the 2023 TXT owner's manual: Wheelbase 1,320 ± 10 mm (51.97 ± 0.39 in)

well, I guess I should say that I like having the bars somewhat a bit forward of neutral as it helps with leverage over front end... bar risers and taller bars generally shift the leverage point/. Also 23+ the gasgas comes with pretty tall bars as they triple clamp height and mount is somewhat lower that what you usually see on trials. I should clarify a bit - I guess I was inquiring moreso to the overall impression of others of this 23+ gasgas as compared to other brands - the wheelbase is longer for the bike than a couple of other trials bikes I have been on and by extension the reach is longer - swingarm to pegs seems the same as most trials bikes (about 40cm iirc)

I agree with lemur. But in addition, just rotating the bars fore/aft can have a big effect. A set of “bar risers” is also a possibility.

Reach implies arm position so height and position of your bars is where you would adjust for reach, a set of taller bars aka 'indoor bars' is a good investment and will fit both bikes, had them on one of 2 rides and it makes a surprising difference in leverage and riding position.

Just got a new Gasgas, coming from a 23 sherco, I had an opportunity of a really good deal on a brand new Gasgas so I want to try that and sell whichever one I like riding less. The gasgas is so much longer than the sherco, the reach seems quite a bit longer. For guys that have ridden a bunch of different trials bikes, you guys find that? How did you adjust?

So you are scratching up your fresh new spray coat of ultra hard nickel and silicon carbide that is actually harder then your piston rings for what purpose 🤔

Hello guys, I've got an engine for my Ossa project... comes from a late 70s Pioneer, I think, as it's got the coarse teeth on kickstarter and gear lever. The engine starts but it's drinking gearbox oil, I think... it's impossible to jet and smokes bad. The smoke is also very dense and isn't easy on the throat. I asked several shops... some will do it but I'd have to ship the whole engine block. Some others won't touch it with a 2 meters pole (most of them). I've just bought a Beta M27x1.25 puller for the flywheel and plan to get a bearing puller to grab the cush drive. The good thing is, I have an Explorer engine partially seized I can experiment on, before I work on the good one. Also think I've found the seals measurements. The Motoplat stator should be good on both engines, so might end up selling the one on the partially-seized Explorer engine. Is it worth disassembling completely or best kept in one piece with head and cylinder still in place?

Plus, fit a decompressor which makes kicking even easier 😂

Just airing this to see what you think , ran a Compression Test on my Techno 97 and got nigh on 170 PSI , whan I had the exhaust off I took a look at the piston and it looked worn and scored but this bike seems to have a lot of compression whn kicking it over and seems to pull very very well low down. Tried a 2014 Evo 250 and only go 110 PSI well it was more like 106 but I rounded up, is this right? I know it all depends on the life that the engine has had but I would have expected it to be the other way round with more compression from the Evo, the Evo does sound a little slappy like th little end is starting to knock so its goinf to have the head off for inspection at some point.. I must say the Evo controls all work perfectly compared to the Techno , brakes particulary but I guess if the Evo motor is good it should pull hard in all gears even the high rato 4 and 5 but its difficult to test round where I live as the bike is not road legal. Is there any road test I could do to test the motor out as I dont want to DNF because of the motor notfiring up or not pulling up a hill in a wet soggy trial New Years trial I'm thinkin of entering. TIA

Thanks for the picture! I understand what the split spanner and the bigger "bushing" are for... but what about the smaller/taller one? What about a bearing puller like this one? https://www.amazon.it/VEVOR-Estrazione-Cuscinetti-Separatore-Autoveicoli/dp/B0FNNLQKQG/ref=sr_1_32?__mk_it_IT=ÅMÅŽÕÑ&crid=1J9OT632AEQI4&dib=eyJ2IjoiMSJ9.F7DabM4KgRoeLNC5m87AKWI_81P6lH4H-JJv9hmS54VsgH7Jl2H_sBto6YefSEh2Mr323F-rM-F6YW7kURCX9k4AS5nS0TQq7oseyI-y_6tyoIFOlLERt7evmcUJ3FppwkGGwQj942Cg5GP412S4qc2SW3V26VtVvBueYD8eTEv9qbVyeMNwz6EW76d88atoDXLtvB6dwI508tvq0yavbEFXIFUbUhArl26l9Kup6xcINWcCpPb23ntBHz3ppRigPMkKMroC5-emTMg1sGRRxL5fJcUrS9xzKy0T9G8Bdr0.Ij-6NlEcHc2accfls-XnAXjYLpCaYct6YzIU-jgxHC0&dib_tag=se&keywords=estrattore+cuscinetti&qid=1766358853&sprefix=estrattore+cuscinett%2Caps%2C315&sr=8-32 I think the flywheel needs a puller M27x1.25, right? I can easily find one locally. Do you remember the measurements of the seals, by chance?

I've had a few plated dirtbikes & have given them a light hone before installing a new piston & rings, i know a lot of other Blokes that have done the same, as long as the mechanic has the correct tool & knows what he is doing there should be no problems.

I’ve exceeded my limit more to come later

Here’s another pic. More to come

Here’s some pics

When a piston ring pack becomes gummed up from bad fuel the rings stick in the piston grooves, then everything starts to go badly. Once you experience it you will know why I call it a jam sandwich.

Lemur what do you mean with jam sandwich?

I’ll take some pics of both tomorrow.

Thank you!

I’d be checking the internal diameter of the con rod small end. Even with the slightest play it will give a knocking noise. The piston doesn’t do much other than support the rings, which do all the hard work and wear considerably. If the con rod is slightly out of specification everything will wear as it won’t be runnng true and it will do the same again

You can use the TY175 head or the DT175 head. If you use a DT175 head, the compression ratio will be higher but you may need to trim the head fins for exhaust pipe clearance. You can mount a clutch cable holder on the engine casing or on the bottom cylinder fin. The DT175 cylinder fins will not interfere with anything physically. Trim them if retaining the original TY appearance is important to you.