This topic was posted as a question early this year and it seemed like a good bit to include in my trip this winter. Unfortunately it appears the post has been deleted as numerous HUBB searches have failed to find it recently. I don´t know who the original post was from nor can I remember the names of respondents.Before it disappeared the replies concluded that there were two crossings of the Rio Ucumacinta, at Frontera Corozal and Benemerito de las Americas , which both involved much struggle with getting on and off the small boats and up steap riverbanks-- possible but impractical. The third crosssing which was reported by another poster who had done it involved a land route southeast of Tenosique, Tabasco but left some unanswered questions.
From field research in the past week I can now affirm that the land route does indeed exist ...BUT... it is good for dry weather only as it consists of only a set of 4WD (?) ruts wandering about in the grass, rocks and topsoil between two fencerows. The Mexican road from Tenosique is good quality pavement 60km southeast out of town to the border crossing called El Ceibo, almost exactly in the 90 degree angle made by the border and on the south bank of the Rio San Pedro. .The Mexican customs post there is open 9 am to 5 pm , 7 days a week. The Guatemala side has NO customs post at the border . The Guatemalan paperwork must all be completed after traversing the 22km to the town of El Naranjo where there is the customs office in town. From El Naranjo the road is again excellent pavement of recent construction, connecting to pavement to Coban and Flores etc.
There are some 12 small inexpensive hotels in El Naranjo which do a good business serving a steady stream of illegal immigrants who can be seen diving off the road into the brush in Mexico as one approaches .Virtually all the traffic to the border in Guatemala is via launches on the Rio San Pedro, even some larger cargo boats capable of carrying 22 tons of sand exist, again a boat trip may be possible here too.
The scenic route from Palenque to this crossing , all pavement, consists of going south from Palenque on Mex 199, turn east onto Mex 307 , then at Rio Chancala turn north to Gregorio Mendez then Mex 203 east to Tenosique(hotels) and to the border at El Ceibo.Alternately ,take the short state route to Emiliano Zapata , off Mex 199 north of Palenque, and then mex 203 to Tenosique, etc.
The day I got to the border it had rained overnight and after bumping across the protruding bedrock and mud hill which passes for the main street I saw 500m outside of the Guatemalan village that NOOOO WAY was I going to even try getting my R1100GS on street tires through that mess. A minor detour involving a ride to Chetumal, then through Belize and west though Guatemala got me to El Naranjo anyway 3 days later.Investigation there showed that the mud track extends to within 3km of town before turning into rough gravel.
If only the entire road was like that .As it is now it would be best to wait at least two days after a rain to let the mud dry up some and the puddles to drain. It can rain here any day of the year.Off- road tires would be a definite asset, or group travel to dig one another out.
South of Tenosique there are two other small border road crossings, at the end of gravel roads at hamlets called San Francisco (east) and Corregidora Ortiz Neither has any form of customs for either country, gravel 7 dirt roades continue in Guatemala. One could ride dual purpose bikes in and out with no paperwork e.g. to see the archaeologic site of Piedras Negras.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93