Re: Tilt/Trim cap seal and ring
you remove the inner cap seal from the bottom. J/E actually used the wrong seal type there. They used a "U-cup" type seal with a backup ring. The open end of "U" faces downwards. If you have the opportunity to replace the "U cup" with an o-ring or four lobed quad ring then that would be a good move. The groove is still cut too wide and you have to use the backup ring with any seal. The upper shaft seal is also the wrong type which is why these system don't last as long as others. Most trim systems go 18-23 years. This trim starts having problems as early as 12. The outer seal from factory is an oil seal design with spring loaded lip. It has a cup shape that collects oil, dirt, water, and debris. The collected debris often causes the rubber lip to fail. If you have the chance to replace the "U" shaped seal with an angular scraper type seal, then do so. An angular scraper such as a "D profile rod wiper" will last 18-20 years in this application. However, it may be almost impossible to find the right size with an encased steel ring (aka press fit). Check with the counter at local industrial hydraulic supply.
as regards actual removal:
you want to leave the existing backup ring. It's job in life is to be slightly larger than the groove and reduce the amount of o-ring slosh when the piston shaft moves. The old one will last for 50 years. The risk of damaging a backup ring during install outweighs the risk of your old one being worn. So leave the back-up ring (it looks kind of like an oily, thin, washer made from pressed plastic cardboard). Luckily, the piston shaft seal is one of the standard sized parts in that system. You can run to grainger, fastenal, or industrial seal depot and get ASA size # 208. Quad lobe (aka double sealing) buna70 would be best. Standard round buna70 would be second. ucup would be fourth or fifth.
To remove the u-cup, flip the cap over so that you are looking at bottom. Take a small jewelers screwdriver and jam it into the open side of "U-cup". Carefully pry out the old seal. If it cracks or tears make sure to get out all debris. Leave the old "bronze filled backup ring" . When installing the new seal the ideal arrangement is backup ring towards the inside and o-ring towards the outside. This is because a retracting shaft will be dry and have more friction then an extending shaft. However, if you use a u-cup then the backup ring has to go on top so that it will not interfere with the collapse and expansion of U. An oring is better since it seals in both directions. A quad lobe double seal is best since it wipes at the leading edge in both directions. You do not want to use BN90 (hard) rubber. This is a low pressure fitting. Lifespan will not be increased by the use of hard rubber but the ability to seal small scratches and dimples will be less. The end result of hard rubber is a greater risk of water intrusion.
i think that covers it. oh, wait ... while you are in there, replace the seals between gearcase and manifold, filler cap, and MRV. If you have gone to the trouble of removing tilt cap then it doesn't make sense not to spend the extra 30 minutes and do a full 100% renewal. New poppets would be awesome too. Lack of poppet seal is another design weakness in the original. If there is any water in system then go to grainger and buy a bag of 3/16" precision chrome ball bearings and replace every ball valve in the system. The MRV tip is not included with standard seal kit. you'll want to replace that. get a size 008 quad ring, square ring in BN70 material or a 008 BN90 o-ring and install it on tip of manual release valve (MRV). I like the quad ring because it seals best against a damaged aluminum seat. However, the BN90 oring is best at avoiding compression damage and will last longer if your mechanic is a wrench gorilla. Speaking of which - avoid over tightening your new MRV. Over tightening the mrv can cause the metal MRV housing to contact the aluminum manifold seat. I repair a lot of systems because the owner has overtightened the MRV and caused damage to aluminum or seal at tip of MRV.
ok .. i think that covers it ... first, longest, and last post on this system going into such detail. if you want to keep it, then bookmark it. I avoid answering same questions twice. Good luck with your rebuild. Its an easy system to fix once you have the right parts.
