Mk2 Trunk Lid cracks

Cracks have appeared in the ABS trunk at the backrest mounting location. I've planned to repair/reinforce with a 6"x8" aircraft aluminum plate pop riveted externaly to both the metal trim piece and ABS trunk wall, then remount the backrest thru the plate. Stress forces are now focused on the reinforcing plate, and difused before transfer to the ABS. This plate will be concealed by the passanger backrest, and only the pop rivets will be visible inside the trunk. Maybe I should use thru bolts with fender washers in the ABS instead of pop rivets........

ideas/input/critique?

-Pete, in Tacoma WA USA

if you could shape the metal to the trunk contour, you could use an adheasive to attach it

Here is an article Rick Butler wrote for the Venture Touring Society's monthly magazine Venture Road:

When I first heard of trunks cracking behind the rider's backrest (probably sometime in 1988), my first thought was it was probably caused by the weight of larger riders. Now don't get offended girls, because I discovered I was wrong when I disassembled my '86 Royale getting it ready to paint (after a couple of years and 30,000 miles). I was appalled as my trunk was cracked up pretty good also. Now my wife Linda only weighs 100 lbs, so I knew it wasn't caused from abuse.

I started to really study the cracks and what appeared to cause the problem. My first observation was that the cracks were covered up by the mirror, so I never would have known I had a problem until it was probably too late. Nina, I noted that the butt welds of the aluminum trim were cracked on both the top and bottom of the trunk. This caused a misalignment of the sealing points and popping sound when the trunk was closed. When I observed how the backrest was mounted to the trunk, I found a 1" by 6" mounting point with 2 studs from the backrest and the same size strap on the opposite side where the nuts were placed, also under the mirror. I immediately realized this was not a large enough mounting surface to support the pressure received from this point that is located right at the lower lumbar of the rider's back. It allowed gradual flexing which caused the crack in the weld that joined the ends of the aluminum trim. Once this weld broke, it allowed more flexing to occur which let the plastic crack and spread further.

I realized what was needed was a reinforcement plate to cover this mounting point, large enough to stop any possible flexing and one that should be located on the outside of the trunk. A key factor was that this plate should extend coverage over the aluminum trim and it would be best to attach to it to provide the maximum strength possible. Just placing a fiberglass patch on each side would be short- lived and it would end up cracking again. I ended up at my favorite hardware store trying to decide on the material to use and ended up with an aluminum kick plate which I cut to 4" X 8" and bent it to fit the contour of the trunk surface. The plate wasn't as heavy as I wanted, but I figured it would do as it wouldn't rust and wouldn't need painting. To attach it to the aluminum trim, I drilled halfway through the rail and into the slot that contained the rubber seal. Four short sheet metal screws worked perfectly and, when finished, resulted in a solid area that resisted any possible flexing.

Once I installed this plate and mounted the backrest, I left it undisturbed for over a year and another 23,000 miles (mostly with my trusted passenger). It was unfortunate that I had to repaint the bike, but it gave me a chance to observe how the plate had performed. Since my original cracks were pretty long, I had put a single layer fiberglass patch on each side. Upon removing the plate, no further cracks or stress points were found. Now it was also about this time that Dave Henderson and I were returning from our 1st V-Daze at Taos, New Mexico, after forming up Tri-Star Industries. We were looking to enhance our product line and this plate surely seemed to resolve a problem that all '86 through '89 Venture riders with passengers would face at some point in time.

When we decided to produce these plates, we chose to use a heavier gauge aluminum than my original test model. We also had to start with a 4' X 8' sheet of aluminum which yielded over 140 plates. Well, we sold these plates in a couple of years and now are on our second set. And we've heard some real interesting stories. I think the best one was one Dave and I experienced at the '91 V-Daze in St. Ste. Marie, Michigan. One couple carefully looked over the plate we had on our demo bike and listened to Dave describe how the problem started and how the plate resolved the situation. The husband thanked him, but stated that they didn't have a problem with their backrest or trunk. It wasn't 5 minutes later that they were back, with the wife chuckling at her husband who had a sheepish look on his face. They had left the show and when the wife went to get on the bike, the backrest (which she used as support when getting on) came off in her hand. The trunk was completely busted out where the backrest mounted to the trunk. Yes, they purchased one of our plates. I advised them to see about getting the trunk replaced under warranty.

Fortunately Yamaha has been great about replacing trunks that have cracked or busted out from the backrest. However, it works best to have a dealer that will support your claim but sometimes you have to get pushy to get them to turn it in. I have lost count of the calls we have received for plates from riders that have gotten a new trunk from Yamaha, who want to stop the problem from happening again. I have determined from viewing trunks at shows and from talking to customers that it is not a matter of whether the trunk will crack from the backrest mounting as to when it will crack.

For those folks with a 1990 or later model, Yamaha has revised the mounting surface to extend to the top bolts in the mirror which appears to resolve the problem. This is a rather expensive piece and I guess they decided not to retrofit '86 - '89 models with the update but to replace entire trunks instead. I say this with tongue in cheek as Yamaha has done sillier things in respect to warranties.

The main reason I wrote this article was to let everyone that we had not already reached through our ads and word of mouth know about the problem looming behind the trunk mirror of '86 through '89 models. Dave and I are members of Texas Chapter 6, a pretty large chapter and most all of our Ventures are fitted with one of our backrest plates, many of which were installed during one of our many chapter work days (where we get together and work on each others bikes). It was my thought that we could make other chapters or groups a special deal on multiple orders to help resolve this evident problem of cracking trunks.

Each plate kit contains mounting screws, a drill bit painted to form a depth gauge and detailed instructions.

Rick Butler #00007

are these plates still available? is anyone producing anything like it?

We may have to contact Rick to see if we can put together a group buy to get him to make some more.

Mine is not cracked yet, but I know it is just a matter of time. Especially since that is the point that takes most of the force when I have to push the bike backwards.

The following is courtesy of Neil McRobbie:

The backrest mount over stresses the lid on the 1st gen....I installed a reinforcement plate that Rick Butler (Tri Star Industries) sold years ago. It’s sandwiched between the backrest and the front of the trunk, and screwed to the aluminum trim at the bottom of the lid, to stiffen the front of the trunk.

You still would want to fix the plastic and then consider installing a plate.

First pic shows installed plate...screws visible into aluminum trim.

Second pic is a spare plate I had laid inside the trunk lid to show area covered.....on the plate...top holes are for Royale vanity mirror (mine is a standard, not used), middle holes are for the backrest studs and lower row is for the 4 screws for the trim. There’s a slight bend to the plate to fit tight to the trim and the trunk front face.

This also bridges the very common broken weld on the trim center joint.

Thanks for all the input............ I'm on the right track.

I may glue the plate to the ABS trunk wall, and rather than pop rivet, use sheet metal screws into the aluminum trim.

Got my generic aluminum plate 4"x10"x1/8" at local ACE Hdwe $5.00.

-Pete, in Tacoma WA USA

I once bought a trunk off Fleabay with a metal plate like you are thinking about...