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August 18, 2021

Rocker Cover-Bonnet Interference

I really like those aftermarket finned, cast aluminum rocker covers for these cars.  Compared to the stock pressed sheet metal covers, they seem to lend an air of--I don't know--gravitas, I guess.  It's now hard for me to imagine my TR6 without it.

So I bought one for the GT6.  I'm pretty sure it's exactly the same part.  I buy the covers in bare metal because they are a little cheaper, and paint them myself.




As I was preparing the cover to mount to the engine, I made a mental note to check the bonnet clearance before closing it the first time.  What prompted this is that I know that the GT6 bonnet's "power bulge" is there for a reason, and that even so, the stock clearances are close.  Add to this that the new cover is at least a half an inch taller than the stock cover.




So, when it came time to install the bonnet for the first time with the rebuilt engine in place, I was careful.  I adjusted the bonnet hinge attachment so that the bonnet was as high as possible, and carefully lowered it to its home position without incident.  Then, crawling part way under the front end, I tried to check the clearance between the rocker cover and the bonnet underside.  Well, there wasn't any clearance.  The bonnet was touching the cover right at the forward end of the leftmost fin.  (This is because, I know now, the rocker cover is not centered in the power bulge, but is an inch or so to the left.  Think about it, and you'll realize why.)

I also checked the panel gaps I so carefully set a few weeks before.  The gap between the bonnet ant the front sill was now way too wide.  The bonnet needed to come down at least half an inch at the rear.

I, of course, am not the first one to face this situation.  Though some people claim to use this rocker cover without problems, plenty of others have seen the problem I was seeing.

I weighed the options.  Go back to the stock cover?  Well, I could, but that would be admitting defeat.  Could I lower the engine?  Not really.  The sump has a cutout to clear the steering rack under it, and that clearance was already pretty small.  Use a thinner cover gasket?  Yes, that would help, but wouldn't be enough.

In the end, I decided to resort to what some others have resorted to--shaving off the front of the rocker cover.

I did some measurements of the angle between the rocker cover and the bonnet in the area of the interference. The bonnet was sloping down at almost six degrees at that point, while the engine was tilted back by about four and a half.




I figured an angle of about 10.3 degrees would make the top of the valve cover roughly parallel to the bonnet surface in that area.  At this point, I still could have turned back.




A few minutes later, I was sort of committed.




This was only about half the amount of metal I'd have to remove, but I cleaned up the rough edge, and did a sanity check to make sure I wasn't going to get into trouble with the front rocker fouling the lowered roof.  It looked like I had plenty of room.




This was about as far as I could go without getting into the front fastener hole.




Rotating the engine so the number one valve was fully open, and putting a straight edge across the opening showed that the clearance was still fine.




I cut a piece of 0.075" aluminum to close up the hole, and blasted the cover clean in preparation for welding.




About the welding.  I'm a self taught hack MIG weldor on steel.  Aluminum is way different from steel, though.  I've done one MIG welding job on aluminum using a spool gun, and I considered the whole process a barely controlled disaster.  Aluminum sheds heat so quickly that the machine has to be set to very high amperage, and high wire speed.  This means that the weld travel is way faster than I was comfortable with.  The rocker cover material less than 1/8" thick, and the cover plate was less.  I worried about burning through the thin sections.

On the other hand, I've always wanted to try TIG welding, and always thought that if I came upon a job that really needed to be TIGed, I'd buy a TIG machine.  Well, I thought this was that job, so I bought a TIG machine and started to practice.  And watch Youtube videos.  And practice some more.  After a couple of days of practice and videos, I could occasionally make good TIG beads in aluminum, but mostly not.  A couple more days, and I was still nowhere near confident enough in my skill to move to something I could easily ruin.




I got frustrated and impatient.  This was taking too long.  In the end, I revisited the MIG.  I practiced, and the progress was faster than the TIG.  I figured out a couple of tricks that helped.  I'm sill not a good aluminum MIG weldor, but I came to the point where I thought I could fake my way through this job.




Setup, tack, and let 'er rip!




Luckily, the welds do clean up.




I discovered this little crack during the process.  This cover has never been in service, and never been dropped while in my possession, so I think it came this way.  With my newfound confidence, I fixed it.




I also realized during this process that the front cover fastener also had a very tight clearance.  Neither the fasteners that came with the cover, nor the trick ones I bought would work.  I made these little low profile thumb fasteners.  I'm not sure if I'll be able to torque these sufficiently by hand, so they might not be the final answer.




Repainted the reshaped cover.  I first tried to use a high temp "wrinkle paint", but couldn't get the wrinkle to be consistent.  So I stripped it off and used a textured "truck bed" paint.  It looks great, but is only rated to abut 200 degrees F.  On the other hand, I've had it on my TR6 for a couple of years, and it's held up fine.




Aesthetically, to me, that broad flat space at the front of the cover just begs for something.  I don't know what, but I played around with a couple of 3D printed badges.  These aren't it, but I'll keep looking.




On the engine.  Bonnet adjusted as low as it will go at the hinges, and I have a scant 1/8" clearance.  Mission accomplished.




This was sort of a harrowing project.  And it took way too long.  Cost was almost zero (except for the TIG welder, that is).

Comments to Ed at elhollin1@yahoo.com

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