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MG MGB Technical - Bonnet alignment

Aligning the bonnet (hood USA)

Anyone have any tricks for aligning the bonnet once it has been removed? I thought I scribed lines on the flanges but the thing kicks up on the left side if I use them as a guide.
John Lifsey

John - There is no easy to get the bonnet aligned that I know of, unless guide holes have been drilled in the flange. there are holed for roll pins through the hinge arms. Once you do get the alignment correct, use those holes as guides to drill the same size holes through the flange on the bonnet. This won't help you this time, but the next time you remove the bonnet, you can press roll pins through the holes, which will line the bonnet correctly before you tighten the bolts. Cheers - Dave
David DuBois

John - it was trial and error in my case, but it is possible to do the bolts just tight/loose enough to allow the bonnet to shut, carefully, and then press down to get things level, carefully open it again and tighten the bolts.

You probably do something similar, but I always use a one-foot square of foam-backed carpet on each corner of the opening in front of the screen to prevent accidents while adjusting the bolts prior to shutting.
John Bilham

Thanks John, I'll try it that way. I have a hard time in getting the bolts loose enough to move but tight enough to hold until I can snug them on down. Guess there is no "magic" trick for this one.
John Lifsey

As John B, I had the bolts just tight enough that I could move the bonnet around and lift it to fully tighten. The bolts only needed a couple of goes to get them to the right tension, and after tightening it was right first time.
PaulH Solihull

Just a silly side question, but can a hood not being set in place being perfectly even all the way around, cause the hood to pop open to safety catch?

I've been trying for 2 years to get my hood to stay down. I've replaced everything but the cable, which is fine. But then I think each of the parts (spring, bolt, etc. were fine too). Each attempt at adjusting shaft length at bolt in bonnet/hood only changes how long or in what bump in the road condition will result in the hood popping open.

When closed all the bouncing and shaking of the hood or front end, cannot get the hood to release. This morning, I was going around a gentle curve in a residential neighborhoold, and Pop - up went the hood to the safety catch.

Makes for one nervous driver, hoping the safety catch works.

I've even gone to wiring the hood down, only to have it pop loose against the not tight enough wire.

I've tried loose bolt length, and I've tried a very tight bolt length adjustment that pulls the hood down below the fender line, still it pops open.

Your thoughts.


R.W Anderson

Too tight is not good for holding the bonnet down, it seems to need to be able to move up and down as the car flexs with driving loads. I have always kept mine greased, if they become sticky they can pop open as the car bends. Again I think the 2 parts need to follow each other to work. If that doesnt help it may be that the mating parts of the catch are worn.
Stan Best

It almost sounds as if your hood is slightly deformed...Are you sure there are no high spots?
Or twists?
Close the hood , with the latch, and sight along both sides (along the edge of the hood)...If there is a high spot, it may be the cause of your problem....
Other cause, may be twist at the hinge...Make sure all gaps are the same on both ends or sides....
One more possibilty, is that the cone-nut is worn out, or the catch is worn out.
E.B. Wesson

I compared my parts to several B's on Saturday and noted that the length of my bolt/pin in hood is about the same and my spring tension at latch is the same. I also compared where the sliding latch comes into center of area when pin/bolt enters lock and this too was about the same.

The cone nut at end of bolt/pin is new.

I haven't looked for high spots in hood. But I will.

I do know the spacing at back edge and sides of hood are not perfectly equal, but I'll try to make them so.

I did see on one B this past weekend that owner had installed a second set of rubber stoppers/guides at hinge end of of hood.

For now I've wired the hood shut.

Can't wait for all the built up tension to snap a fender off instead of hood opening.


P.S. it is an aftermarket hood, and very suspectable to twisting, I'll have a look at hinges too for bends.
R.W Anderson

Only some mis-alignment or inadequate engagement of the pin and latch should allow the bonnet to pop up over a bump. This could well be because the bonnet is misaligned as well, but is just as possible if the bonnet is perfectly aligned but there is still a problem with the latch.
PaulH Solihull

My '63 Sprite did that for most of the time I have owned it. I could never get the adjustment to keep it down.
I was cleaning up the underhood shut panel and removed all the hood latch parts to clean and paint them.
I noticed under close inspection that the latch arm or the flat bar that the cable is attached too was worn away where it contacted the pin.
You could not see it when it was on the car but was clearly worn compared to another one I had.
Replaced it and now the hood always stays down.
MK Mike K

Theoretically, mechanically, if all parts are new, it should be impossible for the hood to come up, even with any flexing, since with the latch properly positioned when closed, the hole that remains is smaller than the cone.

I'm guessing you've checked that the flat back of the cone is just that, flat, and the latch similarly so? Would it be worth filing the back of the cone slightly concave around its pin?

I've just checked mine. The hole is 11/16" with the latch 'closed', the cone is 3/4", so mine relies on 1/16" to stay down. Some of the roads in this part of France, while not potholed, can be very uneven and must generate flexing, but I don't have a problem.

I'm guessing also that there are a lot of contributors to this thread (me included) that would love to be looking at your bonnet fixings right now!

Good luck

John Bilham

I will return, as I often do - to the measurement of the latch opening compared to the locking pin. I must have a lot of torque in the hood too, as I've taken wire through the hood/bonnet and made a loop. I have another stout wire going through the grill. With hood down and latched I loop the two wire loops together. It is more of a double safety approach to problem, as just the right bump still pops the hood open.

Today when going 70 mph down the expressway to work, it popped open to safety latch, defeating the wire loops.

As I do not take my heart meds until after I get to work, driving with a partially released hood in rush hour traffic is a tad unrelaxing.

Now to look at a minor adjustment to lengthen the pin a turn more to see if it makes a difference.

Always tweaking things. Never relaxing. Eventually I may bolt the hood down. Oh, and the gap around the hood is just ever so slightly off in one corner, by maybe an 1/8". I may move hood too.
R.W Anderson

You could try removing the rear seal from the lip and the radiator diafram one to see if that makes a difference. One of them may be flexing your bonnet to make it open.
Worth a try.
Ste Brown

Well I went measuring things last evening. Surprised to be able to confirm John Bilham's comment about there only being 1/16th of an inch difference between the 3/4" cone diameter on the pin/bolt and the 11/16" opening in the latch. That is exactly what mine "WAS".

I'm surprised more hoods don't pop open.

I removed the entire latch. Cleaned everything, and then noticed the underside latch component area through which the arm moves to open and close the latch.

I got to thinking (which is dangerous for anyone or anything to be within 100' feet of) and thought if the restriction to having more than 1/16ths difference is the opening in the underside latch assembly, why not lengthen the area to let the arm go further, thus letting the locking mechanism come closer to center, thus creating more surface area holding the pin down.

So I made the whole 1/16" longer, creating an 1/8" overlap. Put everything back together, measured things again, and felt I'd accomplished something.

This proved not to be the case, once I test drove over a rough road, and hood popped open to safety latch.

What is additionall bizarre is that the hood closes so nicely, smoothly and secure. No manner of bouncing, twisting, jerking of the hood can get it to release while parked.

Wanting to drive with a decreased blood pressure level, never knowing when the hood will pop to safety catch and never knowing if the safety catch would come loose; I purchased cables, clamps and spring loaded clips.

I secured a 6" long metal cable loop in hood and another through the grill, (through existing holes) so that when the hood is closed the two loops almost touch each other at the center of the hood/grill.

I then use two short spring loaded metal clips to secure the two loops together. Trial and error will determine how much to shorten the two loops to make the clips-wire loops tighter.

Don't try this at home. This is not proved to be a solution yet. But my blood pressure should go down a tad.

R.W Anderson

0.68" i.e. pretty-much 11/16" and 3/4" is what mine has as well, so I don't think the 1/16" overlap is the issue. Maybe your latch spring, or even the pin spring, aren't strong enough, the former allowing the bonnet to jounce down then shock the latch open when it comes back up. My latch spring takes 21 lb on my spring-balance (with a screwdriver down through the latch and held upright) to start moving it, and the pin spring takes about the same to start moving just one side of it. Try putting polystyrene blocks round the pin to make it harder to push the bonnet down to latch it (be careful where you push) and see what difference that makes. 499,999 MGBs can't be wrong needing all these mods, there must be something wrong with yours.
PaulH Solihull

I had a 64 MGB back in 1975. I was going 65 MPH, at night, when the hood flew open. Fortunately I had the top up. All of a sudden everything went black. Took me a second to realize what happened. I pulled to the side of the road and saw the hood was bent over the top frame. I bent it back and the hood latched shut and I drove home. I immediately installed "hood pins" so the hood never had a chance of coming open by itself. To this day I do not know why the hood flew open, or why the safety latch didn't catch. I now have owned a 76 MGB for 16 years and although I have never had a problem with it, every time I drive it with the top down I worry about the hood opening. I have never fiddled with the latching mechanism as I don't want to "disturb" it. I have been considering installing cables so if the hood did pop open at least it couldn't come over the wind screen.
P Ronning

This thread was discussed between 06/08/2011 and 28/08/2011

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