Author: mike2209

Retired Chartered Mechanical Engineer and Fellow of the Institution of Mechanical Engineers. Aston Martin DB9 enthusiast and owner.

Aston Martin DB9 – Sheared Bolt Repair

On By mike2209In How To4 Comments

Every now and then you will come across an existing sheared bolt or you will shear one yourself, either way they have to be repaired. Sometimes (rarely) there might be a length of bolt or stud proud enough to be able to get a grip of it with mole grips or self tightening pipe wrench. If you try to get a stud out this way be sure to soak it thoroughly with a good penetrating oil for as long as you can first and work the bolt backwards and forwards to loosen it don’t try to undo it in one direction straight away you have to “persuade” it out.

The sheared bolt on my Aston’s slam panel was where it bolts to the bonnet release catch. The shear is about 3mm below the top of the steel of the catch and is quite a common failure. It’s quite easy to over tighten and shear smaller sized bolts particularly when using ratchets or spanners with handles/lengths that are up to 200-250mm (8-10″) long. One trick is to hold the spanner in the middle of its length to reduce the lever arm if tightening up smaller bolts. On more critical bolts use a torque wrench, most torque figures are given in manuals so use them. The overriding requirement is common sense, are you bolting up a bit of light weight “slam panel” as in the case above or a major suspension part !!!

The worse situation is the sheared stud or bolt that shears below the surface of the steel and it’s the most common. There is a reason why car manufacturers say you should use new bolts in critical areas and it’s not just to make money out of us. Bolts that are located in areas of high stress, high temperatures or exposed to potentially rusty locations will experience changes to their mechanical properties over time. Corrosion can reduce the surface condition of bolts not to mention the “eating away” and “pitting” of the threaded area. The pitting can eat into the steel causing areas of potential weakness that will fail under the load of tightening. Bolts that are exposed to the effects of heat (heating up then cooling down) such as engine/cylinder head bolts or exhaust bolts and that are under load for a long period will not exhibit the same mechanical properties once removed and then reused. Hence manufacturers recommend replacing all the cylinder head bolts once they have been removed which often seems a little extravagant as they always look fine but as I’ve explained it’s not done without good reason.

There are two options to repair a sheared bolt. If possible it may be extracted by drilling a hole down through the centre of the bolt and using a stud extractor. These extractors are readily available but I have to say I haven’t had much success with them. The extractors have a left hand thread so as they are screwed into a drilled hole in the sheared bolt or stud they tighten in the direction that will unscrew the sheared bolt.

Stud Extractors

I always try to extract a bolt but usually end up drilling it out and re-tapping the hole. The size of the sheared bolt or stud determines the size of the hole to be drilled and tapped here are some common drilling sizes for tapped holes that you might come across when working on your Aston.

As you will see there are a number of different Pitches for “Fine” bolts so it is important to select the correct drilling size particularly if you are having to drill out a cylinder head bolt for example, you only get one chance at it. To ensure you are using the correct size drill you can measure the size of the replacement bolt you are going to fit using a thread gauge.

Available in the UK from as little as £5.00

When you drill out the sheared bolt consider where the swarf (waste) will fall. If there are critical items around such as say the alternator it will not react nicely to having small metal pieces dropped into it so protect vulnerable areas with cloth covers etc..

Swarf from drilling the hole ready for tapping

If the swarf can be easily vacuumed up then covering everything up is not an issue.

Once the old bolt has been drilled out you can now start to tap a new thread for your replacement bolt. When tapping out a hole it is important not to try to rush the job by driving the tap down into the hole. You will almost certainly shear the tap in the hole then you really do have a problem as the tap is made of extremely hard steel that you will find impossible to drill out. Since taps are made from particularly hard steel that brings with it an inherent brittleness so don’t go mad trying to cut the new thread in one go.

The technique is to apply downward pressure to get the tap started whilst turning the tap half a rotation (180deg) clockwise then reversing the tap direction for a quarter of a turn (90deg). This is repeated for the whole of the tapping process until the full depth of the hole has been tapped. The small rotation backwards allows cut material to release into the grooves of the tap so that the tap does not bind in the hole and potentially break. Once the tap has cut a thread of a few millimetres you will no longer require to apply downward pressure as the tap will use the thread it as cut to provide the downward force into the hole. During the cutting you should use a light oil or grease to aid the cutting process, WD40 is a good lubricant for this. It is also advisable to remove the tap completely periodically to clean away swarf.

Use a lubricant and stop periodically to remove swarf

The key is to take your time, you’re not on the production line at Ford, if you are doing this job it’s probably a one off, so there’s no need to rush.

Check the bolt in the new tapped hole when finished

When you have finished tapping the hole and have cleared away all the swarf check that the replacement bolt will run down nicely into the new tapped hole. You don’t want to get into the assembly of everything to find for some reason the replacement bolt you are going to use is too tight or too slack in the hole.

Remember the key is take your time and start off by marking the centre of the broken bolt with a good centre punch mark so your drill will not wander off the centre of the bolt and drill squarely down the bolt. You don’t have to drill out the hole to the final tapping size in one go, it’s often better to drill out in say up to three stages to arrive at the final size. If you follow these instructions you should be able to replace a sheared bolt on your Aston with no problem.

There is a short video here showing the drilling out and tapping of the sheared bolt on my Aston’s bonnet catch.

Mike (Aston 2209)

Third Hand for Undertray Removal and Installation

On By mike2209In AdviceLeave a comment

When you’re working under the Aston just about every job seems to require you to remove the undertray or underpan. This is a large sheet of Aluminium approximately 1500mm long x 800mm wide. In itself it’s not heavy but due to its size it is very cumbersome to handle.

Undertrays

As those who have removed the undertray will know you seem to be undoing bolts for ages (about 36 in total, I kid you not !!!)  before you can get it down/out. If you are doing an oil change there is a hole directly below the engine drain plug but I would defy anyone to get that plug out without the oil running all over the undertray. I don’t see the point of the hole as you have to remove the undertray to change the oil filter anyway, unless you do it from the top as Steve has done finding it almost impossible to remove the filter from below on a LHD Aston.  I can confirm that on a RHD Aston it is relatively easy to change the oil filter from below.

Undertray hanging vertically under the Aston

When I first started removing and replacing the undertray I had to get my wife to hold the back end whilst I removed the final bolts then we could lower it together to the floor. Since just about every job under the car requires this taking off I decided I had to come up with another way of doing it and hence the “Third Hand” was created. When I stopped to think about it the answer was simple in the end … the best ideas are always the simplest.

Hook the string over exhaust bolts
Pieces of wood pass through air flow fins

The “Third Hand” couldn’t be simpler, a piece of strong nylon string and two pieces wood. As you lift up the front end of the undertray the rear hangs from the exhaust bolts allowing you to feed the front end of the undertray over the lip of the front valance and insert bolts to secure it in place.

With the undertray bolted in position at the front the next stage is to insert the central bolt through to the main cross-member. Once this is in place the “Third Hand” can be removed and the rest of the bolts fitted.

Here is a short video showing how this works in practice.

Mike (Aston 2209)

Air Conditioning Investigations

On By mike2209In Advice5 Comments

So, we decided to go out for a short trip now that the Coronavirus lockdown has been eased a little and it was a beautiful sunny day. We set off with no particular destination in mind just a ride out for a change of scenery, we don’t think it is fair yet to descend on the local beauty spots where people who live there have also been in lockdown.

As I said it was a nice sunny day with temperatures in the low 20’s C so on went the Air Conditioning. Having travelled about 15-20 miles we both said “it’s a bit warm in here” and on checking, the Aircon wasn’t working. We decided to return and came back with the windows down !!!

I have quite a good setup in the garage with just about any tool I might need for doing a job as some of you might have seen in my previous Blogs, what I don’t have however is Aircon testing and gassing equipment, who does !!!

Anyway, I jumped on the internet to find a mobile guy near us to come and do a few checks. As it happens my wife’s Audi had a problem as well so I thought we could kill two birds with one stone. The first guy I rang asked me what the cars were, I told him an Audi A6  S-line 3.0ltr TFSI and the second car an Aston Martin DB9. There was then a pregnant pause and I could imagine the money signs in his eyes🤑! He came back with “I could do them both for only £465.00”. After a deep gulp I said I’d get back to him if I was interested but at that price I said, I think I’ll just be opening the windows !!!

My next call was to “Car Aircon Services” http://carairconservices.co.uk/ and I spoke with Damian. He covers Manchester and North Cheshire. All his prices were set out on his website, no hidden extras, he told me when he could come and even arrived an hour early. As soon as he started to look at the cars, I thought this guy knows what he’s doing. You just get that soft and squeezy feel about it. The Audi was resolved within a few minutes of checking gas pressures and connecting up his ODBII reader, a faulty pressure switch, for which he carried OEM parts in his van.

So, to the Aston, this is a story of woe I’m afraid at the moment. A check revealed no gas in the system. Moreover, we discussed the background to the car and we (well Damien) came to the conclusion as you will read.

Arrangement of Air Conditioning System DB9

Drive belt arrangement for A/C compressor drive and other items

I bought the car just over three years ago from a dealer in Wimbledon, South London and he undertook to carry out an oil change service prior to me collecting it a week later. Part way through the week I received a call saying that the air conditioning had stopped working and they would need another week to get it sorted. No problem I thought better to be sorted now than have a problem later.

When I collected the Aston, everything was perfect and as we drove back up to Manchester (about 31/2 hours just over 220 miles from the dealership for those who are not aware) the Aircon was working fine. However about 3 months later the aircon stopped working so I gave the dealer a ring and he said bring the car back and he would get it sorted again. After some discussion about the distance involved and me having to make two return trips to London and associated costs, he agreed for me to get it tested locally. I found a local mobile guy (not Damien at the time) who came and checked it out but he concluded that there were leaks from both the condenser radiator and the compressor. I relayed this to the dealer who was quite sceptical at first when I told him it needed a new condenser radiator and a compressor plus fitting of same. Eventually he agreed as long as he could supply the parts and my guy could fit them. A few days later an OEM condenser radiator arrived at the house direct from Aston followed by a “reconditioned” compressor from another company. These were duly fitted by the guy I was using at the time and the system re-gassed.  

Aston Martin DB9 – Refrigeration System

All was then OK for the next 21/2 years or so, until now. Damien found traces of dye under Ultra Violet on the connections to the new condenser radiator but he concluded that this was dried residue from when the condenser was fitted. More serious he found evidence of fresh dye around the pulley drive end of the compressor. Damien suggested that even though the compressor was a reconditioned unit it should last a good number of years certainly more than 2-3 years.

Damien put forward a hypothesis with which I am inclined to agree. He has seen it before that a leaking system is repaired with a sealant additive. This works in the short term, however it is only a temporary repair, moreover it can lead to more problems. It is possible that the dealer in London might have had the original leak repaired by the use of such an additive. It follows that this repair would then fail after a short time, perhaps shorter than he would have expected and he then had to provide new replacement items under the 6 month warranty.

Unfortunately, once the sealant is in the system it is near impossible to remove, it requires complete flushing and possible replacement of other parts of the system. The sealant can blind pipes and galleries along with the other items in the system such as the expansion valve, receiver drier or the accumulator this causes the compressor to run at higher pressures to maintain circulation ultimately this higher pressure weakens seals in the compressor and produces the leakage trace usually at its drive/pulley end.

Expansion Valve comparison with sealant contamination
Damaged compressor shaft seal with sealant present

For now, we are in the testing period as Damien has refilled the system with gas at my request and we will see how long the Air Con keeps working. The result will determine the path forward but now the leak is established I suspect it will not be long before I have another Blog to post on changing the Air Con compressor or even more items !!!

A quick search on the internet found quite a few of these products on the market all professing to seal your system leaks, but none advise of the potential pitfalls. I found an article on line that confirms everything that Damien told me, you can read it by copying and pasting the link, if it doesn’t work don’t ask me what do I know, I found through Google so good luck !!!                                            http://www.ricksfreeautorepairservice.com/does-ac-stop-leak-sealer-work/

There is a short video of the preparations for the investigations and some commentary on the results. See    https://youtu.be/e6nYb2IMbQE

My recommendation would be to bite the bullet on your air conditioning and get someone in like Damien who knows what they are doing and don’t go for short term fixes, it could end up costing you a lot more in the long term. Watch this space over the next few months (or perhaps days !!!) for progress updates.

By the way Damien’s price for both cars one with a new pressure switch and the DB9 checked out and regassed not to mention his advice (he was here for over 2 hours) was £134.00, more than reasonable.

Mike (Aston 2209)

Rear Subframe Surface Rust Descaling in an Aston Martin DB9

On By mike2209In Advice, How ToLeave a comment

Some of you may have seen one of my (@aston2209) previous Blog on changing the rear lower wishbone assembly and at the time I commented on the condition of the rear subframe. It had quite a lot of flaky surface rust that was both unsightly and could lead to more aggressive corrosion in later life for Aston 2209. At the time I wanted to undertake cleaning up the subframe but since it was in the winter and there was a lot of damp atmosphere from day to day, I decided to leave it until the summer. However here we are in May and we have just gone through a really long period of dry weather with warm temperatures and seeing as we are also in “lockdown” due to the Coronavirus it seemed like a good time to do the job. Continue reading “Rear Subframe Surface Rust Descaling in an Aston Martin DB9” →

Don’t slam your DB9’s Bootie – Changing the Boot Lid Gas Strut on an Aston Martin DB9

On By mike2209In Uncategorized10 Comments

Ever since I bought Aston 2209 the boot has effectively closed under free fall. We have of course learnt to be careful with it, but after a couple of frighteners where we have dropped it and it has slammed shut I decided for the small amount of money involved it was crazy not to resolve the problem. The potential for breaking the rear glass really exists. The boot lid is supported on gas struts that are part of the hinge assembly but once the gas has started to leak away they loose their effectiveness. Even when you have removed an old gas strut you will find it very hard to depress so you might think there is nothing wrong with it. Unfortunately there is, so bite the bullet and buy a couple of new ones. Continue reading “Don’t slam your DB9’s Bootie – Changing the Boot Lid Gas Strut on an Aston Martin DB9” →

Loud knock from the rear – on acceleration and braking

On By mike2209In Uncategorized12 Comments

So, either it was a coincidence or something to be remembered in the future. Just before Christmas I washed Aston 2209 and put it in the garage where it stayed for nearly 3 weeks over the Christmas / New Year period. In the New Year we decided to go to Anglesey for a day trip and a walk along Newborough Beach to Llanddwyn Island followed by an early evening dinner at The Oyster Catcher in Rhosneigr.

Newborough Beach to Llanddwyn Island
The Oyster Catcher in Rhosneigr

I got in the Aston and selected “R” and didn’t move …… strange I thought, so I gave it a little more right foot and with a loud bang/crack we were moving. I put it down to the brake pads and discs/rotors being stuck and thought no more about it. I guessed that the wheels having just been washed and rinsed off meant that there would still be water between the pads and the discs/rotors. As you will have probably seen when you leave a car for a few days following rain or washing a light rust discolouration can take place on the surface of the discs/rotors which disappears as soon as you start driving. Aston 2209 had been put away with wet discs/rotors and stood for about 3 weeks so I suspect that there was a bond created between the pads and the discs/rotors.

So off we went on our day out but it was soon apparent that something wasn’t quite right. As we pulled out onto the main road there was quite a loud knock that sounded like something banging against the underbody of the car. You start to think of all the worst-case scenarios …. Is it gearbox? Is it the differential? What is it?.  I drove on carefully with no other noises and in fact kicked the Aston down and accelerated along the country lane and nothing, no noise at all. I then had to stop when a set of traffic lights further along the road changed to red, as I started to brake we heard the knock again. When we set off again “knock” ….. I was now convinced that we most probably had a bush that had worn and quickly found that as long as I didn’t accelerate hard from rest or brake hard the Aston drove perfectly so we continued on and had a fantastic day.

A few days later I got Aston 2209 up on the lift/ramps to see what the problem was. Out came a couple of levers to start levering all the ball joints and bushes on both sides of the rear end with a bias towards the LHS as that was where the sound seemed to be coming from. I missed the offending bush the first time around and wrongly came to the conclusion that it must be something else.

I have been wanting to change the differential oil for a while and as I had everything already bought and available I thought I would do it now to rule out any damage that might be evident in the differential. My thinking was that if the knock was coming from the differential then when I dropped the oil there might be some metal bits on the magnetic drain plug. After the oil had fully drained I checked the filter which was relatively clean and there was no evidence of anything metallic on the drain plug.

A warning when undoing the filling plug
take care you don’t do as I did and damage
the oil cooler fins as the filling plug comes
loose. I had the socket on a breaker bar and
the filler plug being quite tight caused me to
swing the breaker bar into the cooling fins,
fortunately no real damage done.		This image has an empty alt attribute; its file name is 20200115_135316-2.jpg

On the second pass of playing with the levers I found the offending bush. What I found was not actually a damaged bush but in fact a fractured outer bush mounting in the lower wish bone suspension arm on the LHS. The bottom outer bush mounting in the arm was completely cracked across its width as you can see in the photo indicated by the arrow.  

The 3D drawing extracted from my workshop manual shows a good view of the rear subframe and the various suspension item locations. I have highlighted the Lower Wishbone.

Once the mounting bolts had been removed from the lower wishbone it was a simple manoeuvre to lever it downwards and out.

With the wishbone out it was easier to see the extent of the fracture that extended the full width of the bush mounting area.

The bush is an interference press fit into the wishbone arm at the outer end where the wheel hub mounts. Having been cracked the required interference fit is compromised and the bush is able to move backwards and forwards when mounted in the car and as it moves from one extent of travel to the other it “knocks” against the body of the wheel hub. The bush was very easily tap out.

NEW and OLD

The new wishbone comes complete with factory pressed fit bushes already in place. Installation of the new wishbone arm is a direct reversal of the removal sequence however there is one aspect that must be adhered to. Rubber bushes have a predetermined operating range from the as installed position. Bushes are not a rotating joint, the bush is designed to allow say a defection / part rotation of  +/- 10-20 deg dependant on the characteristics of the rubber and the application.

Aston require that on assembly none of the bolts are torqued up until the ride height is set and to do this requires movement of the suspension to simulate the weight of the car + passengers + Fuel + luggage.

Ride height measurements
How do we do this? In my case I
have the advantage of a car lift so
what I can do is lower the car so
that the disc/hub rests on wooden
blocks on the floor thus
compressing the suspension as
though the wheel was on the
ground		This image has an empty alt attribute; its file name is 2020-03-03_22-09-11-1.jpg

If you don’t have the benefit of a car lift and you are on axle stands you can use a jack from the floor under the disc/rotor but take care that the disc does not rotate. Apply the handbrake particularly is your Aston is a manual drive as you will not have the benefit of the gearbox being locked in park.

So the car has to be lowered onto my wooden blocks until we reach a normal ride height at a hub centre to underside of rear bodywork dimension of between say 360 – 390mm, but these dimensions are based on the following according to my manual.

“2 x 68kg people in the car + 14kg luggage in the boot (trunk) + a full tank of fuel” ….. really !!!!

I’d better start bringing people in off the street and weighing them as I weigh about 85kg so that would give an uneven weight distribution, besides I can’t be in the car and torqueing up the bolts at the same time and I’ve got less than half a tank of fuel in anyway !!!!!!!!!!

Since the height is to be set without being fully loaded I decided that if the dimension was a little higher than the target 276.5mm then it wouldn’t matter too much as there is quite a wide tolerance of +/- 15mm. This dimension is only to set a neutral position for the rubber bushes so they are in their optimum position for least stress during normal running.

With the lower wishbone bolts in place (snug) but not torqued up the bushes will rotate on the bolts to the correct neutral position as the Aston compresses the suspension to the correct ride height as it sits down on the wooden blocks. With the lower wishbone positioned to the ride height the fixing bolts can then be torqued up. If you simply torque up the bolts with the wishbone in the lower position you are effectively fixing the bushes in a very low position. When the rubber of the bush in the wishbone rotates as the car sits down on the suspension it may, as a result, already be at the end of its working limit with just the weight of the car. The reality is that as we drive the bush has to accommodate +/- movements from the norm and if the bush is already at its extreme position it will then be over stressed and lead to premature failure due to the rubber failing.

With everything back together and checked all that remains is to refit the inner wing liner. As it’s still winter and damp, I have decided to defer the surface rust treatment of the subframe until the summer when everything will be a lot drier and more conducive to doing a good job and getting a good result.

Even though I removed the inner wing liner you could do this job leaving it in place. Unfortunately at the time I didn’t know that the nut for the front inner wishbone was captive as it was hidden behind the inner liner. You now know so you can remove the bolt without having to get a spanner on the nut.

A video of the search for the problem is below and includes the steps to do the repair. If you ever have this problem don’t be afraid to handle it yourself as it’s quite straight forward.

See https://youtu.be/6t6ZiGIhhSo

Mike (Aston 2209)

**********************For additional interest **********************

I have cut out a section of the Fracture to photograph for analysis by anyone who has the knowledge to do so, feel free to leave comments in the blog.

Mike (Aston 2209)

Power Window Not Working in an Aston Martin DB9

On By mike2209In Advice, How To15 Comments

The drivers side power windows stopped working in my DB9.  This is the second time this problem has happened and both times I now realise it has been due to the battery being allowed to run flat. The first time followed a period of 3 weeks where I didn’t drive the Aston and this latest time being when I forgot to disconnect my dashcams. Continue reading “Power Window Not Working in an Aston Martin DB9” →

Winter Preparation – Windscreen Washer Fluid in your Aston Martin DB9

On By mike2209In Advice, How ToLeave a comment

Following on from Steve’s article on “Storing your Aston Martin” I have just been preparing Aston2209 (my DB9) for the winter and as we enter this period those of us who live in parts of the World where the temperature will surely drop below freezing its time to check all our Aston fluids are fit for purpose.

This article concerns the windscreen (windshield) washing system something that is often forgotten until we try to use it and find its frozen solid. What needs to be done, if like Aston 2209 you have a Summer formula wash installed, is that this has to be removed and a low temperature wash water installed. Continue reading “Winter Preparation – Windscreen Washer Fluid in your Aston Martin DB9” →