Engine Update

Back in my January 2020 update post, I dropped some hints about my change in engine choice.  427 cubic inch, titanium rods and, the need for a dry-sump tank...

So if you hadn't already guessed, I am now planning on installing an LS7 engine instead of the LS3.  My engine builder, Kyle, made me an offer I literally couldn't refuse.  He also persuaded me to consider dry-sumping the motor to eek out a few extra horsepowers - hence the need to try and find a location in the confines of the AK for a remote oil tank.

So the revised engine specification looks a bit like this

• LS7 Pistons - Mahle PowerPak Forged 4032 Alloy for low expansion with Grafal anti-friction skirt coating - modified wrist pins - hot washed and checked
• Mahle High-Performance Piston Rings
• Compression Ration approx 11.3:1
• Competition Cams Camshaft (guaranteed to pass IVA / MOT)
• Competition Cams reduced travel Hydraulic Lifters
• Competition Cams Rocker Trunnion Upgrade (with needle roller bearings)
• LS7 Titanium Conrods
• ARP High-Performance Big End Bolts
• Clevite H-Series Big End and Mains Bearings - 
• MLS Head Gaskets
• Double Valve Springs
• Uprated Water Pump
• New Front Damper
• LS7 Sump Pan with adaptor for -12 oil lines to remote tank
• New LS7 Intake with 42 lb per hour Injectors
• One Piece Manley Pushrods
• New Gaskets
• New Sensors
• New Oil Seals
• Fly-by-Wire Throttle Body
• Custom Corvette Front End (Power Steering Pump, Alternator, Idler and Custom Tensioner)
• Canems ECU and Wiring Loom modified to include immobiliser 
• Dyno Run and Set-up

Kyle started pulling together all the parts for the engine earlier this year but the Covid-19 pandemic caused a few delays with some of the parts coming from the States so final assembly did not begin until mid-June

LS7 Bare Aluminium Block with pressed in Steel Cylinder Liners

Cam installed and upper main bearings in place - note dowels to assist location of end caps

Forged Steel Crankshaft 2.559in dia Mains / 2.100in dia Rod Journals

Reluctor Wheel (24X) welded to Crankshaft

Pistons and Rods ready for assembly

Piston Ring Gapping

Short Block Assembly complete

Cylinder Heads - CNC Ported / 70cc Chambers - 2.205in dia Titanium Intake Valves & 1.610 in dia S/Steel Sodium Filled Exhaust Valves

Uprated Valvetrain

Fly-by-Wire Throttle Body

Sump Adaptor to connect to remote Oil Tank

Assembly almost complete - looking like an engine!

The LS7 was the largest displacement engine in the LS engine series.  It was based on the C5-R engine used in the Le Mans racing Corvettes so is purpose-built for high performance.  It found its way into a number of GM cars between 2006 and 2015 most notably the Corvette Z06.

The stock LS7 produced a respectable 505bhp at 6300rpm and 470lbft torque at 4800rpm.  Kyle built the LS7 for Apple, the AK demonstrator, which put out around 630bhp and a shade under 600lbft torque, some serious gains over stock, and I would have been happy with similar numbers from my engine.

Kyle had the engine hooked up to his dyno at the beginning of July and spent a day checking over for leaks, before a session at fast idle to run in / bed in the engine.  The plan was for Dave from Canems to come and assist with the set-up of the ECU before carrying out the power pulls proper.

On the dyno and ready to rumble...

About mid-day on the day that Kyle was hoping to do the power pulls, I got a phone call.  "Are you sitting down?" he said.  So down I sat, thinking the engine had blown up on the dyno or some other equally catastrophic scenario.  Turned out the numbers on this beast exceeded even Kyle's expectations; 659bhp at 6300rpm and 603lbft at 4900rpm! He was over the moon and so was I!

Dyno output...

...peaking at 658.6bhp and 602.9lbft torque!

Torque exceeds 500lbft from around 3000rpm!

While the engine was still on the dyno I took the opportunity to pop up to Kyle's workshop and check it out in action.  It also gave me the chance to familiarise myself with all the various connections from the ECU to the engine sensors and to get some guidance from Kyle for when I come to start up the engine myself.

The video above of the outside of the dyno room just does not convey the power of this engine - it was like a Force 8 gale blowing out of the exhaust pipes and the whole ground was shaking.  Absolutely awesome piece of kit and I would recommend Kyle without a doubt to anybody wanting to get some serious bang for their buck on the engine front.

I should be picking engine up in a couple of weeks time so I guess I'd better crack on with getting the rolling chassis completed!!

Brake Lines Part 3 - Going round the bend...pack the distress flares

With the brake/clutch pipe routing finalised and the bulkhead bracket in place, it was time to master the art of bending and flaring brake lines.

To form the brake line flares I have invested in a heavy-duty flaring tool from Car Builder Solutions.  This is a vice mounted tool with the advantage that it came with the dies and punches to form male and female flares in both 3/16" and 1/4" pipe.

Brake Flaring Kit from Car Builder Solutions

I also bought a Brake Pipe Bender from Frost Restoration.  There are many similar tools available but I liked the look of this one as it seems to fully support the pipe around the whole bend during the forming operation, avoiding any risk of kinking or crushing the pipe.  Again it also has the advantage of being suitable for 3/16" and 1/4" pipe.  More on this later...

Pipe Bending Tool

I also purchased a 25ft roll of 3/16" copper-nickel brake pipe from Car Builder Solutions and a slightly more expensive 25ft roll of 1/4" copper-nickel pipe from Frost for the clutch line (unfortunately Car Builder Solutions don't sell 1/4" line) and the following brake fittings from Automec.

I did a few test flares on a few short lengths of pipe to check the flaring operation.  I used a simple pipe cutter to cut the pipe to length.  I did actually buy one from Car Builder Solutions when I ordered some other bits but a plumbers pipe cutter from any DIY store will do the job.  

Standard Pipe Cutter

The cutter does leave a bit of a burr on the cut end of the pipe.  Again I did invest in a deburring tool from Car Builder Solutions but I have to admit to not being impressed - it does a nice job of chamfering the outside of the pipe but makes a bit of a ragged job of the inside which I ended up cleaning up with a countersink bit in a hand drill.  I reckon that better results could be achieved with a fine file and a countersink bit alone.

Pipe Deburring Tool - deburrs inside and outside of pipe in one operation

Pipe after cutting - raised burr visible

After Deburring tool - outside edge looks OK but inside looking a little ragged

After using countersink on the inner edge

With the pipe cut and prepped it is ready to be flared.  The end to be flared in placed on one side of the appropriate die block, the other half is placed on top and the pipe adjusted so that the end of the pipe is flush with the end of the die; I left the pipe protruding a bit and then used a steel rule to push it flush with the end of the die.  The die block and pipe are then clamped into the flaring machine (note that this does not have to be tightened up with any significant force - I have read reviews where people have split the die block by overtightening - hand tight and a bit seems more than sufficient).

Two halves of the 3/16" die block

The flaring operation is then either a one or two-step process depending on whether a male or female flare is required.  The first operation is always to form a male flare using the appropriate size OP1 punch on the flare tool.  I found it necessary to ease the punch forward slowly using the lever on the flaring tool to ensure that the pin goes properly into the hole in the pipe.  The lever is then pulled around until firm resistance is felt (again no need to exert Hulk-like force on it!).  This then produces an SAE male pipe flare (or a single flare, convex flare or a bubble flare depending on which terminology you want to use!).

Punch set for 3/16" flares - OP1 for single and OP2 for double flares

Pipe installed in die block and clamped into flaring tool - punch positioned to create a single flare (OP1)

Completed Male SAE Single Flare

For an SAE female flare (or a double flare) the operation is then repeated using the OP2 punch and without removing the pipe from the die.  Again I went slowly to start and guided the pin into the centre of the hole before operating the lever again to the point of firm resistance.  After a few practice attempts, I managed to produce some very neat and consistent flares.

Completed SAE Female / Double Flare

BRAKE PIPE TOP TIP 1 - When flaring brake pipes make sure that you slide the requisite brake fittings on to the pipe before you flare both ends.  Brake fittings do not pass over the flared ends - go on, ask me how I know this...

Having cracked the flaring operation I moved onto advanced bending and discovered some issues with the pipe bender that I had purchased.  The tool is actually made by Eastwood (a US company) and is marketed specifically for bending brake and fuel hard lines from 3/16" to 3/8".  Actually, the three channels in the tool are actually sized for 1/4", 5/16" and 3/8" and the instructions simply state that for bending 3/16" to use the 1/4" channel.  All well and good but there is quite a difference in diameter between 3/16" and 1/4" (4.76mm vs 6.35mm) and 3/16" pipe sits very loosely within the bending channel and does not align properly with the 'stop edge' on the tool.  I ended up inserting an offcut of 2mm steel sheet between the pipe and stop edge while bending to get the pipe alignment correct in the tool.

3/16" Pipe does not sit square against "stop edge" (circled)

Using 2mm Steel spacer to correct pipe alignment in bending tool

Making a bend in a piece of pipe is as simple as inserting the pipe into the appropriate channel on the tool and supporting one end by the stop edge (with optional 2mm spacer...), aligning the zero degree marks on the stationary arm and rotating arm of the tool and then pulling the rotating arm around until the zero mark on the rotating arm aligns with the desired angle mark on the stationary arm.  Again when working with 3/16" tubing it is not possible to align the zero marks properly, and so bending to a specific angle actually requires a bit of guesswork and frequent checking with an angle finder/protractor.

Misalignment of Zero marks with rotating arm seated on 3/16" pipe 

Rotating arm pulled round to bend pipe just beyond 45-degree mark...

...however, bend is actually not quite 45-degrees

Now, this method is fine if you know where the start of any bend is on the pipe (i.e zero mark corresponds with the start of the bend).  But if you are measuring out a pipe run with multiple bends it is easier to measure the position of the bend vertices (the point where the two legs either side of the bend intersect) and then perform the bend utilising the other marks (R and L) on the tool.  And at this point, I have another issue with the Eastwood bending tool.

Clearly, at some point, the specification of the tooling has been changed, as the instructions show photos of a version of the tool with cast markings on the rotating arm and clearly identifying the marks to use for the different pipe diameters.  The version of the tool I have appears to have engraved marks and has no markings at all for the 1/4" channel (which in any case would still not be quite correct for bending 3/16" pipe anyway).  I ended up interpolating the marks for 1/4" by scoring a line extending from the 5/16" and 3/8" marks and using these as an approximation for bending the 3/16" pipe.

Eastwood instructions showing cast marks for all pipe sizes on rotating arm
(Photo courtesy of The Eastwood Company)

Extrapolated lines for 1/4" channel - unmarked notches are assumed to be the 45-degree mark (still needs some guesstimation for 3/16" pipe)

I suppose this is all a question of 'you get what you pay for" and let's face it, the Eastwood tool was a shade over £20 and a professional quality single diameter tube bender from an outfit such as Swagelok is way north of £100 which, for a single build, is just not a consideration.

So with flaring and bending techniques now sorted, it's time to make up all the necessary pipes for the Cobra.

Brake Lines - Part 2

Having come up with a suitably OTT method of fixing the brake lines.  The next stage was to plan the routing for the front brake pipes and the clutch pipe.

The brake lines will be formed from 3/16" dia pipe while the general consensus is that the clutch pipe is formed from 1/4" dia pipe.

I wanted to keep the pipe runs as neat as possible with both pipes running parallel.  I also wanted to plan out where to place my bespoke pipe clips.  There is no guidance on the fixing of brake and fuel lines within the IVA manual.  The only reference to a distance between fixings is for electrical cables/wires, which according to Clause 8 of the General Construction section of the IVA manual, "must be...secured at intervals of at least every 300mm...".  The general view amongst the kit car community is that this is applied to the fixing of brake and fuel lines as well.

Having done all that I basically followed the AK suggested routing (as have most other AK builders), although as I appear to have too much time on my hands, I modelled the pipe routing and clip positions in CAD.  One slight change I did make, however, was to adjust the suggested position of the 3-way brake union on the offside chassis rail to give a slightly longer pipe length to the connection with the offside flexible brake hose; most other builders have commented that this short length of pipe is a pain to bend given the proximity of the brake fittings to the required bend and I figured that allowing a longer length of pipe might facilitate the forming of the necessary bends.

Pipe routing - clips at less than 300mm centres and adjusted position of the 3-way union

The plan is to run the brake and clutch pipes to some bulkhead connectors which will be held in place with a bracket mounted on the top of the offside chassis rail.  The clutch pipe will also terminate with a bulkhead connector, secured by a bracket, on the nearside chassis rail, for the flexible hose to the clutch slave cylinder to be connected to.

I acquired all the necessary brake fittings from Automec.  The bulkhead fittings are M10x1.0mm fittings (HU106) with brass locknuts (LNB2) and M10 female fittings (HU2A) for the 3/16" brake pipes and 7/16"x20 fittings (HU141) and 7/16" female fittings (HU4A) for the 1/4" clutch pipe.

Bizarrely at the time I bought the fittings Automec did not supply a brass locknut for the 7/16" bulkhead fitting - they do now, part LNB4 for anyone interested.  I spent many nights on the internet trying to get hold of brass 7/16" locknuts to no avail; eventually, I tracked down some steel jam-nuts on eBay but might upgrade to the brass lock-nuts for aesthetics at some point!

Bulkhead connectors - 7/16"x20 for clutch at the top and M10x1.0mm for brakes at the bottom

The basic configuration of the proposed bracket to secure the bulkhead fittings was "borrowed" from Stuart Holden's AK build blog.  I modelled the initial bracket in Fusion 360, which has a cunning function allowing you to generate a flat pattern for a sheet metal design, which takes into account the radius of all bends etc.  I also went a bit overboard (a recurring theme) and modelled the brake fittings.  This turned out to be just as well, as I could see from the CAD model that, with my original dimensions, there would be no room to secure the three female unions on the mid-part of the bracket.  A slight adjustment to the dimensions and the problem was solved!

CAD model of brake/clutch pipe bracket

Drawing of sheet metal flat pattern

I cut out the drawing of the flat pattern and stuck it onto a piece of 2mm sheet steel.  I used an angle grinder with a cutting disk to cut the steel close to the pattern and then used a combination of bench grinder, grinding disk, belt sander and various metal files to get to the final shape.

I centre punched the location of all the holes and drilled out the 5mm dia holes for the mounting bolts and 5mm pilot holes for the fixings.  I then bent the three tabs to 90 degrees using a vice mounted metal brake (another homemade creation!).  The fixing holes were then opened up with a stepped hole drill; 10mm for the brake fixings and 11mm for the clutch fixing.

First cut-out with the angle grinder...

...following by a variety of sanding/grinding/filing implements to get to final shape

Mounting/Pilot holes drilled and fold lines scored

Ready for bending using my DIY metal brake

Tabs bent up and fixing holes drilled out to size

The finished article - looks just like the CAD model!

I treated the finished bracket to some candy red powder coat before marking up the fixing position on the chassis rail, drilling and tapping for some M5 bolts and securing in place with some stainless steel Allen-head M5x8 bolts.

Bracket after powder coating...

Mounting hole locations marked up on chassis prior to drilling and tapping

Bracket secured in place with M5x8 bolts...

...and complete with bulkhead fittings.

Now it's time to start running some brake lines!

Rear Axle Strip Down - Part 7 - A Fatal Extraction

With the rear hubs now all nice and shiny after their trip to the sandblaster, it was time to tackle one of those tasks I was not looking forward to.

When stripping down the rear hubs, the heads of the two smaller screws securing the brake backing plate to one of the hubs had sheared off.  Now it is time to attempt to remove the remaining parts of the screws which are still stuck in the hub.

Today's mission - removal of two sheared screws...

There are many suggested ways, it seems, to remove broken screws and bolts.

The most straightforward would have been to position a suitable sized nut over the top of the sheared-off screw and using a hot metal glue gun, blob some weld into the middle of the nut to join it to the screw.  Then it should just be a matter of using a spanner to undo the nut/thread combo.  My only issue with this was that the sheared-off thread is just below the surface of the hub and, while the theory is that the steel weld won't stick to the aluminium of the hub, I wasn't prepared to take that chance with my hub.

Next on the list of discarded options was the use of a suitable sized screw/stud extractor.  The theory behind these is that a pilot hole is drilled into the broken screw into which the extractor is inserted; the extractor has some reverse cut threads that bite into the metal and undo the screw.  Now I have never had much luck with using screw extractors even on screws in wood with chewed up heads.  And given that these broken screws had resisted all attempts to remove them initially before breaking, including heat, impact screwdrivers and penetrating oil, I seriously doubted that using an extractor was suddenly going to persuade these screws to give up their grip on my hub.

So the method I decided upon was to slowly try and drill out the broken screws, using drill bits of increasing size until the hole is drilled out to the diameter of the screw shank and then to retap the hole with the required thread size.

Of course, I should have known it was never going to be quite that simple.

The first problem is that actually trying to centre punch the end of a sheared-off screw is quite difficult - the broken surface was uneven which made it hard to locate the punch in the exact centre. In hindsight, I should have used a Dremel or similar to grind the end of the screw flat before using the punch...

The second problem was that smaller diameter drill bits are very short, the chuck on my drill is quite large and the offending holes are very close to the hub bearing housing; the result that I could barely get any depth to my initial pilot holes in the screws using a 2mm bit.  Worse to get any depth I had to fix the drill bit with only a very short length of the shank actually in the chuck.  This means that the drill bits are very flexible and the end is prone to wander (of course compounded by the difficulty of punching the centre of the screw in the first place).

Drilling depth restricted by the clash of the drill chuck and the hub...

The end result was that the pilot holes on both screws did not really start off on centre so by the time I started opening the holes up with 3mm and 4mm bits it was clear that the holes were going very awry.  The other issue is of course that with the hub being aluminium the drill bits found it much easier to slip off the hard steel surface of the screw and chew their way through the softer aluminium.

Opening up initial pilot holes...

By the time I got to the 5mm bit, I realised I needed a Plan B, as the result was that I was drilling out about 3/4 of the area of the screw and the rest of the hole was through the aluminium hub.

Plan B was to use a Helicoil kit (thanks to that well known on-line retailer and their next day delivery service).  Helicoil inserts are a threaded metal insert used to repair stripped threads; the stripped hole is drilled oversize and tapped for the metal insert which is then inserted into the tapped hole to reinstate the original thread.

My logic for this approach was that by drilling the hole slightly oversize for the Helicoil that this would allow me to remove all the remaining portion of the screw thread from my misaligned drilling.

Helicoil Kit - includes drill, tap, insertion tools and a selection of inserts

The hole in the hub should be an M6x1.0 thread so the first step was to drill out the hole using the supplied drill bit for the corresponding insert.

Prior to drilling - misaligned attempt to drill out screw is clearly visible!

After drilling - operation didn't quite clear out all of the remaining screw

Next step is to tap the holes for the Helicoil inserts using the tap provided for the M6 inserts.

Tapping holes for inserts.  During...

...and after

Next stage is to insert the Helicoil.  The inserts have a small tang on the bottom of them which is inserted into the slot on the appropriate sized insertion tool.  This is then used to twist the insert into the threaded hole until the insert is approximately half a turn below the surface.  Care needs to be taken to allow the insert to thread itself into the hole without applying too much downward pressure.  My first attempt unwound the bottom of the insert... Fortunately, it was not too far into the hole and I managed to extract it without too much excitement.

M6 threaded insert in place on the insertion tool

The final step is to use the punch supplied with the kit and a sharp tap with a hammer to break the tang off the bottom of the insert.  

One repaired hole!

Replacement screw fits perfectly!

In the end, it was not as traumatic a job as I was expecting it to be (although equally, it was not a simple as I would have hoped...).  Both holes are now repaired albeit both are slightly off from where they were originally.  Hopefully, the brake backing plate will still line up - if worst comes to worst I may have to slightly oversize the holes in the backing plate.

Right, time for a cup of tea to celebrate.