M20B28 build in full

Due to the car being off the road because of the broken wish bone we decided it would be a good idea to tackle the engine rebuild. This was more planned for next winter but never mind!

The current engine had 111k on it, and with the zone chip started running really well so we were not expecting any major issues. Part of the rebuild will involve dropping an M52B28 crank shaft and M20B20 conrods into the block. This will make it a square engine with an increase in capacity to 2.8ltrs. Further the head will recieve a new set of performance valve springs and a dbilas 282°/272° camshaft. All gaskets and seals are also being replaced.

Update 1/1/2009 – I’ve been asked a few times what shells we used. They are standard M20 shells (also standard size as the crank was not reground). The piston rings also standard M20.

Head off!


Inspection of the head reveals its in prett y good condition!

Nice tip for getting the bolt out the end of the cam shaft. Put the old timing belt around it, then loop the open end of the belt round the work mate. This locks it in place and allows the easy removal of he botl!

Rocker number out, shaft on its way out

Camshaft and everything else removed from head minus the valves

First valve out, could take any more out as the valve spring clamp we bought was not big enough, needs to go back for the more expensive one!

Rather than buying a new valve spring compressor we decided to make an extension for the curent one. 

After lathing the tube to the correct size with a suitable amount taken out the inside to fit over the clamp it needed holes in the side so that you can still remove the collets after compressing the springs:

The completed adapter attached:

And now in use on the head to remove the valves. Looking at this it would seem that it would have been possible to use it without the extension but it would seems to be easier this way up!

The intake valves and valve seats look great, but the exhaust seats and valves need re-grinding. They are just starting to pit. All in all everything seems to be in very good condition.

All the valves, springs and collets arranged in order waiting to be cleaned up.

 The head could do with a dip, it seems to be nice and straight but I think I’ll find a machine shop to double check everything for me!

The head is off to the local machine shop for crack testing, we’ll know if everything is good on Tuesday. If it is then it’ll get a bit of clean up.

Clean valves! This took a lot of time! The exhaust vales were cakes. Used a technique from Jason (GreatOldOne) placed the valve in drill and used increasingly finer sand paper to take the layers off and then some metal polish to finish it. The intake valves just need a run over with 1200 grit & some degreaser, then metal polish.

This was a 4 hour process with two people and two drills so about 8 work hours to clean them up! Some of them still have a bit of carbon build up but its very small and they still need to be run throug the ultrasonic cleaner and degreaser!

The tops of the valves where cleaned like the bottom half, the centres took a bit more work with sand paper and the edge of a knif blade. The only area left alone was valve seating area, that will be ground in when the head comes back from the machine shop.

Rest of the engine is out of the Sportster, looking a bit empty now.

Engine and gearbox out!

The clutch coming off

Sump off!

6 pistons removed from the block and numbered. They need a good clean and the conrods swapping for the 130mm M20B20 ones. I’m going to check the M52B28 conrods and the M50B25 ones I’ve got knocking about as well see if there’s anything more suitable.

Bores in the block look great!

Flywheel off, had to lock the crankshaft in place with a metal bar between piston 3 and 4 then the bolts came out really easy!

Crank bolt came out really easy – surprisingly!

M52B28 crank shaft sitting in the M20 block – this end will need some kind of spacer for the oil seal.

Crank sits in the block like it was meant to be there – only other thing that need to be tested is the M20B20 130mm conrod with the M20B25 pistons in place to check clearances.

One more picture for good measure!

One question, how the h*** to do you the cam belt pulley off the crank? It seems to be wedge solid. The cam chain pulley came right off the M52 crank so I assume its the same with the M20 except I’ve got 20 years of gunk keeping it on!

Puller-me-jig in place. The metal plate is bolted to the bit that needs to come off. In the middle a long bolt (out of an M52 block!) and a nut. Theory is you do up the bolt in the middle and it pops off.

The metal is already bent from the first time it wont done up (it moved about 1/2 mm)

Carefully the middle bolt was done up until it started pulling off.

and here it is finally!

There were tiny amount of rust underneath which is what was causing it to stick.

Needs a good clean out and polish before test fitting on the M52 crank.

M20B25 piston fitted with M20B20 conrod and M52B28 crank! Moves well.

Piston / conrod / crank combo at top dead centre – looks good 🙂

Crank spacer taking shape on the lathe

One step left is to machine down the spacer to the correct size – about 18mm

Spacer machine down to size, about 17.90mm with in 0.1mm of the original.

Cam belt pulley test fit, this a very tight fit so it will need the “the tool” to get it back off again.

As the M52 crank nose it a bit longer than the M20 the washer in the front doesn’t sit flush.

Washer in the lathe, need to take about 1.25mm off giving 0.1mm space between it and the crank nose.

Finished off and the edge smoothed off

Test fit of all parts on the M52 crank.

Comparison: M52B28 crank and the front and M20B25 at the back

Cleaned up all the pistons today, but manage to snap one of the piston rings in the proces – doh!

Andy, the chap who came up with the conversion severl years ago has recommended I use the standard head gasket with this conversion!

One more discovery after examining the head, its not quite straight – its warped ever so slightly towards the front where the thermostat sits. Check with a steel ruler, but to be 100% sure I used the lathe bed which confirmed it. Off to the machine shop with the head next week then!

Silver is so last month, so blue it is this time!

We used red hamerite on the exhaust plugs and those didn’t discolour until we welded something on it – so it seams heat resistance enough!

The hammered blue looks great out in the light.

Oil pump disassembled and cleaned. It all looks fine nothing really worn so no need to replace it.

The parts slot right into place, covered in assembly oil. This stuff is thicker than normal oil and kinda sticks to everything. Should help keep everything lubricated on the fist run.

The filter element has a few hardended clumps inside it but nothing major!

Got the head back from the machine shop on Friday, they took 4 thou off to remove the warp: 

Starting a bit of valve lapping

2 down only 10 to go!

All the valves boxed up and ordered

Throttle body attaches here, its been ground a bit larger – more pictres to follow on that at some point

Valve springs – the larger one has shrunk 2mm over the inside ones and new springs.

All valve lapped in – a simple short sentance that will take you hours and hours, especially if you have pits on the valves like we did!

A nice mat grey colour is what your after!

The valves all have a nice mat dull finish on them as well.

Valve stem oil seals going on – a size 11 socket bit proves to be exactly the right size to push these in place.

One at a time the new schik valve springs go in, putting the colletes back on proved to be a very fiddly proceedure!

All springs now in place!

All cleaned up – the head needed a “4 thou” skim to take the warp out of it.

Camshaft inserted

New oil seal and o-ring for camshaft

Rocker shafts and rockers on their way back into the head – the head needs to be propped up so there is room for the valves to open as the last rocker needs the camshaft rotated to slide in. Also make sure the rocker shafts are at the right angle before rotating the camshaft otherwise its not easy to move the into the correct place.

Both rocker shafts in and the clips that hold the rockers in place. The spray bar as also been mounted.

A closer view of the assembled head

Everything now in place on the head, it just needs the rocker cover put in place to shield the inside from dust.

New parts! Conrod bolts, main bearing shells, big end shells, water pump, cam belt and piston rings.

2.8 crank installed in the block with new bearings, bolts are torqued up.

Crank spacer in place

Many hours later all the pistons are installed with new bearings, all moving parts have been given a coat of assembly grease – this is more sticky than normal oil so it should stay put until the normal enigne oil is circulated round the engine before first start.

Front cover plate in place with new oil seals installed.

Oil seal around the crank spacer.

Water pump installed along with the gear for the oil pump.

Bottom view of engine with all parts installed. New conrod bolts have been torque, then turned to the approated settings!

Blue sump! Just resting on the engine for photos.

Its not quite this bright in real life, the flash has given it a much strong blue colour!

Final clean up and degrease of the head.

Mmm shiny! Also double check that the cam pulley is turned to the timing mark on the head.

Belt tensioner now also installed

Head gasket placed on the block.

Head placed on block ready for the head bolts to go in.

Bolts placed, these were all tighten up as per the Bentley manual and in the correct order. Its a 3 step process.

Everything bolted up, the rear oil seal needs to go and the sump bolted on.

Final thing was to install the cam belt – turned the engine over severa times and it all sounds good. No interference between valves and pistons from the sounds of it!

Rear cover plated attached to block, sump bolted on and the flywheel on read to be bolted. The bolts need to be tightend up in a specific order and covered in loctite.

Clutch back on the fly wheel

Gear box slotted on “like a glove” [ace ventura]

After a lot of jiggling the engine is back in mated with the drive shaft and on all 4 mounts.

Just needs all the ancillaries bolted back on

Nice blue block, shame it has to be covered by the intake manifold!

On the road again:

Sorry you’ll need Flash installed to view this video!

March 2008 back on the road again!

March 2008

March 2008

March 2008

March 2008

March 2008

March 2008

March 2008

March 2008

March 2008

Social profiles