Engine Overhaul - replacement crank case

1st October 2008.

After reeling from my engine case problems which occured when I was overhauling the original engine crankcase. I soon realised that there really was no way that the existing case could have been bored out to 94mm to accept the new barrels and pistons I had purchased. The main reason for this was that the 1300 box used adapters to hold the 8mm heads into the crankcase These adapters are know as case savers and where fitted to the later engines. These would have not allowed the cylinders to be bored out without cutting into these threads. This would therefore have not worked. Fortunately my original case had developed problems when I taped the oil gantries out to take the brass plugs. One of the 1/8NPT plugs under the fly wheel had split the case rendering it unusable. I am presuming that there was a fracture in the case prior to me cutting the thread that had spit when I used the extracter to remove the brass plug.

I managed to find a replacement crankcase on VZi from a gentleman in the other side of Brighton. Luckily the new crank case had been bored out to 94mm already and was already machined for full flow oil. The full flow oil process requires that the outlet of the oil pump be threaded and a plug screwed in and the main oil return be taped with a 3/8NPT tap. Generally speaking the new case was in good condition and had never been line bored as it was 64mm on the main bearings.

I decided that as i did not know the condition of the oil gantries that i would have to tap them. I started by removing the pressure valves. These are located on the bottom of the case at the front and back of the engine. The pressure valves and springs are covered by a screw in plug that has a large screw driver slot in its top. The easiest way to get these undone is to tap the right side of the slot with a screw driver and hammer , so using them as a punch to knock the cap undone. With the caps removed the springs can be removed giving access to the pistons. These are usually pressed tight up into the engine. I use a piece of cane that I cut down to gain the correct width to just fit into the piston. Once you have the right diameter you can knock this into the piston so that you can twist the piston out and ease the cane and piston out.

The gantry caps could then be removed from the case. I used a 1/8 drill to drill the centre of the caps and a wood screw turned into the cap until it was firm enough to allow a claw hammer to pull the screw and the cap out together. The exposed gantries could then be drilled and taped with their respective threads 1/8NPT, 1/4NPT and 3/8NPT. There are four 1/8NPT holes that need to be drilled out to 11/32". The two 1/4NPT threads can be taped straight into the gantry as the hole is already the correct size. The two 38NPT threads require the gantry hole to be drilled out to 9/16" before they can be taped. Generally speaking you need to drill the hole a bot longer than the length of your plug. I found that when taping the threads it was better to start the thread with a taper tap. I cut down a second taper tap to make a plug that was the same length of the screw plug that I was using. With the used together I was able to get the plugs to seat below the level of the casing.

Once I had taped and cleaned out the gantries I decided I would like to get the case media blasted to bring back its surface to look like new.

I also found out via a friend that as I was building a large engine I would probably be best to locate a new balanced forged crankshaft although I hadnt figured this into my budget I new that if my existing crank failed it would damage all the other components around it and so was really not worth the risk.

Engine Overhaul - The break down

25th July 2008
Readers of this blog are aware that I had a catastrophe that was caused by a small piece of bakerlite that sat under the fuel pump. Whilst servicing a crack in this item I managed to shear of the Bakelite and drop a small piece of it into the crankcase. This was disastrous as my engine had done less than 250 miles since its last rebuild and there was no way of retrieving it other than dismantling the engine. Firstly I must say a thanks to the informed members of VZI who stated not only where the parts would end up but where they would get mashed and what they would destroy if left in situe. To be quite frank they stated the exact position. The yellow arrow points to where the bits ended up. This is just under the timing gear on the camshaft. The green arrow shows the oil feed to the crankshaft. The red arrow shows the lower pump ring that the Bakelite pump bush fits into.

To be honest I am glad VZI exists. First drain the engine oil.

I stripped the engine down in a day removing the cylinder heads by removing the rocker covers , then the rocker shafts and then the eight nuts that hold each of the heads in place. With the heads removed the barrels could be removed taking special care to get them out so far that the gudgeon pins could be removed and the pistons removed still attached to the barrels. This is a little tricky but with a pair of long nose pliers to remove the circlips the pistons can be removed by sliding out the gudgeon pins. These can sometimes be a little stiff and a warm air blower like a paint stripper is enough to gently warm the piston to make the pin slide out again. With the pistons and barrels removed the main pulley can be undone at the front of the engine. If this is tight then the flywheel will need to be locked in position. Personally I tried to use a bar between two bolts and still resorted to buying the correct tool from eBay. This fits into the top engine bolt and securely holds the flywheel so that the front pulley and then flywheel nut can be undone. The short block is then able to be split. I removed the cylinder studs and the oil pump and the oil strainer first to allow better access to the case. There are eight large 17mm bolts and a large number of 13mm bolts around the case that all need to be undone. Make sure that you have got to all the 13mm bolts as there are some that are hidden tight against the back of the fly wheel and also in other hard to get to areas. With all the engine nuts undone . The case will still be stuck together. You will need a rubber mallet or a piece of wood and a hammer to carefully knock the case apart generally speaking its easier to lay the engine on a block of wood on its left hand side so the eight large studs are facing you. There are several good places around the case that you can hit , which will break the case seal. Once you have the case halves separated you can draw the top half on the engine case of the bottom. This will expose all of the internal workings of the engine so make sure you have a large quantity of rags or cloths that you can mop up the oil slick that comes out. Before going further you need to retrieve the cam followers that have fallen into the bottom case. You also need to check that you have two dots on the crankshaft camshaft timing gear and one on the camshaft gear. these are vital to lining up the engine timing, when the hole engine is put back together. Once this has been determined remove the camshaft and cam bearings and place them in a box. Carefully lift out the crankshaft with the con rods and put this in another box with some rags to soak up the oil. You need to ensure that you have all of the bearing halves out of the engine.

With the cases bare you can start to mop out the engine oil. It is generally better to get your case professionally cleaned if you can locate someone who will do it for you.

I have purchased a new Bugpac camshaft and a barrel and piston Marle forged set-up that will bring the engine CC to 1914cc when they are fitted. I will need to acquire a new set of heads before I can have the case altered to fit them. These are very expensive and I will have to work out which ones re the best to use for their respective cost.

Next I will remove the oil plugs and re-thread them to allow for any eventuality that the engine needs in the future. I ordered the brass screw caps 3 x 3/8 NPT , 2 x 1/4NPT , 5 x 1/8th online from http://www.airlink-compressors.co.uk/Fittings/plugs.htm, unfortunatly thier website ordering was down and I had to telephone the order through. In the mean time I had to find a 9/16 drill bit and a 1/32 or American R size drill. I choose the 11/32 as I already had one. The next challange was to locate the taps. My tap set came with a 1/8NPT trap but finding a 1/4NPT or never mind a 3/8" NPT tap was going to be a challange. I posted a wanted advert on VZI to see if anyone had any.

I started cutting the threads for the 1/8NPT this seemed fairly straight forward. I had to shorten the tap I was using to allow me to get the thread further into the crank case. I fitted the brass plugs into the threads as I went. I then retrurned to them to remove them finding one had stuck tight. Foolishly I tried to remove the plug after the allen key slot rounded in the plug. I used a screw puller and to my horror cracked the crankcase around the gantry
Was this the end for the crankcase would I need to buy a new engine?