2.1 MV Rebuild DG case!!!

[123-jn]

I now have a set of DJ pistons so have a difficult choice to make. The MV pistons are 93.980 and the DJ's 93.991, Both sets appear to be in good condition although one of the DJ's has some blemishes on the side of the combustion chamber that need smoothing. I think something got in there and melted!! Anyway you can't tell now I've smoothed it off. So what do I build? An MV or a DJ. The DJ would give more power but could not be blown in the future, The MV would give less power but could be lightly turbo'd in future? I reckon I'll build a DJ for now. I still need to clearance the DG case for the crank if anyone has any tips please let me know as it looks quite complicated to hold everything in the right position so I can see where contact is possible. Has anyone done this MOD?

[123-jn]

A few more pictures here, They show my nice new nuts on a rocker shaft (2.50) from ebay for 10 which was far better than £3.00 odd each!!! They are M10x1 half nuts with a 15mm hex. Then some pics of me tapping the oil gallery for the front sender after removing the core plug (early cases don't have this one so I had to make one!!) The bore of the gallery was 14mm so I was able to tap it with M16x1.5 enabling me to use a sump plug adaptor tapped for m10x1. The last pics are of a set of DJ pistons I got from Ebay. They are shown next to a set of MV pistons for comparison. They are not in quite as goood condition as the MV's but I reckon they are ok. One of them has a slight ding on the top edge which CJH spotted, again it is only slight and I reckon it will be ok any one who knows better please let me know!! There are also some pics of the heads after rebuilding with some liquid metal in the pits in the surfaces which just needs a light final sanding now.

http://s1275.photobucket.com/user/123-j ... %20pistons" onclick="window.open(this.href);return false;

[123-jn]

ok so some pics of a piston with a slight ding in it so who has any opinions as to whether this is a problem?


http://s1275.photobucket.com/user/123-j ... %20pistons" onclick="window.open(this.href);return false;

[CJH]

Well I certainly don't have enough experience to know if that ding is worth worrying about, but it's difficult to see the extent of the damage from those photos. Do you have a photo of the edge? I would have thought that provided it's only on the top edge and the damage doesn't extend as far as the first piston ring, then you should be ok.

[123-jn]

It affects only the top 2mm down the side and as you can see is only slight, I'm not sure how I could measure it? Probably with a dial gauge. I would guess it was dropped or knocked on something. The only worry I have really is whether the stress in the metal will make it prone to cracking. I think I will take it with me to the machine shop with the barrels and get their opinion when they hone the barrels for me. Thanks for your thoughts, I appreciate any advice i can get.

[123-jn]

Hi, Hope you all had a great christmas. I've got some more pics of that dinged piston and some shots of the case where it appears some clearancing is required. It appears that relying on Go-westys little bit about cases is no right for british models . Using the standard rods I reckon I've got 2mm to take off the walls where I have marked the case on the pictures. At it's thinnest part the case is about 4.6 mm thick at the bottom of my markings . How would anyone manually do this case adjustment? With a burr and some files? The bit that go westy said would hit where the head studs are does not seem to be an issue. I was wondering if a slight tapering of the side of the rod where the bolts go through would be allowed , as long as they all weigh the same afterwards.

Any Experienced engine builders out there?

http://s1275.photobucket.com/user/123-j ... a.jpg.html" onclick="window.open(this.href);return false;

There are a few shots of my dinged piston which I also need an expert opinion on and lastly a nice stainless/alloy silencer off a kawasaki which may end up on the van.

[itchyfeet]

large dremel?
http://forum.club8090.co.uk/viewtopic.p ... 0#p8089768" onclick="window.open(this.href);return false;

[123-jn]

I have a small dremel, I will have to try the little burrs in that!!! Thanks for the idea I'll see how it goes!!

[itchyfeet]

how about this and a power drill, I think a standard dremmel won't be up to it.
http://www.ebay.co.uk/itm/36-Flexi-Dril ... xycmBS7Ll4" onclick="window.open(this.href);return false;

[123-jn]

I have one of those that I used for drilling out exhaust studs in situ!! Didn't even think of using that. Great Idea. Thanks.

[itchyfeet]

you're welcome but not really my idea...

I am amazed at the Oettinger approach to crankcase clearancing, it seems that they went for the "carve plenty out" & "just grind that off" approach by the time they got to my engine (#53)
On this and subsequent 2.5 builds I have elected to go for the more detailed "remove enough, but no more" method.


I have also done a little de-flashing inside and some detail work to remove sharp edges that could all adversely affect windage and oil drain-down. It only takes minutes but its worth it, especially if it prevents a stray bit of casting flash becoming detached...

[123-jn]

I have started to gently attack my case with the diamond burr mounted in a 6mm drill flexi extension. This is going to be a slightly longer more delicate job. It is difficult to get an angle on the head stud bosses to take material off there. Perhaps the dremel with a grinding disc may be better. I have recieved a set of standard bearings with the 1 piece thrust arrangement. The journals all measure up to spec but the bearings feel a little loose but I suppose when the case is tightened down they get 'constricted to their correct size. I notice that the old split bearings on journal 2 are heavy steel backed bearings whereas the new ones are a much lighter aluminium backed type. I hope this doesn't make any difference? They are Mahle bearings. I can't make up my mind whether to order single or double thrust cam bearings. The case looks like it will accept double thrust although I may have to make a slot for the second 'tang', or take the tang off. I need to test fit the big ends and measure the side play and oil clearance. Again the journals appear round and in spec so I have a set of standard rod bearings.

Lastly, How do I measure backlash on the cam gear and drive gear? I really haven't a clue , and how important is it that it is correct. I have a new gear on my new cam but it is not marked with a + or - . I also have the old gear marked -1 and one off a 1.9 DG marked 0 to chose from. I guess the one from the old cam should be the matching one but they were running in a different case?

[123-jn]

Well here are some pics including my cut outs for clearancing the case. I just need to put the crank back in with the pistons and rods to see if it all misses now ? Apparently you need at least 1mm clearance all round.

http://s1275.photobucket.com/user/123-j ... %20exhaust" onclick="window.open(this.href);return false;

[itchyfeet]

Bentley says backlash should be hardly noticeable 0.0 to 0.05mm
turn crank backwards and cam must not lift out of bearings or its too big (interference fit)

[123-jn]

Thanks Itchyfeet, So as long as the cam doesn't lift if I turn the crank and there is almost no play between the teeth its OK. Thanks