Engine stripdown and crankshaft modification

Engine stripdown and crankshaft modification

So, here’s a little job I wasn’t really expecting to be doing. As I mentioned in an update to my engine trial fitting post, I had made a bit of a rookie mistake in understanding the different crankshaft noses found in Rover V8s, and the long nose of my 4.6 just wasn’t going to work with my stock GT V8 front-end configuration, so some drastic action was needed. The 4.0 and 4.6 engines used in the P38 Range Rover (of which my 4.6 is one) had a longer 90mm crank nose to drive the oil pump, as compared to the 70mm nose of earlier variants. It also has a longer woodruff key than the earliest engines for the same reason, but that is not an issue in itself (these differences are quite well-covered in the book How to Power Tune Rover V8 Engines for Road & Track, as I discovered later!). Here’s what mine looked like (also note the very suspect looking woodruff key):

The problem for the MGB V8 conversion is quite well illustrated by the picture below of my mocked up front end. The back of the original GT V8/P6 crank pulley, when slid as far onto the crank nose as possible for the pulley bolt to tighten against the front, only just reaches the timing cover, and it’s clear to me now that getting a good oil seal would be next to impossible. I’ve also bolted the timing pointer in place here to demonstrate how far adrift it is from the timing marks on the pulley!

There was quite a bit of head scratching at this point. Given the overall popularity of MGB V8 conversions, there must be a good sized subset of those projects that have used a 4.6 engine, and a good subset again that have at least tried to use a factory GT V8 front end setup, so I was a bit surprised to find almost nothing written about this issue on the web. Apart from a couple of old questions on forums with vague answers about shortening the crank nose as a solution, I really couldn’t turn up anything useful, so I decided to throw caution to the wind, whip the crankshaft out, and then have 2cm chopped off the end of it! It will either be a glorious success and work perfectly, or I will have wrecked my engine. Either way, the next person who goes searching for help on this issue will have a bit more to work with.

So here I am, stripping down the engine. I would have been doing some of this anyway – I have some newly rebuilt heads to fit, and I had just about come around to the idea of fitting a warmer camshaft, so I satisfied myself that dismantling the bottom end was not too much of an additional chore. The previous owner had done some refurbishment work fairly recently in the engine’s lifetime (new bearings etc.), but the service parts are fairly cheap to renew again, plus I’m really enjoying the learning experience, and kind of like the idea of building the engine back up to a completely known state later on.

I enjoyed myself so much in fact that I failed to take a lot of photos, so this section will be brief. Rocker covers off, and then the rocker shafts themselves were removed. The former owner had rebuilt the rockers on new shafts and they still looked perfect to me, so I kept them intact and will probably just put the complete assemblies straight back on later.

I used the trick of storing the pushrods in numbered holes in cardboard to maintain their positions, but as I’m going to be using a new camshaft and tappets in the reassembly I’m not sure how vital this is(?) – better safe than sorry.

The pistons and old heads had what looked to be fairly heavy carbon deposits to me, but I’m nothing like expert enough to know if this is a ‘reasonable’ condition for an engine with supposedly around 2000 miles since a rebuild. The pistons are the originals and it’s possible that the previous owner did not clean them up too much during the refurbishment, so it’s hard to know the true state of things here. I’m glad that none of them exhibit the ‘steam cleaned’ look which I believe is a telltale sign of a potential cracked block, so hopefully that is not something I will need to worry about. The cylinder bores are in good shape without any worrying marks or damage, and I measured them all to be within original tolerances, so at this point I’m only planning to clean and refit the original pistons with new standard rings during reassembly.

Eventually I was down to the completely bare block, so it was a perfect time to give it a really thorough degrease and clean to get it looking more presentable. In this state you really get a feel for how lightweight this aluminium block is – it’s so much easier to move around the workshop without all the heavy metal bits attached to it!

Stripdown complete, the crankshaft was straight off to the machine shop for its nose job. I went to a local engine specialist that I’ve used before, and they did a fine job removing the extra 20mm – they also drilled and tapped the pulley bolt hole a bit deeper for me, to ensure the bolt would still screw in to its full depth. Some might consider this an extreme course of action I guess, but faced with the multitude of issues that extra 20mm was causing (pulley to ARB fouling, poor oil seal, water pump/alternator pulley misalignment, timing pointer position) I think this is a pretty neat solution, and since this crankshaft is not going to be driving an oil pump again I will not lose too much sleep over it.

The dodgy looking woodruff key noted earlier actually broke in two whilst it was at the shop, and when I prised what was left out later on it definitely had a very homemade look to it (bottom of picture above). I replaced it with a genuine Land Rover part for the princely sum of £11.

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