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Moto Guzzi engine build

by

Niall McLoughlin

With winter now firmly upon us, it's the time to do the all-important modifications/updates ready for testing/validation, fine tuning and use in the coming spring and summer.

I'll start off by saying that this is the first engine rebuild/strip down I've done – and I've learnt a lot along the way.

After a tip-off from Mike Meakin, I acquired a 1991 Moto Guzzi 750T engine in the spring of this year from just south of Surrey area. I originally planned on fitting this to my new build. However, in September managed to get my grubby little mitts on a complete 1994 Nevada with only 10k on the clock and an MOT for a price I couldn't refuse – thus two Guzzis for two Pembletons!

Engine before strip
complete bike

This meant that I could do an engine swap on my current SWB Pembleton first, and learn all about it, ready for when I start the new build. I have decided to rebuild the older engine, and install this into the current Pembleton, then put the later engine with less miles and less wear in the new build with very little mechanical work, just a check over and a visual tart up.

I bought the older engine from a Guzzi club member who clearly knew a thing or two about these bikes! He had just rebuilt a bike for his wife (possibly a Jackal) and I counted two other complete Guzzis in his workshop and countless "bits". He was breaking his old 750T as the final drive had seized. The bike had about 45k miles on it and I managed to get pretty much everything I needed apart the carbs. He recommended stripping down and checking the big end and main shells and changing all gaskets and seals. He also warned of the exhaust valves prone to burning out, so recommended to re-grind these and leave the valve clearances a little loose and just put up with the tappety tap (factory settings are 0.2mm exhaust and 0.15mm Inlet).

With the engine sat around all summer and the weather getting poorer towards the end of October I decided it was time to open her up and see what's what. Fortunately the seller gave me a disc with technical drawings, workshop manual and exploded engine diagrams with comprehensive parts list.

As this is the first engine I've pulled apart, everything I removed was labelled and all the nuts&bolts were put in marked storage tubs to ease the rebuild.

The strip down was very straightforward and most parts came free after a good soak in WD40, some whispered cursing and gentle persuading!

cut down drill bit in hole
screw in
rotor popped off

Once you have the front plastic alternator cover removed and the stator is off the rotor, you need to undo the bolt from the crank end. Once it's off you then need to insert about 60mm of 5mm bar or cut down Allen key into the end, then wind the bolt back in. The rotor is held on a taper, so as you wind the bolt in, it works like a screw jack, and the rotor will pop off. I'd suggest doing this bit with the engine lay flat on its back as it'll pop off at a fair old rate. I cut down a long 5mm drill bit that had blunted and used that and it worked fine. (This is the only part that had me scratching my head – it really is all very simple stuff if you're methodical about it)

slotted cap-head

Some of the socket cap-heads rounded and required a slot cutting in them to enable the use of a big screwdriver.

The order of disassembly that I did was as follows:

  1. Empty all oil and leave to drain overnight! Or you'll get oil everywhere – trust me
  2. Rocker covers
  3. Front plastic cover
  4. Alternator, ignition and chain cover (MAKE A NOTE/MARK THE ORIENTATION)
  5. Valve rockers and push rods (make sure at TDC first)
  6. Heads (you can just about get a deep socket on the inner bolts with a gentle tap)
  7. Timing chain and oil pump (BE CAREFUL NOT TO LOSE THE KEY, ITS TINY!)
  8. Oil filter and sump (I had to drill one of the bolts out here as it was stead fast)
  9. Split the block – one of the nuts had seized here so I had to cut and split it. The 10mm socket nuts are tight!
  10. Once the crankcase is split, keep an eye on the spacers/shims at the back of the crankshaft!
  11. Remove the big end bolts and remove the crank, leaving the pistons in the cylinders
  12. Inspect the main shells and the big end shells for wear
  13. Carefully pull out the timing cam (lock pin/bolt on top – more details on this later). You will get some resistance from the vacuum, but it just pulls out.
  14. Inspect for wear and remove the cam followers, label them as you go. The cam is hardened so once it's worn it needs replacing!
  15. Remove the barrels and pistons together.
  16. I removed the pistons carefully and inspected the barrels and rings. All excellent condition bar a little carbon deposit, which came off after soaking in Coca-Cola for 48hrs or so with a soft scouring pad.
worn shells

Everything in my engine was exceedingly good, with the only visible wear on the big end shells and main crank shells, which will be replaced.

At this stage it's pretty much entirely apart, so go through and remove the gaskets and any seals, the gauze filter in the sump and any other fittings. I left the valves in at this point as I didn't have a valve spring compressor at the time and it makes little difference to blasters if you're planning on removing and grinding them in later.

bare parts for vapour blasting

I sent images off to three or four firms in the end, including those who specialise in classic motorbike restorations. The quotes back varied massively, however the cheapest quote came from Boris Blasting in Wellingborough. He didn't have a website, but was very friendly and the more I researched, the more excellent reviews I found. I turned up to some obscure small but busy industrial estate and found his unit in the back corner. He seemed to really know his stuff and I can't recommend him enough! The castings returned as per below and were turned around in one week for under a £100

Castings back from blasters

After rinsing and drying all the components at least twice thoroughly to remove all the blasting residues etc. All the new parts arrived that I sourced them from various places. The biggest spend by far was with Stein-Dinse in Germany. On the whole they were cheaper than Gutsi-Bits, they had all the parts in stock and I found it easier to search by part number on their site.

New parts as follows-

new bits

Now that it's all back from the blasters it's time to re-finish. I masked as required then VHT black paint on the barrels and heads, rubbed back the edges of the fins and VHT lacquer on everything.

The paint I had recommended curing for 40mins at 160C. With the wife visiting a friend one weekend I had the house (and the cooker) to myself. If she ever found out I even considered this I think my head would be separated from my shoulders and on a spike for the birds! However, although a very mild smell was left in the oven afterwards (soon masked by baking some garlic bread) she was none the wiser, the perfect crime! (Unless she reads this! The Editor)

VHT paint baking in the oven
Painted engine parts before assembly
Polished rocker cover

I removed the and reground the valves. Then put all back together in the same order it was removed with new oil filter, spark plugs, gaskets, seals, big end shells, main crankshaft shells and all stainless fixings!! To prevent galvanic corrosion/seizing, the fixings have a very light smear of aluminium anti seize grease on them. When re-assembling I fell foul of a few things that I should've noticed sooner. I'll list them below to help prevent others doing the same:

Cam fixing bolt

When re-installing the timing cam, there is a hole in one of the bushes at the end at the rearward most part. This MUST be facing vertically upwards (shown by B below), as there is a pin (A) that engages in it to hold it in place from above / external.

TDC position

When doing the valve clearances and ignition, the crank does two revolutions for every one revolution of the timing cam. The easiest way to determine TDC is with the timing chest cover off. This is when the two markers on the cam and the crank are vertically closest together for the right cylinder, and when they're furthest apart for the left cylinder (looking at the engine from the front)

The front plastic cover had pretty heavy scoring on it. I know that aluminium covers can now be sourced for around £90, but for the moment I rubbed down the one I had and gave it a spray in metallic aluminium paint and lacquer. Personally I quite like the way it looks.

finished engine 1
finished engine 1
finished engine 1

This particular engine came with a Saprisa ignition system mounted on the front of the timing cam underneath the alternator cover. I'll try and get this working first as the previous owner said he had no trouble with it at all. Next step is to get it in the car and plumb it in! For the sake of expedience, I plan to fit the carbs from the bike to this engine with a pressure regulator and facet pump, then get brand new carbs for the next build.

I won't bore you all with the next steps as this is already well documented (and I haven't done it yet), however, I felt there was a bit of a void on here for the engine side of things. There is a video on youtube of the strip down.

At the time of submitting, the engine has not been fired up or tested – I will report back for the next ePAG with an update as to how it goes!

A copy of the Moto Guzzi Workshop manual for the small block engines as well as manuals for Dellorto carburettors are available in the technical pages section - the Editor

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