V7 tune up – 23 Apr 2015.

It has been clear to me that the V7 “loop” hasn’t been running properly. When started, the right hand cylinder would warm up well before the left. It wasn’t running on one cylinder but the one on the right was clearly doing the majority of the work. The carbs were also not synchronised and when the throttle was closed with the engine off you could hear click click as the two slides came to rest. I have already changed the plug caps as one gave me a shock and noticed the distributor cap was cracked.

Valve clearances.

These have to be done with the engine cold and I mean left-overnight-cold. The workshop manual and owners handbook for the V7 give valve clearances as 0.1mm inlet and 0.2mm exhaust. The Chiltons manual I’ve got says 0.15 and 0.25mm but it seems that these are for the 850 models. So after checking on This old Tractor I went with the factory settings. They were way out on the left cylinder but closer on the right. I shan’t go into exactly how to check the clearances as it’s much the same as when I did it on the S3 here.

Cylinder compression test.

As I’ve got a compression tester I thought I might as well use it! It’s a cheap one I bought many years ago when I was into classic cars. It takes both hands to hold it against the spark plug hole while the Mrs holds the throttle wide open and pushes the starter. I got a reading of 132psi on the left and 140psi on the right. These are close enough to each other to be acceptable and are high enough. Both figures are reached in 4 revs.

Apparently you can work out roughly what the reading should be in psi from the engines’ compression ratio. As the V7 compression ratio is 1:9 then the reading should be 9 x 14.7, which is the atmospheric pressure at sea level, plus an amount for an increase caused by the heat generated by the compression process. That comes out at 132 plus a bit. Pretty good then I reckon.

The HT circuit.

I started by removing the contact breaker points but found that they looked almost new. So, they went back in and the new ones have been saved. Points gap is 0.42 to 0.48mm. I set them at 0.45 then turned the engine so the other cam opened the points and found the gap was too small. Readjusting them got the gap in the specified range for both cylinders.

I replaced the rotor arm and distributor cap with new, made up new plug leads and refitted my new plug caps. I started the bike and it ran better already.

Ignition timing.

I made a start by removing the three screws that hold on the generator belt cover. I had expected to see a pulley with 4 timing marks as described in my various books. However I do remember seeing something about some V7s only having 2 marks which is what I initially appeared to have. Turning the engine to TDC on the LH (No 2) cylinder didn’t bring any marks in line with the arrow on the crankcase. The pulley had been fitted “one bolt out” so was 120° off. I removed the pulley which is in 2 parts with shims in the middle to tension the belt. When I looked at the back half of the pulley there were 4 marks but they don’t look right and only 2 appear to be original.

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The left hand pair are deeper and it’s possible to see where they were punched into the rim. The right hand pair seem to have been cut with a file. Given that the marks (if there are four) should be TDC, 10° BTDC, 20° BTDC and 38° BTDC they would be spaced differently to how they are. I made the marks more visible with a permanent marker pen. They look more like 0, 10, 30, and 40° BTDC.

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The rear half of the pulley was then test fitted to see where it lined up at TDC on the LH cylinder.

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So that’s right now. I refitted the drive belt and the pulley halves with the shims.

Now, when I dismantled the pulley there were the 5 shims between the 2 halves as expected but also a washer on each bolt hole acting like a 6th shim. I replaced the 5 shims without the extra washers. I turned the engine as I tightened everything up as I was worried about trapping the belt in some way. I then checked the belt tension using a spring balance. Correct belt tension should allow 10mm of deflection with a 10Kg pull. You don’t want it too tight or the generator bearings will suffer. If you need to tighten the belt you move a shim from between the halves to outside. I thought mine was fine but we’ll be back to this soon!.

I could now proceed ignoring my concerns (right or wrong) about the pulley markings as I was going to statically time the engine. The other 2 would be for dynamic timing with a strobe light. Static timing is to the second mark from the left as you look at them, ie 10° BTDC on the left cylinder. If I’ve got this wrong please someone, let me know!

I removed the spark plugs and turned the engine to get to this setting then loosened the clamp holding the distributor. I mounted a test bulb between the contact on the outside of the distributor and earth and switched the ignition on. I needed to turn the distributor a very small amount to get it set correctly so that, as the engine is turned (clockwise looking at the pulley) with the 26mm crankshaft nut, the light comes on just as the markings line up.

Air cleaner and intake boot.

Before tackling the carburetors I decided to clean the air filter. To do this the filter box had to come out and I then found just how badly damaged the boot connecting the filter box to the carbs was.

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It was totally split underneath where I couldn’t see with the filter mounted. The filter itself was beyond cleaning as the “flock” surface had worn off. Replacements were ordered from Gutsibits in time for the order to be sent out to arrive the next morning.

Refitting the rubber boot and filter gave me an hour or so of entertainment. I’m used to fitting the boot to the V7Sport’s carbs so I had an idea of how to do that. You remove the right hand carb inlet stub using a “hook wrench”. Next grease inside the rubber boot at both carb connections and fit the loose RH stub. Then fit to the LH one that’s still mounted. Finally bend the boot so that you can screw the RH stub back on to the carb.

I then found that I couldn’t get the filter box containing my new filter back on without removing the battery first. Several attempts were made to refit the filter box so that the rubber intake boot fitted over all of the lip on the box and its lower part went inside the “well” in the filter box lid. I had to grease both parts to do it and found it helps to swear as you try and manipulate it with sore fingers. I did have to remember that I live next to a primary school and the workshop doors were open.

Finally a seal was achieved and the battery could go back in.

Carb synchronisation.

In the past I have sync-ed Guzzi carbs by setting each cylinder to fire so many times before stalling, setting idle mixture by ear and then shoving my fingers up the intakes and making cable adjustments by feeling for the slides to move together. This time I decided to take a more scientific approach and used a pair of vacuum gauges. The V7 didn’t originally have vacuum take off points but at some time the intake manifolds have been drilled to provide some.

I haven’t got any photos of me setting up the carbs as I couldn’t do the 2 things at once. I basically followed the instructions given here on This Old Tractor even though that suggests gauges are useless and only carb sticks will do. Surprisingly, I found that the gauge needles didn’t bounce all over the place but were pretty steady and it was easy to get the 2 sides to match.

After the adjustments I found that the throttle stop screws were 10mm out on the left and 11mm out on the right. The idle mixture screws were proud of the carb bodies by about 1mm on the left and about 0.5mm on the right.

The bike now starts easily when warm and idles properly. I let everything cool overnight then tested cold starting using the “choke” lever. The bike fires easily.

I took the bike for a test run of about 50 miles and it performed beautifully. It pulls well, “doesn’t run out of puff” like it did and even the gear changes feel better! What I did notice was the occasional squeal from the generator belt. I think I’ll have to add the washers I left out before. I suspect the belt fitted isn’t the correct one and I should replace it.

Sorry this has been such a wordy post lacking in photos. I promise I’ll try better next time.

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