Getting a 1940s Moto Guzzi GTV back on the Road

[JoJo357]

That's funny Rich, i have some legitimate pictures somewhere, but these are more fuN.

*M.A.D.*

[chuckthebeatertruck]

Friday in Chicago was not warm. It was a whopping 2F when I walked to the train. I thought surely the weekend is shot for bike testing.

I was delighted to learn meteorology is not in my skill set. Saturday dawned sunny and with 42F. woo hoo!

I spent a couple hours chasing oil and fuel line fitting leaks. i wound up flashing the cones on the fuel line fittings in the solder pot to “reface” the sealing surface. This deposits a thin, sacrificial layer of soft lead. However, the left petcock taper was so worn no amount of flashing could build it back up. The taper was worn eccentric and while repairable with a few more hours work, i took the lazy approach and soldered the petcock in the open position and added an in-line petcock.

For those unfamiliar with these type of early petcock, they use a tapered cone pulled by a spring to mechanically seal. You often can lap them if they drip. But, once the taper wears eccentric, fuel escapes down the taper and there’s no seal. Fuel fitting grease can slow the leak, but i assume eliminate it.

With that done, the carb overflowed. Float is correct and “floaty,” so the seat was suspect. Lapping with 220 clover helped, but it’s time to track down a new seat or make one. I decided to just leave the petcock half cocked to more or less match the overflow.

All right, finally ready to ride!

Damn thing won’t even cough. , ,and then i notice the high tension lead is loose on the plug. Fix that and boom, the old guy lit on the second kick. Despite the imperfect carb, the bike idled well and didn’t blow smoke.

I clicked it into gear on the center stand and it had terrific clutch feel. Time to ride.

I have to admit this is the first time ever that all the bs i read about riding these bikes is 100 percent true. It was the most natural pointing bike i’ve ridden in a longtime and very light. It felt exactly like a very good prewar bike, but with suspension that works. Power was surprisingly good and torquey. 20hp, but well done. Clutch is very light and there’s zero snatch. Brakes are light, good, and surprisingly progressive. Controls are ergonomic and feel good. Bike is quiet, but the exhaust valve does squeak on the over-run under high engine braking. I’ll need to keep an eye there to see how it beds in after a tank of gas.

I did about 5 or 6 miles just puttering until the cold creeped in.

The voltage regulator crapped out and spiked the voltage enough to blow the fuse. So far, this marelli dynamo is challenging me ;-). Beyond that, it seems i just need to deal with the carb drip and off we go.

I think i’ll enjoy riding this one and am very glad i didn’t give up on finding one.

[RichO]

Excellent!

[Rubone]

Let's fix that...
38ULH reverse image.jpg

[chuckthebeatertruck]

Over the past couple of years, I have continued to enjoy my GTV putting on more than 1100 miles on various runs. Considering 55mph was a good cruising speed, that's a fair amount of saddletime.

However, not all was smooth sailing. We had three persistent problems, which are the point of this update.

Problem 1) Clutch Throw Out Bearing - this is a weak point well known for failure. I machined a new body and replaced the loose roller balls with a caged wafer bearing and hardened washers. What a huge difference!

Problem 2) Constantly running rich and inconsistent metering. The original carb was just plain worn out. Rather than sleeve, rebuild, etc -- I set it on the shelf and made up a custom ring to mount a Del Orto VHB29 as used on many 1965-1971 Guzzi models. Instantly solved all carb problems. But . . . I made a really stupid mistake in jetting which was compounded by problem 3. In sum; I meant to install a 152 jet and some how installed a 125 when I realized the 145 jet was a bit lean at the upper end. Well . . . that didn't work so well and the top end got VERY hot. Hot enough to melt the nylon in the incorrect head nuts.

Problem 3) The felt oil seals in two areas had broken up and there was RTV all over from a really bad attempt to stop a leak in a simple cover. Together, the bits of RTV and little tiny bits of felt were constantly plugging the return side of the oil system. This meant I'd have a bottom end full of oil . . .but nothing else -- which made things run sluggish and hot.

So, when I was out testing jetting . . . I wound up with a soft seizure. Bike never stopped, but it slowed way down. I parked it and towed it back to the shop. It had cooled by then and started right up. But, I knew better than to keep going.

As a result, I pulled the motor apart a couple of weeks ago. Here's what I discovered:
1) Only the top end had ever been apart. The piston was on it's first oversize the part number suggests it was installed prior to about 1960. The bottom end was all original and never split!
2) The cases were the most sludged and crap filled I've encountered in recent years. The cases soaked in solvent, spent 90 minutes in the parts washer with naptha based solvent, spent another two hours being boiled with detergent, then got washed with a pint of acetone AND a pint of toluene. That finally got the deposits and stuff out. Total was about 4 hours per case half. Vapor blasting would have been a way better choice.
3) Every single part in the bottom end was within wear limits. That was unexpected.

The bore, however, was 100% shot. It was heavily taper worn and egg shaped -- with relatively deep scoring. The piston was in remarkably good shape with only some soft seizure marks on the skirt margins. Much of this was due to Guzzi specing a brand new piston to cylinder clearance approaching .006. Add in the taper wear and the piston had almost .015 at some points! It's pretty hard to fully seize a piston with that much clearance!

Much to my amazement; only ONE part is not readily available - and it is the valve adjustment screw. No problem; I'll make new ones from 4140 and harden the tips. Pistons; however, are really weird. There are replacements but they are all low compression and odd sizes. New ones are stupidly priced.

My solution; find a sub. After measuring I realized that the GTV piston is almost identical to a Harley 74" big twin piston. I ordered up three NOS pistons in low, std and high compression. Indeed, the compression height and ring lands line up perfectly. The pin boss is a bit too narrow, but easily corrected in the mill. The pin is slightly larger than stock; but the wear on my original components mean it was actually worn TO .791 and a harley pin just about fits. Some light honing and we'll be in business. A photo showing the three pistons is embedded. I'll chose later on in the process.

I went over to my sunnen and honed the cylinder back to round and true. I wound up needing to go large enough that an .040 over shovel piston is a perfect fit.

The second reason for posting is the unexpected. I had contacted Piaggio and gotten the history of my bike. It left the factory at the end of July 1948 for a dealer in Turin (and came to me with a Turin registration). When I opened the cases, I found the builder marks. These include the date on which the cases were matched and the engine built. My cases were marked 08/07/48, which translates to July 8, 1948.

So, yesterday was the 78th birthday for this particular motor.

Fun little things.

The old guy should be back on the road with a fresh top end and cleaned out cases by end of August.

And, yes, I changed that 125 jet for a 152. Won't make that mistake twice.