New to forum, and to Moto Guzzi—1975 850T refresh

[Sculpt-dude]

Hello. New here, and starting a 1975 850T project. I am very experienced with 1970s BMWs, but this is my first Moto Guzzi. I have always wanted one. This one has been sitting a long time, so I will be going through it fairly thoroughly. But, it’s mileage is pretty low (not sure if the odometer is working, but it’s only 11,000 on it, and it’s not 111,000).

But, out of the gate, my question is about the chromed cylinders. There is some flaking, and I’m wondering how serious this looks.

There was a considerable concentration of flakes in the rocker arms. Is that a common collection point? Are there other spots like that? I assume I should certainly pull the con rods and check the crank there. Do I have to tear down the whole thing?

Obviously, I will be replacing the cylinders.

Thanks for taking a look, and I look forward to being a part of this forum.

 

[john zibell]

Just so happens my first Guzzi was an 850T and even the same color. I purchased it new in 1975. Just to be on the safe side I would recommend investing in 850 Gilardoni cylinders and pistons. Just because of age the chrome bores will be suspect. As to what you are finding at the rocker, that is a different story. When Guzzi makes the rocker the end hole for the oil passage is plugged with soft material. They don't clean out the threaded hole for the retaining bolt and that bolt will chew into the plug giving you the debris you find there. The fix is is to run a tap through the hole then blow out the passages. The T also has a poor shift return spring that will fail. Have it replaced with the updated spring. Also note that the rear brake shoes are much too grabby and it will often lock putting the bike sideways. Bending a curve in the brake rod diminishes that locking tendency.

 

[Sculpt-dude]

Just so happens my first Guzzi was an 850T and even the same color. I purchased it new in 1975. Just to be on the safe side I would recommend investing in 850 Gilardoni cylinders and pistons. Just because of age the chrome bores will be suspect. As to what you are finding at the rocker, that is a different story. When Guzzi makes the rocker the end hole for the oil passage is plugged with soft material. They don't clean out the threaded hole for the retaining bolt and that bolt will chew into the plug giving you the debris you find there. The fix is is to run a tap through the hole then blow out the passages. The T also has a poor shift return spring that will fail. Have it replaced with the updated spring. Also note that the rear brake shoes are much too grabby and it will often lock putting the bike sideways. Bending a curve in the brake rod diminishes that locking tendency.

Thank you John, very good to start getting the fine details of Guzzi engines.

One more thing I noticed was wear on the valve stems. Not major, I think. However, I know that BMW designs their valve keepers to allow the valve to spin, and even the wear pattern out. Am I seeing typical wear for a Guzzi? Or are these valves stuck?

 

[john zibell]

Stuck valve implies it doesn't go up and down. Can't answer that question without seeing the head and valves. As to seeing a "line" across the end of the stem it isn't uncommon.

 

[Amboman]

I would recommend a complete engine strip and rebuild. Why? Because chrome flakes have likely made their way through the oil pump and have possibly embedded in the main bearings. Also, there's likely a deposit of sludge in the sludge trap inside of the crankshaft rod journal. If enough sludge collects, it can block the oil holes to the rod bearings.

Hopefully chrome flakes haven't been grinding away at the crank and oil pump. Early 850-Ts didn't have an oil filter - only a fine mesh strainer. Yours may have though - if it does, then in addition to the 14 socket head cap screws around the perimeter of the engine sump, you'll also have 4 on the bottom surface. Two at the front and two at the rear, could be either hex head or socket head.

You'll also want to replace the timing chain tensioner with one that actually does the job.

 

[Sculpt-dude]

Well, thanks, Ambo. I do have an oil filter, but I don't imagine that changes the equation all that much as to needing to tear it down. Or does it? (Being irrationally hopeful.)

Well, I wanted a winter project...

 

[V700Steve]

When you drop the pan, look for metal. When you pull off filter cut it open and look for metal bits.

 

[Amboman]

Even with a filter, the sludge trap can collect enough to warrant cleaning out.

 

[john zibell]

Even with a filter, the sludge trap can collect enough to warrant cleaning out.

Be sure to order a new plug when you do this. The existing one may become distorted. Also stake the new plug when you install it.

 

[Sculpt-dude]

The pan had only fine slime/sludge—no discernible metal bits one could feel.

I cut open the filter and washed the paper in mineral spirits. This is all that came out. About 1/4 of that came up on a magnet. There is nothing obviously “metallic” about the remaining grit. If I didn’t know anything about the engine it came from, I would call it “dirt.” But maybe that’s what the chrome debris looks like?

 

[Godfrey]

You can pull a rod bearing cap without tearing down the engine. Pull one and look at the bearing. If there's no scoring, IMO just go forward: put a new filter in and fresh oil, refresh the top end (Gilardoni cylinders and pistons are an excellent idea), and run it with some Castrol GTX 10w40 for 500 miles, then drain and refill with fresh oil again.

Your engine sounds like it has very low mileage ... under 50K miles and there's generally not enough time for substantial sludge to build up in the crankshaft to the point that it warrants the total engine strip down needed.

I miss my Sportified 850T. Racer is a good substitute, but that specific bike was so sweet...

 

[Sculpt-dude]

I checked my odometer today, and it works, so I’ve only got 11,000 miles. I like the sound of that diagnostic—if the chrome isn’t evident in the rod bearings, it’s probably not lurking anywhere else. On the other hand, if it’s embeded in the crank bearings...

I haven’t yet researched how much is involved in pulling the crank.

Still, I haven’t yet seen anything in there that looks like chrome particles.

Thanks all for the feedback.

 

[Godfrey]

To pull the crank out and check the main bearings, or clean the sludge trap, takes removing the engine and transmission from the frame, removing the transmission, removing the clutch and flywheel, the distributor, the oil pump dismantling the timing chest, unbolting the rear main bearing, then removing it and lifting the crank out. In other words, it's both "dismantle the entire bike, and then dismantle the entire engine".

I doubt very much that it needs anything like that with mileage that low. The damage to the cylinder plating has to do with a very long period of sitting and not being run. So cleaning up the heads and replacing the cylinders and pistons will set it right.

 

[Amboman]

This was the sludge deposit removed from a 7k miles engine:

Your engine, your choice...

 

[Sculpt-dude]

Another little discovery. Pretty deep gouges in the flywheel. Interferes quite a bit with the clutch plates. How would this happen? And is it common? I will de-burr these, of course.

 

[john zibell]

I've seen grooves worn into the sides of the flywheel teeth but not across the top. Looks like the intermediate plate may have spun. I recommend replacing the intermediate plate.

 

[V700Steve]

Pretty odd for a bike w/11K mi on it. I would think it could be a rivet came out of the friction plates somewhere and got stuck. I would continue using the flywheel but not the plates or center w/o careful inspection.
The riveted clutch friction plates has plagued Guzzi and continues to do so. An 08 Norge has had 3 sets, last one is aftermarket and works great. All changed under warranty.

 

[Sculpt-dude]

Yeah, some aspects of this bike look like 11K, and some others make me wonder as well.

The friction plates look fine. A little under 7.5mm, so I will replace them. The springs are below spec as well. The pressure plates and intermediate plate all look fine. No evidence of any incident, and they are flat as can be, but also not brand new. They show normal wear.

So, presumably something broke loose in there and made things bind, skew, spin, whatever. They replaced the parts...but they didn't de-burr the damaged splines?!? I mean, that inner pressure plate didn't want to come out past those burrs.

 

[john zibell]

Yeah, some aspects of this bike look like 11K, and some others make me wonder as well.

The friction plates look fine. A little under 7.5mm, so I will replace them. The springs are below spec as well. The pressure plates and intermediate plate all look fine. No evidence of any incident, and they are flat as can be, but also not brand new. They show normal wear.

So, presumably something broke loose in there and made things bind, skew, spin, whatever. They replaced the parts...but they didn't de-burr the damaged splines?!? I mean, that inner pressure plate didn't want to come out past those burrs.

You do want to update the clutch plates and the clutch hub (4mm teeth) that attaches to the input shaft of the gearbox. The 850 T has the old style 2mm teeth that will give you problems at about 40K miles. Just do it now instead of later.