LMIII top-end refresh question

[KnowFear]

I am about to dive into disassembling and inspecting the barrels and heads on my recently acquired LMIII. The odometer shows 18,896 miles, but there is certainly more since the speedo cable was broken and probably has been for some time. Maybe 25,000 miles for a conservative guess?

Both head gaskets have clearly been leaking. My plan is to disassemble the heads for inspection, and pull the cylinders to inspect bores, pistons and rings. I will replace the base and head gaskets, and valve springs.

MY QUESTION: Is there anything else that I should replace on spec, while I'm in there?

Thanks all.
Chris

 

[Morizzi]

Hi Chris,

Before I pulled it down I'd do a compression or leak down test to know what you have. I'd be prepared to get the valve guides K-lined and the valves machined to seal.

25,000 miles? I think you are being very optimistic. The odometer only goes to 99,999 so it could be once or twice around the clock. I've got a LM III that I think has been around a few times. Check the carby jets. LM III's had lean burn carbs. Many owners re-jetted them with the result of washing the bores and causing excessive wear. If your main is over 125 then take special attention. OEM was 115 from memory. I run one of my LM III's OEM and the other is 120 with a 268 atomiser instead of 115 and 265 so it is a bit richer but I do live at sea level and the plugs burn OK.

Nigasil bores need rings to suit. Make sure you get the proper ones if replacing. No good getting 850 rings for an iron liner like the LM II.

Washers and shims for the rocker gear may be worn but it is unlikely to be an issue. I've never replaced mine, just turned them around.

Whole lot of controversy about honing nigasil but I do. There should be hatching visible, if not I give them a light hone. If there is a slight recess under the wear lip I'll even give that area a light rub with some wet and dry paper by hand. Yes, I am a heretic and not going to Guzzi heaven. :lol:

Ring gap minimum is 0.4 0 - 0.45mm from memory. The damn things will run with a gap of 4mm or more so don't get too stressed. If gap is well under 1mm I'd have no hesitation in throwing them back in.

If you find rubber bits in the oil feed galleries then it may be the internal oil feed hose that runs externally to the heads from the middle of the V. If in doubt replace it. You don't want that gallery to be blocked.

Replace the O rings around the studs and the gaskets of course. Don't forget the big O ring under the top stud cover. The small hardened washer is often missing under that top stud nut too. You may want to get new ones or grind down some regular hardened ones to fit down the access hole. A 10mm allen key adapter to a torque wrench is useful too when torquing the heads. They can't be too wide or they won't fit down the hole.

That's all I can think off off the cuff. Good luck with it.

Cheers

Rod

 

[KnowFear]

Hi Rod,

Thanks for the detailed reply. The engine is on the bench, so I'm out of luck for a warmed-up leak down. I didn't think about it before I tore the bike apart. Is it worthwhile to do a cold one?

I'm pretty sure the bike hasn't gone around the odometer yet. It has suffered from bad storage and just sitting around, but it just doesn't look like a high-mileage machine given the wear. It is very original, but not sure about the paint. Also, it's clear that the engine and tranny had never been separated until I did it.

Chris

 

[Morizzi]

Hi Chris,

If you can do a cold leak down it may be handy but don't go to too much trouble. There are no valve stem seals, only guides. Pretty hard to tell if they need K lining but not impossible. I use kerosene to see if the valves are seating and the guides are sealing. Some people use oil but I find Kerosene faster and it cleans as it seeps through. Fill up the void, position the head and wait to see how long it takes for the Kerosene to seep through. If in doubt get a good shop to K-line the guides and machine the valves so you don't need to lap them. Well worth the expense and safer as grinding paste can get into lots of things.

Have a look at your clutch plate thickness and the hub splines. MK III's came with the shallow square teeth on the hub. Latter models came with the deep V teeth that were more resistant to wear. They will tell you how much the bike has done. Plates new are 8.0mm and should be replaced at 7.5mm from memory. I'm too lazy to look it up, that's your job! :lol: If new plates and hub are needed go for the deep V. If not then I use a brush to coat the hub teeth with a fine layer of moly fortified grease. That will help prolong them as does a higher idle speed, balanced carbs and not holding the clutch lever in for too long at stops. Yes I know you are'nt supposed to use grease in a clutch system but as I've told you I'm a heretic and not going to Guzzi Heaven.

If the motor hasn't been turned over for a long time then pour some engine oil down the spark plug hole and so the rings get lubricated. Allow it to sit for a fair while just in case they have become stuck to the bore before rotating the crank.

The big end nuts are expensive so leave them alone if you can. They should be replaced every time. The barrel can be slipped down over the rings by hand. If you have a ring compressor that comes apart that will do the job but I do it by hand. The trick is to have the barrel perfectly in line with the rings. Ease the first one in by hand. I use the flat side of a screwdriver and make sure I don't mark anything to push the ring in gently as I apply even gentle downward pressure to the barrel. I'm sure someone will gasp and terrify you with tales of horror using a metal tool like that. Do I need to remind you about the heretic thing? If you can find a softer tool stiff enough then feel free. B)

I use 515 or 518 gasket goo by Loctite on the gaskets. Its the red jelly looking stuff. Other makes have similar product. Use what you are happy with but I don't use anything with metallic compounds in it. Just my preference due to possible electrolysis between differing metals.

Cheers

Rod

 

[Chris R]

The big end nuts are expensive so leave them alone if you can. They should be replaced every time.

Wot Morizzi said but the nuts IMO don't need to be replaced - they are basically under compression and never fail but the bolts should be replaced if touched and they are expensive! Indeed they are more expensive than the super duper bolts used on Carillos.

I view valves as basically scheduled maintenance items and replace them out of hand - at a minimum the exhaust valves.

The tensioner is best replaced with the agostini/valtek aftermarket one.

If you are going to replace the valve springs then the ones from the old fiat 1600/1800 twin cam should fit (they definitely fit the round head and are slightly stiffer). They are very good quality and were (at least until recently) cheap as chips.

I would also check the valve lifters - they have a tendency to pit IME.

I would not use any goo on the head gasket - just check flatness and torque them up correctly using moly and oil on the threads. Goo on the base gasket. I use the permatex spray on red gunk as it is easy to use, never dries and you can reposition the gasket if you need to but anything will do.

Ta,

Chris R

 

[KnowFear]

Top-end stripping update -- initial observations:

1. guides slightly ovalized
2. zero clearance on one exhaust valve (valve bottom was mousey brown, compared to the other one which was black)
3. outer valve springs all measured 52.5mm free length (in spec as per factory manual)
4. inner valve springs all measured 44mm free length (manual specifies 45mm and indicates that they should be replaced if shorter)

I've sent the heads to a local retired aircraft mechanic who does expert head work. He does a lot of BMW airheads, so I expect he'll know what needs doing. I'm inclined to replace guides and all valves.

QUESTION is this: do I really need to replace the inner valve springs?

 

[john zibell]

Top-end stripping update -- initial observations:

1. guides slightly ovalized
2. zero clearance on one exhaust valve (valve bottom was mousey brown, compared to the other one which was black)
3. outer valve springs all measured 52.5mm free length (in spec as per factory manual)
4. inner valve springs all measured 44mm free length (manual specifies 45mm and indicates that they should be replaced if shorter)

I've sent the heads to a local retired aircraft mechanic who does expert head work. He does a lot of BMW airheads, so I expect he'll know what needs doing. I'm inclined to replace guides and all valves.

QUESTION is this: do I really need to replace the inner valve springs?

I'd replace both springs (inner and outer). If one is under spec, the other will be in a short time. Also using a K line is more durable and cheaper than replacing guides. If your guy doesn't install K-lines, take it to someone who does.

 

[KnowFear]

I'm thinking of using Kibblewhite guides and valves. Apparently their nickel-bronze guides are very slippery (according to the aircraft head guy) and are very durable.

I've asked around regarding K-liners and nobody seems to know what I'm talking about!

 

[contractor20]

http://klineind.com/Valve-Guide-Liner-R-System.html

 

[Penis Rotor]

The big advantage of K-lines is that they will retain a bit more oil so wear is slower but most importantly when installed with the disruptor and reamed back to size the bore remains concentric to the seat so ess material needs to be removed in the re-seating process prolonging the service life of the seats.

Bashing guides in and out also risks damaging the heads so if you can avoid it? so much the better.

Pete

 

[rolf j]

You get a fantastic head start on your engine job with all the good advice from people on this forum! I may chip in a couple minor comments, but all that matters has already been said above.

K-lines surely seem to work well and they cost pittens compared to a full guide job...and definately I would be concerned when someone was going to bash my guides in&out of the heads as Pete Roper mentions! Purists believe there is an issue of reduced head-dump capacity with K-lines, but I wouldn't worry on a street machine when many racers seem to be happy with the K-lines.

Regarding valve cutting, there are experts and there are "experts", I've tried both extremes and it makes a difference! You find those who cut the seats&valves as if they worked on a lawnmover, and I've also had one in my engine. Try to ask how many angels he uses or whether he recommends radius cutting. If he can't answer straight, answers "one" or doesn't know what you are talking about, find someone else. The horsepower and everything else that goes with it like fule efficiency etc., is produced in the top end and according to ol'school of hotrodding the valve job is more important than many other issues up there.

There are more than one opinion about the need and usefulness of honing/sanding nicasil cylinders. I never bother to touch them as you can even find the original hone marks in an old engine! What more useful are you going to do by repeating this now, when virtually all the bedding-in seem to take place at the rings only? I would have changed the rings and all set to go!

rolf j

 

[KnowFear]

Rolf - thanks for your input. For some reason I forgot to check the ring gaps after tear-down. I finally checked the mid-bore ring gaps today:

compression ring gap, both = .55mm (factory manual spec .30 to .45mm)
middle ring gap, both = .60mm (manual says .30 to .45mm)
oil scraper ring gap, left = .75mm, right = .85mm (manual says .25 to .50mm)

MORE QUESTIONS !!!

1. I'm going to order new rings, but I'm not sure what to ask for. The pistons and barrels are marked "A". Is that all I need to specify?
2. Out of curiosity, how badly worn are these rings?
3. On both compression rings, I am unable to feel or see a chamfered edge (is there supposed to be one?)

Thanks!

 

[KnowFear]

Goo on the base gasket. I use the permatex spray on red gunk as it is easy to use, never dries and you can reposition the gasket if you need to but anything will do.

Ta,

Chris R

I was on a roll tonight, and I forgot to put anything on the base gaskets. Arrgh. Is that going to be a problem?

 

[john zibell]

KnowFear,

The factory didn't put any sealant on the base gasket. You should be OK. I wouldn't tear it back down and have to replace both the base and head gaskets at this time. It is easy enough to do later if a problem arises. Although a little sealant is good insurance on the base, it isn't absolutely necessary.

 

[Bretino]

The earlier Lemans models have rubber o-rings that fit down on the cylinder studs topside of the cylinder - you will want to pick out the old ones and replace them if you have these on the LM3. Order them in advance b/c it will hold you up when you go to reassemble. (I am not sure if they are on your model.)
Years ago shortly after I got it my 850Lemans developed a hissing cylinder (right side) and finally lost compression - when I tore it down the cylinder bore was corroded on the outer side as if water or moisture had seeped down thru the spark plug hole or head gasket and pooled and eroded the metal. That led to a complete top-end rebuild with forged pistions and upgrade to 998cc - that required fly-boring the cases.
You shouldn't have much trouble with this work - it is all fairly straightforward.

(Okay I think this thread is old now...just noticed the original post date..!)?

 

[Bretino]

compression ring gap, both = .55mm (factory manual spec .30 to .45mm)
middle ring gap, both = .60mm (manual says .30 to .45mm)
oil scraper ring gap, left = .75mm, right = .85mm (manual says .25 to .50mm)

Hi again - well you must also measure the piston ring lands - that is the up and down play of the rings in the piston grooves - because the piston ring grooves may also be worn beyond spec. You don't want to install new rings in pistons that have worn ring grooves. I have seen this happen - especially on high(er) mileage engines. Alas! Sometimes that "re-fresh" turns into a "re-build" - hopefully not in your case.

Cheers!

 

[Larry H]

Hi!

I know this thread is a wee bit old but I use it anyway as my bike is old and my questions are about piston rings.

My bike is a LM1 which I am slowly (unfortunately) renovating. Today I removed the piston rings and checked the end gap in the bores (cast iron with next to no wear, no noticeable step in the bore surface where the piston stroke ends, only a colour difference).

Both 1st compression rings are within spec at 0.35 and 0.40 mm (spec 0.30-0.45mm).
Both 2nd compression rings are outside spec at 0.55 and 0.60 mm (spec 0.30-0.45mm).
Both oil scraper rings are outside spec at 0.65 mm (spec 0.25-0.40mm).
Is it a common occurrence that the different rings wear so differently? Anyway, I will buy new rings and install.

The other question is about the possibility of a spring behind the oil scraper ring. Currently there is no spring but for some reason I kept the old rings from last time I replaced them (a long time ago) and together with that old oil scraper ring there a spring. I do not remember where that spring comes from but checking the spare parts manual and work shop manual there is no mention of a spring.
So should a spring be fitted or not?

Next I will remove the valves and check the guides etc. I have checked the valves for leakage and both exhaust valves leak so at minimum I will have to grind them.

Cheers,
Larry

 

[scottmastrocinque]

Is it a common occurrence that the different rings wear so differently?

It is not unusual. They are constructed differently and of differing metallurgy and they exert different forces on the cylinder wall in different ways.

The other question is about the possibility of a spring behind the oil scraper ring.

I can tell you that some oil rings utilize a spring expander to apply additional radial pressure to the piston ring.

However I am uncertain on your application.

Are you using OEM parts (if they are even available for a bike this old)?

V700Steve or one of the other guys who work on really old stuff might know the answer to this. Unfortunately John Zibell is on vacation and he would know for sure.

 

[V700Steve]

The expanding spring you talk of comes with the ring set, it is not a separate item. Something to think of when choosing ring sets.
On the valve sealing issue. I clean valve on wire wheel to clean off deposits, same with seats. Then I inspect & lap valves & seats to see if they need a trim or if they now seal. I would also check guides for play.

 

[Larry H]

Thanks guys.
The rings I checked the gaps on yesterday were fitted to the pistons many years ago and I believe they are original spare parts as I still have a the Ricambi originali cartons with the Moto Guzzi spare parts number on them. Inside these cartons I found the rings that were the old ones at that time (typical me). But in in the cartons I also found the expanding springs which were not fitted and I do not know now if they should have been fitted or not. Hope this is not too confusing.
I will order new ring sets, it will be interesting to see if expanding springs are included or not.

Steve, I will take your advice re the valve/seats.