Head gasket replacement

Lyndoneil

Lyndoneil

Full member
Location
Towcester uk
Hi guys
Slightly hesitant to ask, as I could get trolled, but here goes.
What's the considered opinion, about using a thin smear of wellseal on either surfaces when fitting a new cylinder head gasket to a Laverda .
To do or not to do?
The bike in question is a 500, has blown the head gasket, oily mess!
Am going to remove the head to check that it is not warped.
 
A thin bead of Loctite 510 is fine. Check both head and barrel surfaces for warping, head gasket failures are pretty rare, usually something wrong if they blow.

piet
 
Depends on the type of Head Gasket and surfaces you are working with; for instance:
1/ Hi-Quality Specialty head gasket like a James or a Solid Copper; use nothing - Ensure mating surfaces are True and Clean
2/ Composite and thin Steal Shim Head gaskets I generally paint both sides of the gasket with Hi-Temp Aluminum Paint.
3/ Ultimate is to use a thin copper gasket with and Dike ring machined into the top of the Cylinder bore. (Dike Ring is not the term but I'm close)
 
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Apart from once when I used a car formulated product, many years ago, I mount them dry.

From reading around, it would seem that 500 head gaskets are pretty prone to blowing.

Paul
 
Paul Marx said:
Apart from once when I used a car formulated product, many years ago, I mount them dry.

From reading around, it would seem that 500 head gaskets are pretty prone to blowing.

Paul
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The gaskets are fool-proof Paul, it's the heads that are the culprits. Most have a big valley at the front, between the chambers. Also causes the exhaust cams to bind.

piet
 
Hard to tell if you have a warped Cly-Head; Could be as simple as a hole in the Manifold tube, Leaky Carb Gasket, or Crank Shaft Seal where when you torque to specs from a blown engine and you end up with blown head gasket upon rebuild - Know your friendly machinist to ensure the Cylinder Head to Engine Block mate perfectly with no Warps.

By then I would do a complete Valve job with new valves, guides and springs and do a little Hi-Perf Porting and over sized light weight Valves, seat angles, play with Carb Jets and Exhaust Pipes - Nothing like a 1970 8000rpm Breganzie Twin. She's by no means the fastest but a hound you can not escape. ;o)

Basically, if you Blow a Head Gasket the Valve Seats will NOT escape undamaged and you got Warped Cylinder head ;o(

Perhaps the Engine has NOT been fired up for 20 years the head Gasket simply ROTTED away with all the other Composite and Rubber Gaskets when the engine heated up - Count your blessings you got a simple total engine tare down an replace all seals - GOOD LUCK !

PS: The valve seats should NOT be any more then .016" to .018" on the intake and more then .020" to .022" on the exhaust after machining. Considering you chose over sized light Valves to repair the seat damage with a little chamber to bowl porting - Preferable with new guides and springs - BaSIC hOT rODDING and Engine repair ;o)
 
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The top of the engine had not long been rebuilt, maybe 200 miles running comparatively poorly. Mostly due to the pickup wires being totally corroded and having had the wrong mixture screws in wont have helped
I'm hoping the oil was only blowing out only, as there was no smoke from the exhausts, I haven't retouqued the heads, worrying enough just touqueing to spec as everything on these look so fragile.
I need to remove the cylinder head anyway to make sure the valves and pistons have clearance, as it has S1 cams and hi comp pistons, plus l want to check and remeasure all the cam clearences. So I might as well ensure the barrels/cylinder heads are true just for peace of mind.
I guess I could do stuff to the head, but really, I'm more concerned with getting it running right and oil tight.
The new ignition after fitting improved the running immensely, although still not perfect, but didn't have the opportunity to sort out the last 10% of running issues, as the right side of the bike became smothered in oil after 11 miles, so I just cleaned off the mess and parked it up in the workshop corner last May, to sort out during our winter.
I guess I was a bit pissed off with it at that point.
 
sfcpiet said:
The gaskets are fool-proof Paul, it's the heads that are the culprits. Most have a big valley at the front, between the chambers. Also causes the exhaust cams to bind.

piet
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Piet, I'm sorry but on the 500s the gaskets are not fool proof. Ask Robin Webster, Dave Fitz, Austen Kears or me. We have ALL had failures (okay during racing) where it was the gasket that was at fault.

The problem is that on some gaskets, the cylinder head bolt holes cut into the flame ring, making it weak - even gaskets provided by Slaters.

The solution is to make sure the gasket you are using has full width copper flame rings all round, or (as Fitz and I have done) use solid copper gaskets. I've attached a photo of a new gasket from Slaters, showing how the bolt hole impinges on the flame ring. The second photo shows what happens.
 

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the same applies to triples, I had a lump of gasket hit me in the right leg at high speed and very high load, two people and camping gear, and I was going up hill on a French motorway, when pretty much full throttle was needed to maintain 100MPH, and she blew, oil everywhere and a two pot motor. Happenned on the hottest day on record and the Sunday of the ascension weekend, possibly the busiest day of the year traffic wise, recovery took a very long time, no water after the first 30 mins, very unpleasant. The biggest mistake I made that day was not riding the bike off the motorway, because when I eventually got recovered it was by a very small Fiat van, and we unloaded the bike as far as possible, and that included Andrea as well, I then followed the van to a small petrol station where there were comfort facilities and awaited a proper truck to take us to Calais

I had drawn, programmed and made, solid copper gasket's well known to a lot on here, I have sold a lot, and on my own engines, after a very intesive week of develeopment, removing and stripping the motor four times, I have never had a failure, plus on several that I know about, and at one time worked on, plus odd people who come up to me on occasions and say "hi, I have got one of your gaskets fitted" Cutting the flame ring to gain clearance for the four O rings is MADNESS, (better off with no O rings and the old style gasket) that is why I did it, and I still use them, its worse on a 1200 as there is no upstanding liner spigot which engages on the recess in the head as on 1000's, but both gaskets are identical 1000 and 1200, I also machine the top if the block flat so as the gasket face and liner are the same plane (not easy on a 1000, but still doable for a skilled machinist) not 20 thou lower as factory spec in order to achieve a small amount of "backing" effect retaining the gasket, they (moto Laverda) must have known all along that this is a week spot, this changes the compression ratio a tad and in some cases valve to piston clearance (never heard of a clash yet) and has the effect of making the timing chain look a little worn, it could be compensated for by making an aluminium base gasket 20 thou thicker, but never had to, so didn't bother, I don't care about any of that, my gaskets stay in place.

CLEM
 
From my experience, if liner/barrel geometry is correct, the composite gaskets with the slight cut-out in the flame ring work perfectly well, in twins and triples. This has been discussed to death...

There are lots of poorly- and/or incorrectly-made gaskets on the market, many barrels and heads in desolate condition are in use and asked to perform flawlessly. Often, a combination of both cause constant frustration. I seriously doubt that stock flat-topped 500 pistons alone would have caused the gasket to blow in that manner.

Clem, the design of the head/barrel joint is not a weak spot, it works fine as long all is as intended. It is just that these bikes were not built to last 40 years and more... Massimo wanted to sell us a new bike every 4-5 years, same as every other manufacturer. A simple metallurgic process of alloy shrinkage leaves the liner proud after countless heat cycles, leaving the flame ring to do all the work. Lots of old Honda and Kawasaki air-cooled fours show exactly the same symptoms.

A recess of 20 thou equals 0.5mm, no head gasket in the world will bridge such a gap reliably. The liner recess should be 0.2mm MAX.!! 0.10-0.15mm is better. Used with a suitable gasket, this is quite OK for road or track use. I've built several track-only motors that have run for many years without a single head gasket-related issue. Flush barrel/liner fitment calls for a dead-flat gasket, but in no way will a slightly proud liner allow a head gasket to seal properly.

piet
 
This all sounds like an avoid a Laverda 500 at all costs conversation to me. You would probably be better off with a Honda CB350K. I always fancied an Alpino but it doesn't seem like they are worth the bother ;)
 
While they do command a little more mechanical sympathy than a CB350, they're not much different to the bigger twins and triples in regard to repair and maintenance.

Wifey claims her 500 has been more reliable than all the jap bikes that she had before. 50000km certainly take their toll, but the bike has been brilliant over the last 30 years.

piet
 
pf1 said:
This all sounds like an avoid a Laverda 500 at all costs conversation to me. You would probably be better off with a Honda CB350K. I always fancied an Alpino but it doesn't seem like they are worth the bother ;)
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Just wait until the cam starts wandering around in the CB 350 head.
Paul
 
The 500 actually hasn't required much, worst would be a sprag clutch bearing that gave up on our honeymoon trip in '98. Fixed en route at Willis' place. A broken clutch cable and seized shocks come to mind a few years later. The shocks were NOS Konis, fitted about a month before leaving for a vacation in Italy. A friendly italian moped/scooter shop operator kindly let me use his workshop, the guys had never seen a shock absorber being opened and overhauled.

Apart from that, just the usual consumables and perished rubber bits.

piet
 
Did better than Chris P, someone noticed the top eye on both of his shocks were almost cracked through just at the top of The Alpine Way the things you notice on the side of a mountain road. Luckily we were a couple of hundred ks round trip from Icon World Headcourts in Albury so Brett went and bought a set of replacements.
 
Vince said:
Did better than Chris P, someone noticed the top eye on both of his Chinese shocks were almost cracked through just at the top of The Alpine Way the things you notice on the side of a mountain road. Luckily we were a couple of hundred ks round trip from Icon World Headcourts in Albury so Brett went and bought a set of replacements.
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Fixed....
 
Yer, I wasn't sure on that point. It had me perplexed that Chris would do that, all his bikes are usually in absolutely top condition for purpose. Maybe Leno the previous owner did it before Chris acquired it from Leno's widow. Death-defying failure that's for bloody sure. That was day 2 or 3 so that bike had done some serious punting at speed on some typically rough alpine roads before it was noticed He was again so lucky.
 
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