Head Gasket Leak Near Left Exh

batrider said:

I bought mine new. The dealer was supposed to do it at the first service at 500 miles. Then it started leaking after getting some miles (5000) on it and it was time to replace the head gasket.

Last time, I retorqued mine at 5, 50, 100, 250, 500, 1000 and 2000 miles. A little nutty maybe. Should be stone cold and one by one loosen it before retorquing. Adjust valve clearance afterwards. On a 750 with roadster tank you can do it without removing the tank so it's no big deal. Don't know how the 850 is.

I don't have the thread inserts so always did it to spec. Especially the 5/16 nuts in the front. If you add 5 ft-lbs to everything it will be larger percent increase for these two. I don't like that idea at all but I'm a nobody.


Russ

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Well I guess I'm nutty too. That is pretty much how I do mine. I always figure you can't re-torque them too many times. I have been known to pull out the toolkit and check them in front of the motel when I was not sure they had settled in yet.

It seems to work. The only time I have ever had a head gasket failure was when the studs near the exhaust port pulled the threads. Even then it was not a major failure, just a small oil leak and an increase in blowby from the breather. Jim

MS850 said:

Well I spoke too soon, rode to work today and found a oil leak coming nuts #9 and 10.
SOB, :evil:

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It drips when parked, why, there is no oil pressure.

MS850 said:

It drips when parked, why, there is no oil pressure.

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Pushrod tunnels aren't under pressure. Only crankcase fluctuations. How's your breather check valve/reed valve?

Nater_Potater said:

MS850 said:

It drips when parked, why, there is no oil pressure.

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Pushrod tunnels aren't under pressure. Only crankcase fluctuations. How's your breather check valve/reed valve?

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I give up where does the crankcase breather chack valve live. on the timing cover?

The breather hose from timing cover goes to the top of the oil tank, near cap, and the other vent hose on top of the oil tank towards the front vents to the atmosphere.

MS850 said:

The breather hose from timing cover goes to the top of the oil tank, near cap, and the other vent hose on top of the oil tank towards the front vents to the atmosphere.

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Air blows freely from vent hose through the oil tank, through the engine and out the rocker cover(cover loosened).

MS850 said:

I give up where does the crankcase breather chack valve live. on the timing cover?

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Unless you or a PO fitted one, then it won't have a breather check valve.

L.A.B. said:

MS850 said:

I give up where does the crankcase breather chack valve live. on the timing cover?

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Unless you or a PO fitted one, then it won't have a breather check valve.

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thanks LAB, yes it has no check valve.
It acts like excessive crank case pressure, like rings aren't seated.

MS850 said:

L.A.B. said:

MS850 said:

I give up where does the crankcase breather chack valve live. on the timing cover?

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Unless you or a PO fitted one, then it won't have a breather check valve.

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thanks LAB, yes it has no check valve.
It acts like excessive crank case pressure, like rings aren't seated.

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That is why most people install crankcase breather check valves.

PS, get a little spray foot powder and spray it around under the banjo bolts. Oil that shows up around the front two bolts often ends up being from a small and invisible leak from the oil line banjo fittings. A little foot powder will make the invisible leak visible. Jim

That is why most people install crankcase breather check valves.

PS, get a little spray foot powder and spray it around under the banjo bolts. Oil that shows up around the front two bolts often ends up being from a small and invisible leak from the oil line banjo fittings. A little foot powder will make the invisible leak visible. Jim

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Thanks Comnoz,
I didnt think the 850's had a breather problem like the 750's did.
It doesn't seem to leak unless im riding in a higher RPM, like +4500
Well today im going to put thread sealant on the #9-10 nuts and re-torque the head.

MS850 said:

I didnt think the 850's had a breather problem like the 750's did.

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Yes they do, particularly at the higher rpm's. You may solve a lot of leak problems with the simple addition of a brake booster valve in the breather hose. Jim

MS850 said:

Well I spoke too soon, rode to work today and found a oil leak coming nuts #9 and 10.
SOB, :evil:

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Not sure if someone already mentioned this but the Commando 850 head is prone to crack in the front between the third and fourth fin (right behind the two front 5/16” nuts at the bottom of the recess). This crack is often caused by over tightening the two front 5/16” nuts (they need only 20 pounds instead of 30 pounds for all the other head fasteners). The problem is that there is little aluminium material from the pushrod tunnel to the recess for the 5/16” nuts.This crack is quite common and for that reason I made a special pressure tool to test 850 heads for that specific crack. I even tried to cure this crack by grinding off all involved front fins, welding the crack, welding back the fins however it lasted only a short period before the crack turned up again. But if anyone does find a cure for this crack I'd really appreciate to learn as I still have about half a dozen of these cracked 850 heads in my workshop.

Good luck,

Constant Trossèl
http://www.hollandnortonworks.eu

Holland Norton Works said:

MS850 said:

Well I spoke too soon, rode to work today and found a oil leak coming nuts #9 and 10.
SOB, :evil:

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Not sure if someone already mentioned this but the Commando 850 head is prone to crack in the front between the third and fourth fin (right behind the two front 5/16” nuts at the bottom of the recess). This crack is often caused by over tightening the two front 5/16” nuts (they need only 20 pounds instead of 30 pounds for all the other head fasteners). The problem is that there is little aluminium material from the pushrod tunnel to the recess for the 5/16” nuts.This crack is quite common and for that reason I made a special pressure tool to test 850 heads for that specific crack. I even tried to cure this crack by grinding off all involved front fins, welding the crack, welding back the fins however it lasted only a short period before the crack turned up again. But if anyone does find a cure for this crack I'd really appreciate to learn as I still have about half a dozen of these cracked 850 heads in my workshop.

Good luck,

Constant Trossèl
http://www.hollandnortonworks.eu

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Egads I hope its not cracked.
thanks for info

MS850 said:

That is why most people install crankcase breather check valves.

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Thanks Comnoz,
I didnt think the 850's had a breather problem like the 750's did.

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The quick and dirty is to install one of these http://www.autozone.com/fittings-and-ho ... umber=true immediately outside of the timing case in the vent line. On my '74, it's the same size as the existing line, so a very short section of hose did the trick. The outlet, however, is smaller, so a new hose will need to be run up to the oil tank port. 'Turns out, the original hose had a reducer next to the tank that just happened to be the same size as the outlet of the check valve. Take out the old hoses and reducer, and both the valve's outlet and tank inlet are now the same. Easy-peasy!
The first one didn't last through the summer, but this latest one has done over six thousand miles. It does make a difference in seepage.

Nathan

Nater_Potater said:

MS850 said:

That is why most people install crankcase breather check valves.

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Thanks Comnoz,
I didnt think the 850's had a breather problem like the 750's did.

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The quick and dirty is to install one of these http://www.autozone.com/fittings-and-ho ... umber=true immediately outside of the timing case in the vent line. On my '74, it's the same size as the existing line, so a very short section of hose did the trick. The outlet, however, is smaller, so a new hose will need to be run up to the oil tank port. 'Turns out, the original hose had a reducer next to the tank that just happened to be the same size as the outlet of the check valve. Take out the old hoses and reducer, and both the valve's outlet and tank inlet are now the same. Easy-peasy!
The first one didn't last through the summer, but this latest one has done over six thousand miles. It does make a difference in seepage.

Nathan

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Ok, please explain why the hose from the timing cover vented to the atmosphere would work better the the hose with check valve.

And also I found the intake rocker cover leaking, its eventually fills a cavity on the top of the head and when it cant hold anymore oil it runs out right where the #9-10 heads are!
I thought the leak from the front push rod openings blew oil back onto the back of the head and on the rocker cover and intake manifold. Maybe the other way around.
I read this scenario, but not sure where. I have a silicone gasket Ill try, and new copper gasket on nut.

MS850 said:

Ok, please explain why the hose from the timing cover vented to the atmosphere would work better the the hose with check valve.

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It doesn't. The hose from the timing cover vented to atmosphere works worse than the check valve. With both pistons rising and falling together, the crankcase can be turned into an 850cc vacuum pump by the use of a check valve. Theoretically, this will keep the crankcase sub-atmosphere, and, hopefully, pull air in through the cracks, rather than pushing oil out.

MS850 said:

And also I found the intake rocker cover leaking, its eventually fills a cavity on the top of the head and when it cant hold anymore oil it runs out right where the #9-10 heads are!
I thought the leak from the front push rod openings blew oil back onto the back of the head and on the rocker cover and intake manifold. Maybe the other way around.
I read this scenario, but not sure where. I have a silicone gasket Ill try, and new copper gasket on nut.

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FWIW I'm chasing down some similar leaks, installed silicone VC gaskets which worked OK except on the primary side exhaust valve cover where a conventional gasket seals better. I also discovered that the flats for the nuts on that that side were not machined parallel to the face and fixed that with an end mill. Ran the Motormite check valve and it definitely reduced leakage but I replaced it with a reed valve from Mikes XS (about $20), from what I've read here they last much longer...anyway there are lots of threads here on that reed valve.

MS850 said:

Ok, please explain why the hose from the timing cover vented to the atmosphere would work better the the hose with check valve.

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Here are some pictures I took several years ago when I was working on an effective breather.
These are scope traces from an absolute pressure sensor installed in the hole where the tach drive had been removed. The engine was running at 3600 rpm on the dyno with a light load.
The sensor converts the pressure to a voltage at real time.
+5 volts is equivalent to 1 bar of pressure
-5 volts is minus 1 bar of pressure
The horizontal center line of the scope is 0 pressure and full screen is +5 to - 5 volts.

Shot one shows a stock open breather from the timing chest on an 850. Note that the average pressure -halfway between peak to peak is above zero and there is a large variation in pressure as the pistons go up and down



Shot two shows what happens with a brake booster valve in the line from the timing chest. Since the check valve lets air out but not back in -there is less air to compress so the pressure swings are smaller and the average pressure is now below the zero pressure line.



Now if you really want to get tricky. Here is a shot of the pressure with a reed valve directly connected to the crankcase and all the holes except one drainback hole plugged between the crankcase and the timing chest.

Jim, the Vincent World needs to hire you away from Norton World!

Glen

worntorn said:

Jim, the Vincent World needs to hire you away from Norton World!

Glen

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Awe, It wouldn't work as well on a v-twin.....