I am pulling my 850 head and cylinders off for the first time and hope to get your advice !

D

DennisMo

VIP MEMBER
Joined
Jun 6, 2023
Messages
365
Country flag
Hello all,

I am fairly certain that I have caused internal damage from overheating the engine. I was caught in creeping traffic on a hot summer's
day for a couple of hours and since then have lots of very visible warm idle engine vented blue blowby gases into the oil tank with
water drops being blown in when cold. And thus milky oil.
It takes 45 minute to an hour's ride on a hot summer's day to revert back to non milky oil. But a short ride. say 30
minutes starting with a cold engine on a summer's day will make oil milky. Without very long rides, the oil blows milky frothy into the tank and
I see buildup. My thought is that the piston rings and/or bore has been compromised.

So I will take it apart and inspect. Can you advise me on the following?

1) Do I actually need the tool to pull the valve rocker shafts out of the head or do they pull out by hand. If tool is needed, do I need to heat the head?

2) Do I actually need the tool to pull the wrist pins out of the pistons or do they tap out at room temperature after removing circlips?

3) Can you tell me what gasket sealant you recommend on the cylinder base gasket that goes between the crankcase and cylinders when reassembling?

4) Some suggest putting a bead of sealant on the head gasket, just around the rocker shaft tunnel. Do you recommend this and if so
what sealant do you suggest? Do you recommend it anywhere else on the head gasket? I will use a composite gasket.

5) After installing a new head gasket, at what mileage do you retorque it and do you retorque it again after that retorque? To retorque, I would loosen one at a time, then tighten in two stages, first to half torque, then to full torque. Then onto next one.

6) Lastly, I have the tools to measure the bore diameter and piston diameter as well as feeler gauges to measure piston to cylinder wall gap.
But my knowledge is based on British classic car engines only. I imagine much of that translates, but I would appreciate if someone might walk me through how they measure it all. My hope is that I find that only the piston rings are compromised from the overheating and that new rings and hone will solve all. ButI am a realist. I know I might find scored bores etc....

A huge thanks to all of you.
I have been on the forum for a few years since I got my 850 and am very appreciative of the advice I have received. I have redone (thus learned) about everything on my bike except the engine and transmission. I picked up a spare transmission and one day will pull it apart to learn. But for now, it is the engine top end I will be learning about.
Thanks again. You guys are great

Dennis
Vancouver
 
DennisMo said:
1) Do I actually need the tool to pull the valve rocker shafts out of the head or do they pull out by hand. If tool is needed, do I need to heat the head?
Click to expand...
They should be tight in the head so you should heat the head and use the tool to pull the rocker spindles out but then you don't need to remove them to remove the head.

DennisMo said:
DennisMo said:
2) Do I actually need the tool to pull the wrist pins out of the pistons or do they tap out at room temperature after removing circlips?
Click to expand...
Click to expand...

No but it might be better to warm the pistons first if the pins are tight.
 
DennisMo said:
Hello all,

I am fairly certain that I have caused internal damage from overheating the engine. I was caught in creeping traffic on a hot summer's
day for a couple of hours and since then have lots of very visible warm idle engine vented blue blowby gases into the oil tank with
water drops being blown in when cold. And thus milky oil.
It takes 45 minute to an hour's ride on a hot summer's day to revert back to non milky oil. But a short ride. say 30
minutes starting with a cold engine on a summer's day will make oil milky. Without very long rides, the oil blows milky frothy into the tank and
I see buildup. My thought is that the piston rings and/or bore has been compromised.

So I will take it apart and inspect. Can you advise me on the following?

1) Do I actually need the tool to pull the valve rocker shafts out of the head or do they pull out by hand. If tool is needed, do I need to heat the head?

2) Do I actually need the tool to pull the wrist pins out of the pistons or do they tap out at room temperature after removing circlips?

3) Can you tell me what gasket sealant you recommend on the cylinder base gasket that goes between the crankcase and cylinders when reassembling?

4) Some suggest putting a bead of sealant on the head gasket, just around the rocker shaft tunnel. Do you recommend this and if so
what sealant do you suggest? Do you recommend it anywhere else on the head gasket? I will use a composite gasket.

5) After installing a new head gasket, at what mileage do you retorque it and do you retorque it again after that retorque? To retorque, I would loosen one at a time, then tighten in two stages, first to half torque, then to full torque.

6) Lastly, I have the tools to measure the bore diameter and piston diameter as well as feeler gauges to measure piston to cylinder wall gap.
But my knowledge is based on British classic car engines only. I imagine much of that translates, but I would appreciate if someone might walk me through how they measure it all. My hope is that I find that only the piston rings are compromised from the overheating and that new rings and hone will solve all. ButI am a realist. I know I might find scored bores etc....

A huge thanks to all of you.
I have been on the forum for a few years since I got my 850 and am very appreciative of the advice I have received. I have redone (thus learned) about everything on my bike except the engine and transmission. I picked up a spare transmission and one day will pull it apart to learn. But for now, it is the engine top end I will be learning about.
Thanks again. You guys are great

Dennis
Vancouver
Click to expand...
1) NEVER pull the rocker spindles without heating. A tool makes it easier but a bolt will work.
2) Just warm the pistons, no tool needed for the wrist pins.
3) None!
4) IMHO, and on the advice of AN, a thin smear of silicone around the pushrod tunnels but not on the fire ring. Thin smear around the oil drain hole. Put some around the two 5/16" studs sticking up from the cylinders. You will find LOTs of opinions on this one!!!
5) Retorque soon after starting, then probably around 500 miles and 1000 miles. No loosening and tightening. Do it in the correct order.
6) I use 0.004" piston skirt clearance - check front to back but firs you must know if the bore is tapered. Taper is what is really important. If the bottom of the bore is significantly larger than the top, it's time for a bore. I the workshop manual says .005" max - to me, bore at .004" or more. If it's tapers .004" and you change for skirt clearance at the bottom of .004 you will have zero at the top and will seize! Edit: See the next two posts - I did not say this clearly at all!
 
Last edited:
hhh said:
I think you meant: "if the top is larger than the bottom."
Click to expand...
Yes, and really the best way to say it is the difference at the top and bottom of the ring swept area and unswept area since it might stop confusion between cylinder bore and piston skirt and the unworn part below the ring swept area. In the end, if the cylinders are tapered - it's not good if too much!

1766779819088.png
 
Last edited:
DennisMo said:
Hello all,

I am fairly certain that I have caused internal damage from overheating the engine. I was caught in creeping traffic on a hot summer's
day for a couple of hours and since then have lots of very visible warm idle engine vented blue blowby gases into the oil tank with
water drops being blown in when cold. And thus milky oil.
It takes 45 minute to an hour's ride on a hot summer's day to revert back to non milky oil. But a short ride. say 30
minutes starting with a cold engine on a summer's day will make oil milky. Without very long rides, the oil blows milky frothy into the tank and
I see buildup. My thought is that the piston rings and/or bore has been compromised.



Dennis
Vancouver
Click to expand...
Thinking more about this. Bad rings or bore won't cause water. Sounds like condensation. Where are you seeing the blue gases going into the oil tank? Do you have blue smoke out the exhaust? Milky oil is usually homogenized oil and water, but can be homogenized air and water but it's less white. What do you mean by "I see buildup".

Lugging Commandos is a really bad idea and you might have a problem, but I would figure out where the water is coming from first and I would do a compression test before taking it apart. You might have one or two bad intake valve seals - especially if you see blue smoke out the exhaust.
 
1, No
2, No
5, retorque after first thermal cycle, engine cold, then 50 miles, 100 miles, 500, 1000 always engine cold
6, To accurately measure a cylinder bore you really need an outside micrometer of the correct range and a bore comparitor. The use of these two tools makes it easy to check how worn/tapered/oval the cylinder bore is. Google how to use such tools. Just using a digital vernier gauge or similar will not tell you what the bore is like halfway down the bore..
Buy and read the workshop manual, almost every question is covered in the manual.
 
I see lots of milky oil froth where the crankcase breather vents into the oil tank.
When cold, the oil tank vent to atmosphere spits out a lot of water.
There is a lot of a blue blowby coming out off the oil tank vent (which goes to atmosphere) when the bike is fully warmed up.
I can get rid of all the froth in the oil by going on a very long ride which means hot oil.

But if I then park the bike with oil clear of white froth due to a long run, I will get the froth again after the next run from cold start
if the run is short

I had none of this for the first couple of years of ownership and the froth only started after I think I cooked it by being stuck in summer heat traffic stop and go for 2 hours.
 
I changed the oil three times and tried two new brands.
When I changed it, it would run clear for the first run and then for the second run it would be back at the white oil froth unless I went on a long run to boil off the water.
 
DennisMo said:
Greg,
When you say warm the pistons do you mean very, very gently with a propane torch?? (and taking much care!)
Dennis
Click to expand...
I use a propane torch or a heat gun. They don't need to be very hot in most cases. Just warm them and try, if they don't move warm some more.
 
Warm the engine by riding several miles. Pull the plugs and check compression. If low then squirt oil into cylinders and check again. The engine does not produce water, so it might be airborne moisture condensing. I have experienced milky oil with engines that have sat outside for a long time. Several oil changes while hot rectifies the issue. Aluminium engine cases will sweat with temp changes. If I turn my tank breather downwards on a cool morning drips of condensed H20 will drip out. I use a vw brake one way valve as an engine cc breather. Is your case well vented?
My compression is 95-95. Seems low, but plenty of power. Works for me. Do you live in a very humid area?
 
DennisMo said:
I changed the oil three times and tried two new brands.
When I changed it, it would run clear for the first run and then for the second run it would be back at the white oil froth unless I went on a long run to boil off the water.
Click to expand...
Has the oil tank been flushed and cleaned?
Or old school term, 'Boiled out'.
 
Could be as simple as cooked inlet guide seals letting oil into the combustion chamber. Worn rings is another, you should be getting through 2 sets of rings before a rebore is needed.
 
Back
Top