Tiger 750 Breather

[ManInTheJar]

I have been told that my recently acquired TR7 has a belt primary drive of unknown origin. I certainly sounds quiet enough from the chaincase so I have no reason to doubt this. The question is, has the chaincase been sealed to allow the belt to run dry? I can't detect any obvious pressure, pulsing, fumes etc coming out the chaincase breather, is this a sign that the chaincase has been sealed off or is that normal?

 

[griffindog]

If it is belt primary it would be sealed, dont wont oil on a belt.

 

[ManInTheJar]

If it is belt primary it would be sealed, dont wont oil on a belt.

I'm guessing that's the case, just wanted to see if I could check without stripping it down. Also if the chaincase is sealed then I will probably need to think about an alternative location for a breather.

 

[griffindog]

If it is belt primary it would be sealed, dont wont oil on a belt.

My 74 Bonneville has a fill cap at the top of the primary you can look into there and drop a stick in to make sure no oil. About the Breather they sell a small filter type breather or just leave the hose on

 

[Rudie]

If it is belt primary it would be sealed, dont wont oil on a belt.

Incorrect. Many belt materials are quite capable of running in oil without problems.

has the chaincase been sealed

If it has, there must be a crankcase vent elsewhere; the crankcase volume changes by approximately 750 cc every crankshaft revolution so this vent will be obvious.

Also as standard, the frame vents/drains into the standard crankcase/primary vent hose and then into the chaincase; as the drain was for oil, if the primary has been sealed from the crankcase, again, the drain must be elsewhere into the crankcase.

 

[griffindog]

Incorrect. Many belt materials are quite capable of running in oil without problems.


If it has, there must be a crankcase vent elsewhere; the crankcase volume changes by approximately 750 cc every crankshaft revolution so this vent will be obvious.

Also as standard, the frame vents/drains into the standard crankcase/primary vent hose and then into the chaincase; as the drain was for oil, if the primary has been sealed from the crankcase, again, the drain must be elsewhere into the crankcase.

 

[griffindog]

Rudy is correct sorry about that

 

[speedrattle]

you can shine a light down the uppermost fill hole in the primary to see whether its a belt or a chain in there.

pop off the front rotor inspection plate and stick a wire down into the bottom of the chaincase to see whether it comes back out wet with oil.

like rudie says, belts can be wet or dry, depending. if its dry in there, you must have a crankcase breather somewhere. look for a hose off the crankshaft timing plug below the intake pushrod tube, an exterior hose off the timing cover, or a hose off the front triangular part of the crankcases, at the front motor mount.

 

[ManInTheJar]

Finally got around to checking out the primary chaincase. There is definitely a belt which feels in good condition, it looks to be a reddish brown in colour. Using some copper wire as a dipstick suggest the chain case is dry and as I said in an earlier post there is no pressure/pulsing/fumes when placing a hand over the end of the breather pipe with the engine running - it all points to the crankcase being sealed rendering the breather ineffective.

A visual search suggests there is no breather connected to any other point at obvious locations like the timing hole, timing cover, front engine mount to cylinder head. The most obvious method of rectifying this would be something like the MAP Cycle kit but not only does it show out of stock when added to the basket but I would need a mortgage to pay the shipping cost.

My next question is are there alternative easily obtainable (UK) kits available or a source for a hose adaptor which would fit in the timing hole and a suitable SAI/Check Valve. I believe the hole is a UNC thread but will confirm when I check the timing.

 

[speedrattle]

sealing the crankcase without a vent will pressurize it whenever the pistons descend. that can cause oil leaks anywhere the pressure can squeeze out. its odd that someone would install a belt without addressing that.

i have installed breathers by drilling the front crankcase, but that requires motor disassembly. i also install breathers very easily by drilling holes in the rocker inspection covers, tapping and screwing in a stub for a hose. this lets the motor breathe up and down through the drain holes in the tappet guide blocks. theyre small, but work, and are much better than nothing.

putting a breather on the timing hole under the intake pushrod tube causes difficulties because it collects oil thrown out by the crank. still, its the easiest way to go, and if you lead the vent line vertically to the frame spine might work fine. i wouldnt put a valve on it because that would retard oil drain back. just make it as long and as large an ID as you can.

 

[Rudie]

sealing the crankcase without a vent will pressurize it whenever the pistons descend. that can cause oil leaks anywhere the pressure can squeeze out. its odd that someone would install a belt without addressing that.

+1.

breather on the timing hole
oil drain back. just make it
as large an ID as you can.

Something that will be made more difficult by the restricted space directly above the timing hole between the cylinder head and the single carb manifold.

 

[speedrattle]

yes, i can see that that could be a problem.

people commonly just drill a hole in the timing cover up near the top, install a 90-degree hose barb, and then run a long open tube to the rear. the longer and bigger tbe better, because the idea is to have the inner volume more than the 750cc going up and down inside. or you can fit a filter.

the down side of that is the hose and fitting are pretty ugly and that can be important on an original-looking machine

 

[ManInTheJar]

+1.


Something that will be made more difficult by the restricted space directly above the timing hole between the cylinder head and the single carb manifold.

I have a few ideas running through my head. All are based on avoiding a strip down/structural mods and trying to get a solution which is reasonably discrete but effective. Maybe a combination of some of these would work.

1. Fit a MapCycle kit or similar
2. Timing hole breather - insert some stainless gauze/wool close to the start of the breather hose to filter out larger oil droplets.
3. Timing hole breather- Use an inverted sealed catch can (500cc ?) under the tank, connected to the breather hose via a tee piece to act as a sort of plenum chamber.
4. Timing hole breather- Use an adaptor to run a section of larger diameter breather hose. By my calculations roughly 18" of 1" ID hose would be equivalent to 750cc.
5. Timing hole breather- fit an SAI a good distance from the start of the breather (under the tank or seat?) With a run in the hose back to the timing hole to let excess oil drain back. Mike's XS sell a Heiden Tuning SAI which they suggest modifying with a 1.5mm hole between the inlet and outlet.

I am open to other suggestions though.

 

[speedrattle]

^^^heres a simple hose fitting on the front of a T120. for this to work, this triangular cavity is drilled into the crankcase with drain holes and then filled with a ball of stainless steel mesh. a hose runs to the rear and fits into an open top plastc catch bottle

 

[ManInTheJar]

**UPDATE**

I have removed the chaincase cover to maintain the clutch and fit a 3 phase alternator. There was a light film of oil everywhere and a small pool of oil lying in the bottom. The three level holes are clear (checked with copper wire) and on removing the rotor and primary pully I found that there was NO seal on the crank bearing.

So basically the engine has been breathing using the stock arrangement, albeit with partially collapsed breather tube. It does not look like the chaincase was primed so presumably the minute quantity of oil there had come from the vapour passing through the crank bearing. The belt drive appears to be a polyurethane type material, not rubber, and is in great condition.

The clutch has a Devimead alloy cover with needle thrust bearing, similar to SRM.

Once I have refurbished the clutch and upgraded the alternator I intend to put it back together with the breathing arrangement "as found" as this seems to have worked OK with the belt and clutch ("if it isn't broken don't fix it". ). The only change will be a new, unobstructed, breather tube.

 

[speedrattle]

the three little holes serve only an aspirational purpose in most applications. all the oil will mist back and forth through the drive side main bearing. the level goes up and down in the chaincase as rpm and engine use dictate.

on breathing, if this is a TR7 doesnt it retain th estock breather at the top of the chaincase? there will be a tube leading back under the rear mudguard and another coming in from under the upper spine tube. if that is intact, then the breathing should be adequate, if the drive side seal is left out, as designed.