T150v head scratcher

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
Bolted up my T150v after overhaul. All stock but for the 850 cylinders. I've assembled several over the years so no surprises.
Well not this time: When I attempted to torch it off, I got instand pooping like you would hear with a car with a blown exhaust
gasket. All three cylinders get hot exhaust pipe. Never ran it for more than 10 seconds. It seems to be blowing back through
the carbs. One plug is clean one is mildly rich and one is black. Ten seconds! Have carefully checked static timing (TriSpark
remote black box type) on each cylinder. Carbs stripped and cleaned free passage in all the tiny ports. Valves lashed a thou
loose. Valve timing per marks. Did a bypass compression test all cylinders are 77/80 with only the faintest his in the intakes with
the carbs removed.
The bike ran flawlessly before I pulled it down, it just leaked at the cases. Of course I found the centre mains unhappy so
they were replaced.
But I am puzzled. What on earth is going on?
 

Carl H

VIP MEMBER
Joined
Dec 13, 2017
Messages
103
Country flag
Best guess Cam timing Usually leak down is caused by the rings only in a new engine job , If the valve job was done properly, they should not be leaking when they are on the compression stroke at TDC as the valve is fully closed. I don't know any thing about Tri sparks, But is it all wired properly with good voltage going to it?
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
I too felt it was cam timing but rather unlikely. Time to check it carefully. It has brand new pistons and rings.
3 pounds off is pretty small.
Hate to pull the head off again but you don't know until you know and you have to be sure.

Coils show 3.9 ohms, Lucas calls for 3.2 to 3.8 I think.
Bike ran fine before I took it down and no trouble starting.
 

storm42

VIP MEMBER
Joined
Jul 20, 2011
Messages
945
Country flag
Could two of the plug leads or coil feed wires have been swapped over, the ones with the rich looking plugs?
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
TriSpark is cylinder specific not wasted spark so each cylinder was checked for spark at the "B" mark on the alternator rotor.
Plug sparked laid on the head at the correct time.
I sure wish I could find a stupid mistake!
 

storm42

VIP MEMBER
Joined
Jul 20, 2011
Messages
945
Country flag
That can be the problem with mistakes, they are only stupid when you do find them, up to that point it all makes sense.

So , if it is popping back into the air box, then sticking valves, inlet cam timing or ignition, sorry not very helpful.
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
There are times when you are flummoxed that you simply start from the beginning and proceed again.
This may be one of them.
 

Fast Eddie

VIP MEMBER
Joined
Oct 4, 2013
Messages
14,431
Country flag
As you’re a Norton bloke, you haven’t set the Tri Spark timing by rotating it the wrong way?

Doing that puts the timing out several degrees.

No prizes for guessing how I know that :rolleyes:
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
I put the bike in 5th gear, remove the plugs, lay them on the head to ground them, bump the
rear wheel FORWARD ( :) ) and watch for the "B" mark to line up with the pointer and the plug
to spark. If it is off a bit I adjust the plate (Advance is marked with an arrow on the plate).
Then I back off the rear wheel a bit and rebump forward. When the spark pops at the plug I check the pointer etc.
It is exactly on the mark and on the correct cylinder. I did this with each cylinder.
 

storm42

VIP MEMBER
Joined
Jul 20, 2011
Messages
945
Country flag
I am not familiar with the Trispark and therefore the B mark, is there a B mark for each cylinder? And if there is, are they lining up for the cylinder that is coming up to TDC?
I ask because I had something similar with a T160 and it was the feed wires to the coils on wrong.
On another totally unhelpful note, you have spurred me on to getting my T150 on the bench to sort the clutch and an oil leak.
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
The "B" mark is the standard timing mark on the rotor, later triples, the "A" mark used for earlier. It depends on which crankshaft you have.
If you time it the way I have all the wires are in place just as you would have them if you ran it. So you are sure about all the locations. Worse, the bike ran fine previously and I have done naught to the electrics anywhere.
What gauls me is that I am not a novice to triples or bikes in general. This is quite embarrassing actually.
 

Fast Eddie

VIP MEMBER
Joined
Oct 4, 2013
Messages
14,431
Country flag
Doesn’t the black box have an LED?

The Tri Spark classic has an LED and I get the timing absolutely cock on using that.
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
The newer type yes, easy, the remote black box not so as the LED is INSIDE the bloody box!
Watching the plug is easier.
 

Fast Eddie

VIP MEMBER
Joined
Oct 4, 2013
Messages
14,431
Country flag
Ok, seems we’re clutching at straws now...

You sure you got fresh juice?

Clean and good plugs (after all, those triples burn more oil than fuel right) ??

Out of interest, what kinda 850 kit you running ?
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
After some thinking: If the tappets are at 6 thou at 38 BTDC the only way a kick back into the carb
can happen is most likely a leaking intake valve. I pulled the head. No hung valves, no other disasters
seen. Two of the seats show tiny pitting. They should be cleaned up, the valves are all good as are the
guides. Two pistons were covered in black oily grease like stuff but they wiped clean with just a rag.
All I can think of is that we have a carb problem so I shall strip the carbs again and examine hoping to
find whatever I have missed. They are low mileage premiers. Did notice that the coils have 4 ohm resistance
when they should have 3.8 I think. TriSpark coils are 3.6. Spark, static, is not that impressive.
Jugs are from Neil Beadling .
 

Carl H

VIP MEMBER
Joined
Dec 13, 2017
Messages
103
Country flag
Unless you heavily oiled up the rings and pistons when you assembled it, That would concern me as to trouble with rings and bores, Providing it isn't head or valve guide or gasket related.
 

Fast Eddie

VIP MEMBER
Joined
Oct 4, 2013
Messages
14,431
Country flag
Neils jugs are the best there is, there’ll be nowt wrong with them.

If things were that oily inside it kinda sounds like perfect fouled plugs territory ...?
 

Onder

VIP MEMBER
Joined
May 11, 2010
Messages
2,803
Country flag
This story is on hold for a while until I can get back to work on it. I will follow it all up in the future. Nothing worse than a thread about a problem where the solution is never mentioned.
 
Top