Vacuum Issue:
1976 Triumph TR6
I apologize for the long post leading to a simple question, I just hope to answer all the queries in one go and get an answer.
This issue is new, head done and cam just replaced by 'other', am finding many deficiencies in work unfortunately; including the distributor drive gear was in 180. (The crazy twisted installation of the distributor and offset wiring installation was the first clue.)
I corrected the distributor drive gear as per the book, reinstalled the distributor, the plug wires in the proper orientation, and the distributor looks correct with the dizzy at #1. The distributor is Vacuum retard with points.
The car previously timed right on the numbers, vacuum at 18 at idle and ran well.
Current set up:Static timing: 10deg BTDC
Plugs: 0.025”
Rockers: 0.010” cold
When running:
Idle: 750rpm
Dwell 37deg (want 36)
Dynamic: 4deg BTDC (want 4deg ATDC) (remember... vacuum retard)
Vacuum: 8.5-9.5 buzzing needle (should be 18)
Distributor Vacuum removed: Dynamic 14 deg BTDC, 1000rpm
I have checked all vacuum connections best I can, and tried this with the canister and Brake master cylinder plugged. Same.
also: for some reason, on acceleration, vacuum increases (?) to 18 at about 2500rpm
Suspect:
Lack of vacuum is causing issues with the vacuum retarded timing as it is not advancing the distributor enough. I suspect proper vacuum will rectify timing, but will not know until it is resolved.
The low vacuum indicated either a manifold leak or valve timing… a manifold leak should present itself with a steady vacuum gauge needle, the constant frequency(buzzing) of the vacuum gauge needle suggests it is a problem with the cylinders, all cylinders, ie how they are pulling air, the valve timing.
Next check:
Suspecting cam installation…. I turned the crank till #6 valves, 11 & 12 we off the cam and had 0.010” clearance. I then attached indicators to the rockers (2’ long stiff wires) and lined up the ends of the wire to each other precisely (holding the rocker clearance out). I then rotated the crank until the two indicators we passing each other on the rock, and stopped in the direction of engine rotation when they were perfectly aligned. (The two foot indicators providing precision because of their motion at the tips… about 6”.) As triumph cams are symmetrical, this indicated Cam TDC. At this point I read the degrees on the crank pulley.
The crank is 11deg BTDC. Basic 2:1 math says that when the crank continues to TDC, the Cam will be 5.5deg ATDC. Not a tooth out… but perhaps the wrong bolt holes on the cam gear.
Would this cam advance cause my vacuum issue?
I want to get the car back to spec.
Please advise.
Stephen
1976 Triumph TR6
I apologize for the long post leading to a simple question, I just hope to answer all the queries in one go and get an answer.
This issue is new, head done and cam just replaced by 'other', am finding many deficiencies in work unfortunately; including the distributor drive gear was in 180. (The crazy twisted installation of the distributor and offset wiring installation was the first clue.)
I corrected the distributor drive gear as per the book, reinstalled the distributor, the plug wires in the proper orientation, and the distributor looks correct with the dizzy at #1. The distributor is Vacuum retard with points.
The car previously timed right on the numbers, vacuum at 18 at idle and ran well.
Current set up:Static timing: 10deg BTDC
Plugs: 0.025”
Rockers: 0.010” cold
When running:
Idle: 750rpm
Dwell 37deg (want 36)
Dynamic: 4deg BTDC (want 4deg ATDC) (remember... vacuum retard)
Vacuum: 8.5-9.5 buzzing needle (should be 18)
Distributor Vacuum removed: Dynamic 14 deg BTDC, 1000rpm
I have checked all vacuum connections best I can, and tried this with the canister and Brake master cylinder plugged. Same.
also: for some reason, on acceleration, vacuum increases (?) to 18 at about 2500rpm
Suspect:
Lack of vacuum is causing issues with the vacuum retarded timing as it is not advancing the distributor enough. I suspect proper vacuum will rectify timing, but will not know until it is resolved.
The low vacuum indicated either a manifold leak or valve timing… a manifold leak should present itself with a steady vacuum gauge needle, the constant frequency(buzzing) of the vacuum gauge needle suggests it is a problem with the cylinders, all cylinders, ie how they are pulling air, the valve timing.
Next check:
Suspecting cam installation…. I turned the crank till #6 valves, 11 & 12 we off the cam and had 0.010” clearance. I then attached indicators to the rockers (2’ long stiff wires) and lined up the ends of the wire to each other precisely (holding the rocker clearance out). I then rotated the crank until the two indicators we passing each other on the rock, and stopped in the direction of engine rotation when they were perfectly aligned. (The two foot indicators providing precision because of their motion at the tips… about 6”.) As triumph cams are symmetrical, this indicated Cam TDC. At this point I read the degrees on the crank pulley.
The crank is 11deg BTDC. Basic 2:1 math says that when the crank continues to TDC, the Cam will be 5.5deg ATDC. Not a tooth out… but perhaps the wrong bolt holes on the cam gear.
Would this cam advance cause my vacuum issue?
I want to get the car back to spec.
Please advise.
Stephen
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