Experience Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.
Organizations Associate member SAE
EAA member
Publications Import Car magazine
Education/Credentials ASE Master Auto with L-1 certification up to 2000
I've checked the following:
Dwell 35
Timing 4 ATDC
Vacuum 14 hg and steady (brake booster disconnected & plugged gauge connected to anti-run valve port)
Compression: 90# all cylinders w/ throttle plates closed.
Plugs gapped at .025
Idle set at 800rpm
Carb mixture setting 1 turn down from full rich.
Carb's are in sync.
Car missing at all speeds, but not a steady miss. Seems fine under load. Any Ideas? Thanks Craig Jones
ANSWER: HI Craig,
You are giving me confusing info, "90 PSI compression test with the throttles closed is useless info. (not much air in= not much compression)
and I don't understand "Carb mixture setting 1 turn down from full rich".
You need to hold the throttle open to do a compression test since almost no piston gas engine will run below 100 PSI.
The method to set the mixture is to lift the spring loaded pin just under the side of the each carb and note the response, then adjust the mixture as per the response. If the engine speeds up and stays fast the OTHER carb is too rich, if the engine dies you either didn't get them in sync or the OTHER carb is too lean. When the OTHER carb is correct the engine will drop off and run slow and sound like a two cylinder engine running slow. It is advisable to rev the engine a little between each test and adjustment. (most books don't tell you that you are checking the other carb.)
Howard
---------- FOLLOW-UP ----------
QUESTION: Thanks for the quick response.
I re-did the compression test with the throttles open and the results are as follows #1-120#, #2-120#, #3-110#, #4-120#, #5-90#, #6-120#... Looks like rings are in order. Know any recommended mechanics in Washington?
Thanks Craig
ANSWER: Craig, you should either have a leak-down test done to get a better idea as to weather the low cylinder (#5) is low because of a ring problem or a valve problem.
An additional "Wet" test is in order. You can do this by just squirt about 4 or 5 squirts of engine oil in a plug hole and do another compression test on each cylinder. If you see a lot more than 10% to 15% higher readings then there is a good chance it is a ring problem. If the Wet test are not more than the 15% then it is a valve problem and you can just do a head repair.
Sorry, I'm in Tenn. and I don't know anyone in Wash.
Howard
---------- FOLLOW-UP ----------
QUESTION: I Did a wet test last night and all cylinders improved to appox 150#. Can a ring job be done with the engine installed? Another item I'm curious about is the RPM rises about 100 when I use the unisyn on the rear carb but stays constant on the front. Any idea why?
Thanks Craig
Answer If the RPM raises when you put the Unisyn gauge over the intake of the rear carb it is just an indication of a possible intake leak or that carb is quit lean.
I have never tried to do a ring job in the car on a TR-6. It is very difficult to deglaze the cylinder walls without getting the residue down on the crank and bearings. I did deglaze a friend's MGA in his own garage once by stuffing rags at the bottom of the bore to catch everything but we were not allowed to do it in the dealership. Look at getting the pan off. If you can get the pan off you can do it in the car, just be sure to stuff rags in at the bottom when you deglaze the walls. Wash the walls with soap and water after deglazing and oil right away. There MUST not be any ridge at the top of the bore. If there is, you are in great danger of the new rings hitting the ridge and breaking the top ring and the piston. The old ring would have the top edge worn down to match the edge of the groove but the new sharp edge of the new ring will catch the edge of the groove and break the ring land down between the top and second ring. If you do have a ridge at the top of the bore, you can use a ridge reamer to remove the ridge and then use a hone to smooth the transition out. This is not an acceptable practice in a shop but on your own car it can be used to get some extended life out of an engine without boring all the cylinders and putting in oversized pistons.
Good luck and let me know how it turns out.
Howard
