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Question: QUESTION: I have a main shaft that is bad in my gearbox and am looking at replacing it. Will any of the later model gear boxes other than the 62-70 group work ? Other than victoria british do you have any supplier recommendations ?

The only way you will know what other boxes will have the same mainshaft is to check with a parts supplier for the same part number. You might try Moss Motors, The Roadster Factory and Engel Imports. They all have websites.

QUESTION: I am sorry I wasn't clear with my question, Since the mainshaft is bad I was think of just changing out the entire gearbox with another and wondered if any of the other year models after '70 would work.

3.Measure from the front of the bell housing to the shift lever and to the rear flange for the driveshaft. And measure the bolt pattern. (I think they were all the same) and finally look at the trans mounts. (don't remember if they were all the same or not.

Over the years and from when I use to race motorcycles on flat tracks in the AMA I learned a little about cam design. (just enough to get myself into trouble) I started when I was about 16 or 17 years old when I read a book that covered cam profiles. My first attempt was humorous, (read about it in my web site)

Later I tried a cam profile in a Triumph that had a wider duration on both intake and exhaust cams but no higher lift and not much change in overlap. I found it developed a good more horse power but ONLY at very high RPM. I raced that bike on several TT tracks and found it to be lacking mid range torque so when I raced a smaller 500cc bike on flat track I had a cam grinder pick a profile that would give me high torque from mid range up. I raced a 250cc bike at a United States M/C event at Daytona with a much higher RPM cam and I was able to time trial 4th fastest of about 150 bikes that were entered. I went into sports cars later and built many high performance engines for a wide range of sports cars.

My point is that I found that first you must decide what you are going to use the car for. Auto Cross, SCCA, drag racing or a street rod. Then you need to decide how big a pile of money are you going to dump into this engine. And what and how far are you going to modify that engine. Then you should approach a cam grinder /manufacture and ask them what profile they have to match what you want to do. For example a road race (SCCA or such) cam may be useless in an Auto Cross or dirt track.

That is all I can tell you of what I learned about cam profiles. The ONLY useful advice you will get from anyone will be from someone with the exact same engine you have and doing the exact same use as you are and someone who won't lie to you and is successful with theirs.

Question: Thanks for your response. Actually I've been approaching it in much the way that you say but the full history would take many pages, I gave you the short version.

Ignition timing. In the brief time when it was running properly I set it to 12 degrees BTDC with my ancient timing light, as old as the car, it's just a neon tube which is plugged in series with a plug lead. It lights for as long as there's HT current (so the timing marks blur in the direction of rotation and you have to time to the trailing edge). But it does show HT current.

Spark. Jumps about 1/2" between the lead and the plug if it has to. When it's not running properly it needs to be revved at up to 2500 rpm just to keep going - that varies, it started today at about 1000 rpm and got worse - and if you let the revs fall it slows and stops (you can sometimes get it back by blipping the throttle, see mixture). I'm sure it's intermittently not firing at speed and steadily not firing when it stalls. It's obvious that the brightness of the timing light varies, bright when it's firing properly and dim when it's not. My reasoning goes: if there's a flash there's some current, the plugs are newish and clean so there must be a spark. I seem to remember from way back that when the mixture fires the spark voltage drops so the spark current will keep on longer, hence the brighter flash. BICBW.

Mixture. It certainly sounds weak, popping and banging in the exhaust and occasionally spitting back throuh the carbs (the spit back doesn't smell of fuel much though). WD40 in the carbs made almost no difference - the behaviour is pretty random so it's difficult to tell - and I'm pondering something I could use to spray fuel into the inlets. In the meantime i've tweaked the float to get the level in the chambers as high as possible (the jets aren't easily adjustable, they're pressed into place and I don't want to disturb them because, after all, it was right). That helped a bit.

There's only one bleed into the manifold, the emission control valve which sucks oil vapour from the crankcase. I've taken it off and blocked the hole in the past, it didn't make a lot of difference. There is a bimetallic strip controlled bypass to the the venturi which was sticky but I've fixed that (I think)

Answer: Your carbs don't have the 3mm Allen adjustment down in the bottom of the oil reservoir? What happens when you slowly cup your hand over one carb at a time when it is running poorly? Have you looked at the decel valve (3 screws close to the throttle shaft? Every one I looked at in the last 10 years were bad and the diaphragm was so hard the valve couldn't move and when it did it stayed where it was open or closed. It was just for emission control on decel so I run the adjustment so as to force the valve closed but first you need to clean the valve and it's seat. This would not effect mixture but could cause a high and low idle at times. Are the butterfly screws tight and the butterfly seated correctly? Has this got the coolant operated choke or manual?

Question: GT6 1971, sat in the garage for 25 years, now much restored. When I picked it up from the restorer the engine was a bit rough (and noisy because the exhaust pipe contacted the chassis) but it ran. But when I thought I'd got it reasonable it ran OK for a few miles then wouldn't idle.

Since then it's had new coil, ballast resistor, I've stripped down the carbs, reground the valves (cause of the roughness I think) and it still won't idle below 2000 - 3000 rpm, much popping in the exhaust (sounds like weak mixture to me) - except that after some particularly alarming bangs in the exhaust it started to run perfectly. Idled in the garage happily for ?an hour? but 1/2 a mile up the road it went back to 2500 rpm min.

Your symptoms don't pin point the problem. When I was working in dealerships and shops I learned not to target any particular part when I received a car to work on like yours. I used a systematic method of diagnosis which never failed to find a problem and most of the time I was serprised what it was.

I always start with the basics, Compression, fire and fuel is all an engine needs to run with conditions on each, Enough compression (you got that out of the way, 130 to 140 should run fine, Was that done with throttle wide open? If not do it again.) Fuel needs to be available to the combustion chamber and roughly in the correct % with air.

Since compression is not an issue Fire and Fuel are. A firm rule is to do all testing while it is in it's bad made. Testing a car while it is running good is like asking your doctor. "Hay!Doc. my arm use to hurt, it feels fine now, what was wrong with it?"

Checking fire is not hard even if you don't have a scope. When it is in it's bad running mode take a pair of insulated pliers and pull one plug wire off while it is idling and let the spark jump to the plug (not in the sun light) the spark should easily jump a 1/4 inch and be blue in color and be thick (pensile lead size) This just is a rough test of the power of the spark. Now if that is ok set the timing to factory specs. Most specs are set static anyway. This may have to be done when it runs good because you can't set the timing at 2000 RPM. (if you are using a timing light) Now, put a timing light on it and rev it to 2000 RPM and note the amount of advance. Get it into it's failing mode and look at the timing with the timing light. if it is about the same as it was when it was running correctly proceed to Fuel.

For any engine to go from below 1000 RPM up to 2000 to 3000 RPM it MUST receive air from somewhere. If the mixture were to go rich when at idle it would slow down and stumble. So get it in it's failed mode and start pinching off all vacuum hoses (don't forget the vacuum brake booster) Also lift up and push down on the carbs them selves and while it is idling fast. Then cup your hand over the intake of each carb one at a time to try to isolate the problem to one or the other carb.

When testing for fuel you just need to know if it is lean or rich. There are several ways to test this. When it is idling too fast spray some WD-40 into each carb and note the change. If it slows the engine down you have a problem in the carb. If it speeds up and maybe even smoothes out a little it is a vacuum leak.

Question: QUESTION: My door will not stay open and it appears my door check arm no longer has a check arm clip. I need to replace it, but it appears to be riveted on to the check arm. How do I remove the door? Do I need to use a dremel and cut the riveted pin off? Thanks.

yes, you have to drill out the rivet on the check strap to remove the door. Mark around the hinge where it mounts to the body so realignment is easier when you put it back on then remove the bolts holding the hinge to the body.

Question: i know this is sort of outside your area of expertise but would like to see if you may be able to help anyways. i recently was given a 1969 mk3 that had been in storage for 8 years. im trying to change the differential oil and i cant find the drain valve. i know its supposed to be very visible on the bottom of the differential (at least according to the pictures in shop manuals). from what i can see there is a filler valve but not a drain valve obviously im missing something. if you could shed some light on this i would really appreciate it.

Answer: If it does not have a drain plug try removing the bottom bolt holding the third member (sometimes called a "Chunk") to the axle housing, I believe it is drilled all the way through so oil should drain out.

Question: I have a '73 GT6 with a '71 TR6 2.5L engine. It's got dual 175 CD-2 Stromberg carbs. When I run the engine, the exhaust spits out oil and it seems like theres an awful lot of fumes and smoke, even when idling. I briefly mentioned it to my mechanic and he said I should get a performance exhaust to increase the backpressure on the engine. (I havent had him thoroughly inspect the problem). What's you input?

If the smoke is blue it is burning oil. If it blows more blue smoke when accelerating it is either a stopped up crankcase vent system or bad rings or over filled with oil. Also you need to check to see that the oil is not diluted with gasoline.