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Triumph TR6 - Timing Survey
Last weekend I installed an Allison (I think its an older Crane system) Electronic ignition unit in my '71. Its at this phase of the restoration I figured on checking/setting the timing. Also added new wires and cap. Car runs reasonably well, but due to fairly frequent low speed backfire, I'm assuming I still have a timing problem even though I set it per the manual (strobe).
I checked this website's archive for timing info. Found that people are using settings way off the Haynes and Bentley manuals' recommendation. The books call for static of 10 deg.BTDC and strobe at 4 deg ATDC. The archive of this BBS had guys telling of advancing into the 20+ BTDC range
I indeed noticed the more I advanced it, the smoother it sounded, but thought I'd survey you guys to see what settings you're using and how satisfied you were.
|Mark--Are you certain your carbs aren't running too lean? Suggest you read your plugs first to confirm correct mixture, then advance the timing beyond 10 BTDC in small increments and road test for telltale detonation (pinging). |
I think it is the timing - as you say low speed popping is the tell tale sign (is it hesitating on low speed acceleration too?) - I had a similar problem when I went to triple weber conversion and it was cured by increasing the advance. I am running a lot of advance -probably close to 20 degrees at idle. I think you have to start twisting that distributor a little at a time to see what sounds good and what feels good -you will be able to tell when you drive it - it should pull smoothly without hesitation.
hope that helps!
|The reason for a wide range of timings will be related not only to mixture but also to compression ratio. UK cars has 9.5 CR while USA ecports went as low as 7.75. The lower the CR the slower the fuel mixture burns and the more advance is needed. So as the posts above say, set it up until the engine speed is optimal at tick-over and ignore the books.|
Just as a reminder, if you install electronic ignition you should change the gap setting on your spark plugs from the standard setting of .025" to .040"/.045". This works best on my engine. I also use Champion RN 12 YC because they have solid ends (where the wires attach to). The screw on ends no matter how tight you make them get loose enough to create ignition problems. Best of luck, John P.
|I was actually playing with adjusting my timing today, and since I am new to TR6's, I thought I was reading the books wrong. I.e. I tried to set timing to 4 ATDC, and the engine coughed and sputtered, so I tried 4 BTDC, and things seemed much happier.|
So I guess I am going in the right direction, I will advance the timing a little more, but is 20 ATDC common? I will try to read up on the archives, but this seems pretty far up there for 850 rpm.
|Ignatius--Actually, your timing should be advanced between 10 and 20 degrees BTDC, not ATDC. Also, as the posts above indicate, toss the books and go by seat of the pants performance. Just make sure you're not into a preignition condition (pinging) and your carbs are tuned. Rick O.|
|Phew, I'm glad I read this thread. I thought I was going crazy, too. I set my timing according to the books and the car ran like crap. It smoothed out only after advancing the timing to around 16-18 degrees BTDC. I'm glad I'm not the only one who couldn't figure this out!|
|Chris--Was that 16-18 degrees BTDC set with a strobe at idle (850 - 900 rpm)? With or without vacuum retard connected? Thanks. Rick O.|
|Rick, that was set with a strobe at 850rpm idle with the vacuum retard disconnected.|
|I've had the same problems with setting the timing on my 74. I ended up at 16. Since then though, I've rebuilt the engine, carbs, taken off the factory A/C and made a few other changes. I will email back in a week to let you know were I end up with my timming.|
I do have a question though. Can setting the timming too advance cause the engine to overheat? I've also heard that having the carbs too lean will cause overheating.
|Hey Y'all (This probably does not come across on the BBS, but this is a failed attempt at a southern drawl.),|
On my 74, I am now at 12 BTDC with a strobe, but my idle speed fluctuates slowly between 500 and 1500 rpm, and I can not seem to keep it settle it to 850 rpm. I.e. my slow idle screws are pretty much out, and no, my fast idle screws are not touching the choke thingey. Is this a sign of another problem?
I have all the vacuum/emissions BS hooked up, and just replaced one of the elbows since it had a leak. And the vacuum retard is hooked up to the distributor. I checked the temperature compensator on the front ZS carb and that seemed fine. I will check the other one tomorrow, but is there an easy way to check the bypass valves with out taking them out? I can not remember which book I was looking at, but it sounded like these valves may be the problem, and the only option it gave, was to replace the pieces. These are pretty pricey at Moss.
|Ignatious--Sounds like your air bypass valves are indeed floating or close to it. Very easy to adjust IF yours are open on the end (mine weren't, so I had the brass caps removed). I believe clockwise is float, CCW is to seat. You want to turn just to valve float, then CCW one turn. Also, I incorrectly installed the gaskets on my bypass valves which took me a long time to figure out. Worth checking if unsure.|
|Mark H, et al:|
There is an excellent article on timing at WWW.mit.edu/people/zimerman/Documents/tr6/advretard. This is John(?) Zimerman's web site at MIT. It is currently down, but I'm sure it will be back soon.
Depending on which distributor you have, it talks about how the advance and retard functions work. At idle, if retard is working, vacuum would subtract 16 deg of advance from timing. Therefore 12 deg BTDC at idle (without vacuum retard attached) equals 4 deg ATDC on the stobe (with vacuum retard on).
I would detach vacuum retard (and Advance), plug lines, and start with 12 deg BTDC and increase from there as much and engine will stand without pinging under load. This will require trial and error testing by accelerating in fourth gear going up a hill.
I had problems with timing on my 74 TR 6. I had to advance timing to 28 deg BTDC, before my car would run well. The problem turned out to be the distributor itself. I think the upper bushing in the distributor was worn causing the dwell to jump all over the place.
If Zimerman's site doesn't come up soon, email me off list, and I will send you a copy of the article.
|The last time I checked out Zimer's site it said he was no longer a student or employed at MIT, so therefore his site had been shut down. If that is the case, hopefully he will bring it back online somewhere else.(plot for bad "B" movie)|
|I think I have my TR close to being tuned, but I need to tweak things a little more.|
As Rick O. suggested, I adjusted my bypass valves so they were floating less. Tweaking this narrowed the range on my timing between having the distributor retard on and taking it off ranged from 4 ATDC to ~12 BTDC, which seems inline with John K's note. Without retard, I was up to about 16-20 BTDC.
So my questions are:
1.) When I was adjusting the bypass valves, I started with the front carb, and set it so that rev was about 1300 rpms without distributor retard connected (~850 otherwise), but I did not seem to get much response out of the rear carb. Is this normal? Now that I think about it, I do not remember there being a vacuum attachment between this carb and the distributor. Is there another way to set valve float on the rear carb?
2.) While running, I hear a slight Tinking noise in the rocker head. Kind of like "pinking," but not quite as obnoxious or distressing. I checked the clearances for the valves and that seemed OK. Any thoughts?
3.) I am inclined to try advancing my timing more. On advancing the timing, I think I read something (I can not remember where now) about doing this with the engine OFF. On other cars I have done this while running. What is the proper thing to do for a TR?
I agree with John about the retard. I think you are on track. You should read the bentley manual though. I would start with the Bentley manual leaving the retard connected and then slowly increase the timing. You will have to drive with each change. When the timing is set with the engine off that is static timing. I just rebuilt my 74 TR6 engine and set the timing by the book at 4*ATDC with the retard connected. Which is exactly what the Bentley manual states. This is with new timing gears, chain, a working distributor retard, and plug gap of 35. However, I do have a 73 cam and the EGR connected. Prior to my rebuild I set the timing at 16*BTDC with retard disconnected. I've had allot of advise on setting the timing and seemed to always have something a little different. I think you cannot go wrong when you go with the Bentley manual. However, there are other factors. Like worn timing gears, distributor, etc. Before my rebuilt my carb needles were worn and running too lean. This along with a worn engine and worn timing gears and chain caused me to try many different timing settings. If your distributor is not jumping timing and your engine is not completely worn out. I would simply replace the timing gears and chain, and rebuild the carbs. By the way I have the Ignitor by Petronics which I think is great. A couple of nice items are the carb sync from J.C. Whitney, and a colortune. After setting the timing as close as you think is correct for your engine (ie, worn gears, etc) check the sync of the carbs then check the color of flame in the combustion chamber with the colortune. Before my rebuild, my carbs were too lean and the combustion yellow which caused the exhaust to be too hot causing the exhaust manifold to crack. I found this out after the exhaust manifold cracked. I do not know much of the bypass valves, and I'm curious to know your outcome of your rpm fluctuation. I think I'm close to the same situation as you with the rpms. I'm not a pro but have tried others advice (and appreciate it all) and have come to the conclusion; everybodys car is a little different but I still ask for all the advice I can get and then try what I feel is best.
|Ignatious--Try strobe timing at TDC (zero degrees) with retard at idle and advance from there in small (2 degree) increments. I don't know why static timing (with the engine off) would offer any advantages over dynamic. On my 72, the bottom of the rear carb has the vac connection for the thermovalve/retard capsule. When was the last time you rebuilt the rear carb's air valve? It could be stuck or improperly assembled (mine were) thus not giving the rise in idle you're looking for. Don't know about the pinking--does it respond to changes in timing?|
And I thought it was going to be easy to set up the timing and carbs this spring. Rick O, I had my carbs rebuilt and obviously he did not adjust the Bypass valve. Also mine are (where) like yours...non external adjustable. Could u be so kind please and go into a little more detail as how u converted them to external adjustable? I did not think these kritters where that important as to carb adjustment. A MOSS catalogue says "do not alter setting" is this a case of "do not beleive everything u read"? I also have "popping" noise (deceleration only) and read with interest the thread " backfires". At end of season I noticed my retard connection had come off the back carb and is now "clamped" on.
|Bear with me on this first question. When dynamically adjusting the timing do you leave the engine running? Something I read said to get a timing reading, then turn the engine off, turn the distributor, and check again with the engine on. This later method sounds like a pain in the boot, nor does it sound very "dynamic". What is the proper method?|
Rick O, I just looked at the Moss diagrams for the vacuum, and it looks like the 72 did have vacuum connections for both carbs, but starting in 74, they only go to the front carb. Hopefully this is why I do not get any response from the rear carb when I play with the float adjustment. The pinking/tapping seems to go away with more advance, but that seems the opposite of normal pinking situations. I will start a new thread on this question.
Casey, I think my engine is good, i.e. oil pressure and compression seem fine (knock on wood). Is there an easy way to check the wear on the timing gears and chain? Also, is the 35 gap on your plugs an adjustment to having the modified ignition, or the cam? I have my gap set to 25. I really like this colortune idea. I take that you recommend this highly?
|Rick C. If you have the brass cap on the end of the air valve cover, remove the valve cover and secure it upside down in a vise. Using a similar diameter punch or valve stem, simply knock (or drill out) the brass cap out of the valve cover (it was a compression fit at the factory). Reassemble and you'll have access to the adjustment screw slot without removing anything! Bentley tells how to do the float procedure. Good luck!|
Timing chains are not hard to replace on the TR6. My opinion is this is a much overlooked area from all auto owners. Newer cars usually have timing belts that are suggested to be changed every 75,000 miles. When they break, especially on a 300 ZX the valves usually bend. Older cars and heavy autos have timing chains that usually just wear a little and stretch. Some of the finest and most reliable that gave many years of service before changing were the Mercedes 450SL that used double timimg chains.
If you decide to check, I beleive the radiator, and cross member will have to come out. To check for wear; well you will probably have to compare to a new gear. AS far as stretch of the chain, you can not.
The wider plug gap is for the Ignitor. The colortune is easy to use. You will never have a too lean mixture but you might end up with a little to rich. The instructions are pretty simple.
By the way, alot of 6 owners in this area are closing off the bypass valve by making a gasket that is the size of the cover. I have not tried this, but I think I might. Also VTR has an article on the TC. About putting it in hot water to ensure both open at the same time. I've heard alot of 6 owners just screwing the nut tight.
This thread was discussed between 22/03/2002 and 10/04/2002
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