Greetings, I'm re-posting this in the technical section. I probably violated some etiquette, but I'm hoping it will get more exposure here. I'm still trying to get my TR engine out service complete (first it's had since an engine replacement 25 yrs ago), but I'm struggling with timing the cams. I did my 308 with no problems. Everything made sense and the numbers came out spot on as expected. Not the TR though. The 1-6 intake cam is now perfect, but the 1-6 exhaust doesn't seem right. From what I understand it should open 54 deg. BBDC and close 10 deg. ATDC. If this is wrong then this is the problem and I would appreciate knowing the correct values ('86 US version). If not, I'm finding the exhaust opens at 51 deg. BBDC and closes at 8 deg. ATDC. I would have expected 12 or 13 deg. ATDC for it to close if 51 deg. was truly indicating the cam was lagging by 3 deg. I zeroed TDC using both cylinders 1 and 12 to make sure (hard stop and dial). I adjusted the 0.5mm clearance up and down slightly to see the effect and saw very little (I also did it with normal valve clearance and measured at 0.5mm lift). I then switched to the other lobe on cylinder 1 and found the same numbers within a line width. This is a low mileage car so I don't think it's lobe wear. The interesting thing is that the pre-cat on this bank is half burned out - exhaust timing off? Is it better to bias the timing or split the difference? Any help or thoughts would be most appreciated. It was suggested in the TR forums to try different cylinders which I'll do this weekend. Thanks.
I read your post twice now and I am not sure what the problem is. 1. Do you not have the right specification for the exhaust cam? It should be in the manual. Follow that and you will be home free. If the exhaust cam does not meet your specs in the WSM, re-do it until it is right. 2. I find that using the center-line method is easiest for me to understand and explain to people. It also avoids having to compensate for the initial 0.5mm gap. By the way, the TR section has some of our most illustrious members like Steve M. He would be the one I listen to.
The short explanation is that he's measuring less duration (at the 0.5mm clearance) for both #1 cyl exhaust lobes than what the OM/WSM "spec" indicates -- so he wouldn't be able to hit all three targets (open, mid, close) simultaneously. I have no better advice than what others have already given -- get more information: 1. Measure the duration on exhaust lobes for other cylinders of the 1-6 exhaust cam -- if they are all the same = mismanufactured or measurement technique error?; if they are somewhat different (i.e., some match spec and some don't) = wear? 2. Measure the exhaust lobe duration on multiple cylinders of the 7-12 exhaust cam for additional comparison -- if you get the same undersized duration on all = something wrong in the measurement technique? (as you have a better chance of winning Lotto than getting two mismanufactured cams ); if you get the correct duration on all (but all lobes on the 1-6 ex. cam are under-duration) = confirms the 1-6 exhaust cam is slightly mismanufactured? If it truly is an under-duration condition, I think that you could make it work OK. If it was an over-duration condition, that would be a tougher decision for how to set.
Mr. Magnusson, You are correct in understanding the problem. I will check all cylinders this weekend. Interestingly, the intake cam on 1-6 was perfect. I don't see anything different that I'm doing on the exhaust, but as you mention, I need to get more information. I checked both valves on #1 exhaust (same result) and changed indicators and fixtures to make sure I wasn't missing something, but nothing changed the results. I have numbers for the 7-12 intake and exhaust which are normal and just need adjusting. I'll update this weekend with what I find and maybe it will determine the path to take. Thank you for your input.
That's certainly a good thing, and exonerates your measurement technique (which I don't mean to impune unnecessarily, but I only have the information that you post). I'd have to say that getting the exact same out-of-spec result on the two cyl #1 ex. lobes seems a little too coincidental for wear, but a measurement of the other 1-6 ex. cam lobes should let you separate whether it's a wear issue or just a manufacturing error. One other thing you might do is measure the maximum lift of the 1-6 ex. lobes vs the 7-12 ex. lobes. The contact pressure between the lobe and the shim is much lower in the open and close regions of the lobe (vs the peak) so if those areas are worn enough to detect/measure, I'd guess that the peak of the lobe would be severely worn -- just a thought (i.e., if the lift is still the same then that's another clue that it must just be a manufacturing error and not wear)...
Mr. Magnusson, I hadn't thought of checking the overall lift and comparing it to the 7-12 bank, though after you mention it, it seems obvious. I'll get the lift for the lobes as well. With enough data points filled in, the problem should show itself. It could be something I'm doing wrong, just tell me what it is, I won't be offended. If I have time tonight, I'll try to get some numbers. Thank you again for the input.
Mr. Magnusson, I have to conclude it was me, sort of. I went back and remeasured everything, but before I give away the answer... The lift was consistently .002" less on the 1-6 ex. cam than the 7-12 ex. cam. The lobes are near perfectly ground between the two valves on all cylinders. The timing from one cylinder to the next is within a fraction of a degree. This leads me to believe these are actually well made cams. The problem was with the dial indicator and how I had it placed. I wasn't getting repeatable results and realized that a combination of stiction and insufficient indicator preload caused the odd timing readings. I switched to my shop indicator and the readings made sense. The cams are now timed within one degree of the spec. and I'm good to go. Thank you for being a sounding board and making me question what I was doing, because in the end it was me. Brent
Very good to hear. The dial indicator has gotten me many times too. The thing is we amateurs don't do this day in day out in order to develop good skills, acquite repeatable set ups ready to go any time. Every time I touch this, once very 6 months or so, I have to read up on it all over again.
