|08-08-2010 03:53 PM|
I took the distributor apart down to its main components. Bushings are good, springs were swapped from a known low-km distributor. I cleaned everything up and lightly applied some grease. Shaft end play does have some slop to it, and looking online this is fairly common in these stock units. A
lthough not desirable I doubt its the cause for my concern, especially after what I learned during the compression test. More on that in a minute.
I re checked my initial and total timing, and found that the mechanical advance adds 20* by 3500ish rpm.
Compression test yielded results of 140-145 psi across the board EXCEPT for cylinder number 2. This guy was at a pathetic 95 psi. I poured a bit of oil in the cylinder and retested, now at 90 psi. Something tells me it's not the rings.
Since compression was good on the adjacent cylinder, it leads me to believe it's not a bad head gasket.
Next logical step is to re-adjust the valves using the method you linked. I'm crossing my fingers it's not a bad valve.
I checked the spark plugs and attached the image.
Cylinder one has some porcelain cracked off of it, probably from detonation while I was messing with the timing.
Cylinder two looks like all the rest, if only slightly less tan-coloured.
Cylinder three has some really weird deposits on it, although compression was good on this cylinder so I don't understand.
Cylinder seven has some pretty hefty oil deposits on one side. I'm not surprised at all that these valve seals leak oil.
|08-07-2010 04:18 PM|
|08-07-2010 10:38 AM|
I've got a few distributors kicking around actually. I'll swap this one out for another, and see if my readings change. It's entirely possible it's worn out, the 305 it came from had 250,000km. But it ran good, which is weird.
I bought a compression tester. I'll give that a try today. I don't have a leakdown tester, but I did have the heads looked at by the machine shop. They said all valves but one sealed fine. The one had a slow leak. They recommended a complete valve job, but I couldn't drop an extra $1000 on it.
I didn't degree the cam. I did verify the TDC mark with a dial gauge though.
Should I look into re-adjusting the valves?
|08-07-2010 09:42 AM|
I mentioned that before you get into the tuning you need to ensure that all aspects of the assembly are tip/top that would include the valve train. Have you done a compression/leak down test lately? how many k on this motor? did you degree the cam when you put it in? did you ensure the balancer pointer is in fact at TDC? timing chain type is of little concern here as long as it is in good shape and installed right, vacuum reading interpt,,, look at this http://www.classictruckshop.com/club...ts/vac/uum.htm
you can use the vacuum gage to help narrow down issues, there are other sites with annimation, hope this helps,,,keep on it,,,the carb is going to be next.
|08-06-2010 07:34 PM|
News news news! Apparently I've been mistaken. I had my vacuum advance hooked up the way it was from stock with the 305.
Initial timing with vac advance disconnected, at idle, out of gear is 12*
Connected, it's 30*, at idle, out of gear.
It must be a manifold source at the carb, since it's advancing 18* at idle with vacuum advance connected.
That said, I ran the tests you asked me to, to figure out total timing.
Vacuum advance disconnected, I revved it to 3500, at which point it stopped advancing, staying at 30*.
Vacuum advance connected now, I revved it to 3500 again, and it stopped advancing at 50*.
I checked the manifold vacuum at idle again, and noted that indeed, it was around 14-15* at an idle roughly 750-800. Again, it idles very rough.
|08-05-2010 09:27 PM|
I hooked the vac advance canister to manifold vacuum and gave that a try. It does idle quicker, but it's still not any smoother. I'm beginning to wonder if my problem lies elsewhere, so I'll provide all the details I know.
The heads are flat washer plug heads with 76cc chambers from a 69 chevelle. I'm running R43S plugs, and I checked them today and didn't notice any real discoloration. Maybe a little light, if anything. But they're brand new. 300km on this thing.
It's been a while since I ran a car without a catalytic converter, but is it supposed to smell like a lawn mower?
I read in the manual that came with my cam, not to use late-model timing chain sets. I just ran a basic double roller for a small block Chevy. I don't know if this matters, but I'm mentioning it.
I read online that a low vacuum at idle could indicate either a slight intake manifold leak, or retarded valve timing. Should I start looking in these areas for a solution to my rough idle?
Maybe my valves aren't adjusted right. I tightened them down to zero lash, then 3/4 of a turn past that.
Bad valves maybe? I would have thought that'd be indicated on the vacuum gauge.
|08-04-2010 11:22 PM|
Sorry, I forgot to mention I didn't get a chance to mess with the new timing light yet.
I think I set it to 600-650 in gear. I'll re test it as soon as I can with the RPMs noted.
Leave it to me to mess with a good thing. This car had a great running 305 with 250000k on it. What a headache this new engine is turning out to be! Once I've got it tuned, there's still the matter of a heavily leaking rear seal to contend with!
I really appreciate the help so far!
|08-04-2010 08:39 PM|
|Custom10||did you switch to manifold vac for the vacuum can on the HEI? did you see what your total advance (initial + mech) was with the vac can disconnected when you reved it to 3500? is 3500 enough to get the mech advance to stop moving or adding advance? did you check what the total advance is with the vac can hooked up (initial + mech + vac advance) @ 3500 rpm?, 15 "hg is not bad, what was the idle rpm at this value? I would expect more than 15 " hg at 800 rpm in park with a 204/214 duration cam, not a big deal with only 15 though.|
|08-04-2010 08:04 PM|
I just picked up a timing light with a dial. I needed one anyways, let's see if they let me return the old one!
I also bought a new vacuum gauge. I've seen the old one around here hundreds of times, but it's hiding on me now and a new one was only 15 bucks.
I stuck the vac gauge on there at idle, out of gear. I fired it up, and at first it fluctuated from 14-15 in-hg, but soon leveled off at 15 in-hg with a little needle shake.
|08-04-2010 06:08 PM|
INHO, forget the initial timing. Get a dial back timing light or a timing tape. SBC, unless it is a newer vortec engine, like 34-36* total timing @ <2800-3000 rpm. Total timing is centrifugal + initial without vacuum advance hooked up.
If you set the timing this way, forget about what the initial timing is. Just make sure you do not exceed 34-36* at higher rpm. This number is for maximum timing regardless of maximum rpm. It may take a distributor kit to accomplish this. Also, this is a base setting. For maximum performance you will have to dial it in as each engine is different.
Vacuum advance is a whole different ball game. Either use a Crane? adjustable vacuum advance kit
or a correct GM vacuum advance unit based upon your idle vacuum and limited to 14*. This will give you 50*. Use manifold vacuum not ported.
|08-04-2010 10:20 AM|
|Custom10||Most performance cams will benefit from more initial timing at idle your setting of 12 with this cam is OK for now, the higher the duration the more this applies and on top of the base timing the vacuum advance will add another 20+ or so at idle with a stock HEI, IF you put a timing light on it at idle with the vacuum advance connected to manifold vacuum you would have seen this, it would be around 34-36 BTDC at idle. I was trying to determine if your vacuum advance was adding anything at idle. Since you are on ported vacuum there will be very little or no added advance at idle due to vacuum cause the ported side is above the cab throttle plates which only see's engine vacuum when you increase the throttle opening. So as far as the ruff idle goes if you switch to manifold vacuum you will most likely take care of this issue cause you will be adding in another 20 degree's give or take, give this a try, when you switch to manifold vac your idle rpm will increase once connected to the vac can, then disconnect it and insure that the timing drops back to 12, this will verify that the vacuum advance can is working. Set your idle to about 800 rpm with the vacuum advance connected, drop it in gear and see if your idle quality improves, it should drop to about 650 rpm or so and smooth out. Next is to determine the mechanical advance curve added by the HEI dist. You can do this first if you want. Disconnect the vacuum advance plug the hose, use the light to check the initial timing at idle it should be back to 12 right, then rev the motor up while watching the timing light you should see the timing advance increase, keep giving it throttle till the timing stops advancing and note the RPM at which this happens, most likely about 3500 rpm and also note what the timing is, you want about 34-36 degree's BTDC. Some balancers will not afford this as they only show 20 degree's BTDC, if this is the case then you need to make a timing tape or get an light with a turn back pot. Some HEI dist will add more than the numbers I listed but give this a try to see what you have got, it may be necessary to limit both the mech and vacuum advance ,,,we'll see,,, if you run 18-20 initial as I do this limiting is a must but your cam does not need that much initial.|
|08-03-2010 11:07 PM|
I'll have to dig around for the vacuum gauge in the garage. I saw it somewhere before...
Everything else you mentioned doesn't seem like a likely culprit. It all came off of the 305 that was in there, and it was running and idling great. Cap and rotor are new, wires are new, plugs new, fuel filter is new, fuel pump is new and the carb has ran great on two different motors.
The vacuum advance is connected to a ported source on the carb. When I set the initial timing, it was with the vacuum advance disconnected, line plugged, in gear and at 500 RPM.
Did you want me to check the difference in initial timing at idle, with the vac advance connected, then disconnected?
I'll definitely get back to you with the manifold vacuum readings at idle.
|08-03-2010 12:15 PM|
Basically at this point you are trying to figure out why the ruff idle by eliminating possible causes, once everything checks out OK then you can proceed to tune it.
Don't worry about hurting your convertor with a little more idle speed in gear
|08-03-2010 07:22 AM|
|stfinney||Every setup and engine is different and likes a different setting. Try setting your total advance at around 32-34 degrees and see how it runs. A little more idle is fine, not much at all. What stall converter do you have? Mine was a stock version and did fine.|
|08-02-2010 10:19 PM|
I'll try running a bit more initial advance. It seemed to like it, but I settled with less advance thinking it was on the safer side.
|This thread has more than 15 replies. Click here to review the whole thread.|