First, I tried retarding the ignition about 5 degrees and then did a test drive. The buzzing noise still kicked in at the same point as before. (With retarded timing, you would expect pinging to be reduced/delayed as you accelerate.) Second, I notice that the buzzing gets considerably louder and clearer whenever I turn on the heater.
My supposition at this point is that something in the exhaust system - either the heat exchanger or exhaust component(s) near the heat exchanger are rattling/buzzing. The buzzing doesn't start until things heat up, BTW. I'll do some further poking around to see if I can find anything visibly loose in the exhaust system.
I'm wonder how to deal with this if it turns out that the noise is coming from *inside* the heat exchanger. Any ideas, anyone?
On another note, I think I fixed that pesky oil leak that was driving me nuts. It turns out that the three small bolts on the front of the camshaft housing - including the one that extends down through the cylinder head and into the cylinder barrel assembly (the one that the ground strap ties to) - weren't tight. (They were probably only tightened to 1 or 2 foot-pounds max!) Now that I've tightened them up, it appears that the oil leak has stopped. The most obvious manifestation of the problem was that oil had been getting all over the fan assembly, including the fan belt and pulleys, so I had assumed that the oil was seeping out at least as much from the rear of the head area. But apparently it was merely a case of oil leaking from the front area of the engine and then seeping back along the cooling fins and then getting blown onto the fan.
Richard
--- In
2cylinderhondas@yahoogroups.com
, "richmccolman" wrote:
> Thanks, Don, Miles, et al.
> So far, the noise doesn't appear to be associated with the engine side shrouds - when I press on the shrouds with a big screwdriver as a rev up to get the noise, the noise doesn't dampen out. Currently, the leading candidates for the noise are rattle in the heat exchanger and engine pinging...
> Yep - I have a strong suspicion that the 178 psi compression pressure listed for the z600 in the coupe manual is incorrect. Interestingly, I checked out this online compression pressure calculator site...:
http://www.not2fast.com/turbo/compressi ... sure.shtml
> ... and when I plug in the parameters:
> - 8.5:1 compression ratio
> - 1 for stroke and 1.5 for rod length (as recommended on the site, for most stock engines)
> - 270 for cam duration (as recommended on the site for standard cams and solid lifters)
> - 0 meters altitude
> - 70 degrees F temp
> ... I end up with 167 psi - very close to what Miles said. (Knocking the CR down to 8.3:1 as listed in the sedan manual gives a figure of 162 psi - again, within the range Miles indicated). (I also double-checked this online calculator by plugging in numbers for an air-cooled Beetle with 7.5:1 compression ratio - with which I'm already familiar- and the resulting 141 psi compression pressure figure is exactly what it should be.)
> So it does indeed appear that my the compression pressure readings of around 180 psi on my coupe are high after all. (BTW, temporarily I swapped out the compression gauge with the air regulator gauge on my air compressor and found that it reads within 2 psi of the compressor's gauge - essentially it's accurate, I assume.)
> Is the 180 psi compression pressure high enough to cause pinging? Not sure. As an experiment, I'm going to try retarding my ignition timing by a few degrees to see if that reduces or delays the higher-RPM noise I'm getting. If it does reduce the noise, I'm guessing that will confirm that what I've been hearing is pinging (caused by carbon buildup). If retarding the timing has no effect, then I'll assume the noise is due to another cause.
> Okay - I've rambled on with all this far too long.
> Thanks again,
> Richard
> --- In
2cylinderhondas@yahoogroups.com
, Don B Laughton wrote:
> > Up until the Z600, and more so with the Civic, the shop manuals were pretty much "universal". Some it might cover a range, like the 360/400/600 shop manual...that's why it has the Hondamatic section. Anyway, there is only one 600 piston design, but there are two cylinder heads. One is for the 45hp N600 engine the other is for the 36hp N & Z600. The drop in compression ratio was probably part of the de-tuning of the engine. If you think this is bad, one of my jobs at American H was to check all the metric to English conversions is the manuals and to proof read them to make sure they made sense in English. There is a Z600 Owner's Manual with a odd introduction. I rewrote it, had it typed, red lined the section to be deleted and sent it off to Japan. The manuals came back with both sentences! There pistion spec given in the four cylinder S600 shop manual is for the 49mm T360 piston, not the the 54.4mm sports car engine. Hope this
> > offeres some insight to how things were in the early days. Best Wishes, Don Laughton
> > From: richmccolman
> > To:
2cylinderhondas@yahoogroups.com
> > Sent: Saturday, September 22, 2012 3:34 AM
> > Subject: [2cylinderhondas] Re: pinging... maybe, high compression, decarbonizing
> > Thanks for the input, Miles.
> > I'm still curious about the spec in the coupe manual. At first, I thought my compression reading of 180 psi was too high, upon seeing the 156 psi spec for the n600 in the sedan manual, and mistakenly finding the 149 psi spec for the z360 and - I figured at that point that the 180 psi reading was indicative of carbon buildup in the combustion cambers. But since the z600 spec listed in the manual says 178 psi, I figured the 180 psi compression reading I was getting was okay after all.
> > Is there reason to think that the 178 compression pressure spec in the coupe manual could be a misprint? If so, perhaps I do indeed have a carbon buildup issue. (BTW, when I got the car, I was told that the previous owner had recently rebuilt the engine.)
> > Interestingly, I determined that the comparatively lower reading of 164 psi that I originally got on #2 cylinder was due to worn spark plug threads not allowing the compression tester to seal completely. A subsequent test I did after I managed to wrangle a better seal gave me a reading around 180 psi on #2 - similar to #1 cylinder. (BTW, I repaired the spark plug hole on #2 yesterday, and will try running the car today once the sealant for the thread repair insert fully cures. I started to wonder after doing the repair whether the "buzz" noise at higher RPMs could have been due to leakage past the spark plug on #2. I'm really suspecting that it's something else causing the noise, but I'll find out shortly.)
> > Thanks again,
> > Richard
> > --- In mailto:2cylinderhondas%40yahoogroups.com, "feltonminicycle" wrote:
> > > Standard compression on a fresh rebuild is about 160 to 165psi. Normal pressure after full break in and possibly years of driving typically is 150. 110 is about the least it will run on.
> > > On the high RPM buzz, just stand in front of the car with hood open running and slowly manually raise the RPMs and listen for the buzz. Could be fan bolts, missing fin dampers, side shrouds, special hardware on the heat exchanger to clutch cover and dislodges fins inside the heater box.
> > > Miles
> > > --- In mailto:2cylinderhondas%40yahoogroups.com, "richmccolman" wrote:
> > > > BTW, as I was checking the compression specs, I noticed something that surprised me. The 600 coupe engine is rated as having an 8.5:1 compression ratio (with a normal 178 psi compression pressure). However, the engine specs in the sedan manual say that the sedan engine has a 8.3:1 compression ratio (with a normal 156 psi compression pressure).
> > > > I had previously been under the impression that the only major difference between the coupe and sedan engines were the camshaft, camshaft housing, left camshaft housing cover, and valve cover - to accommodate the tachometer linkage. Apparently I was wrong about those being the only significant differences.
> > > > Just out of curiosity, what other fundamental differences exist between the sedan and coupe engines? At the very least, the differences in the above-listed specs would seem to indicate that the geometry in the combustion chambers are somewhat different between the two.
> > > > Richard
> > > > --- In mailto:2cylinderhondas%40yahoogroups.com, "richmccolman" wrote:
> > > > > Tad and Eric -
> > > > > Thanks a bunch for the ideas. I'll check those things out.
> > > > > Richard
> > > > > --- In mailto:2cylinderhondas%40yahoogroups.com, Eric Geiger wrote:
> > > > > > thats a very good list of ideas. i would also add in to make sure all the rubber between the fins on the head and block are there it could be a weird vibration if you are missing the rubber spacers between the fins
> > > > > > Eric J. Geiger
> > > > > > PRG Nocturne
> > > > > > XXX-XXX-XXXX phone
> > > > > > XXX-XXX-XXXX fax
> > > > > > XXX-XXX-XXXX mobile
> > > > > > egeiger@
> > > > > > www.prgnocturne.com > > > > > On Sep 20, 2012, at 8:26 PM, Tad Clark wrote:
> > > > > > Check the gromets on your cylinder cooling shrouds. If they are worn through they will buzz at upper revs. Also, make sure your exhaust isn't rubbing on the underside of your car. Deteriorated motor mounts are likely a reason for this.
> > > > > > From: richmccolman >
> > > > > > To: mailto:2cylinderhondas%40yahoogroups.com
> > > > > > Sent: Thursday, September 20, 2012 6:10 PM
> > > > > > Subject: [2cylinderhondas] Re: pinging... maybe, high compression, decarbonizing
> > > > > > Ahh... it turns out that I was looking at the z360 compression pressure number (149 psi) in the manual. The z600 compression number in the manual is 178 psi. So it looks like I don't have a carbon buildup problem after all! Whew!
> > > > > > Now I still need figure out what's causing that nagging buzz around 4,000 rpm. But at least I know it's not pinging caused by excessive compression pressure.
> > > > > > Richard
> > > > > > --- In mailto:2cylinderhondas%40yahoogroups.com, "richmccolman" wrote:
> > > > > > > When I first got my coupe, I discovered that ignition timing was set waaayy too advanced - something like 40 BTDC! I'm amazed (a) that it ran at all, and (b) that the engine hadn't self-destructed. Needless to say, I reset the timing to the F-mark, and it runs smoothly - except that...
> > > > > > > I've been having an issue in which I get a significant noise - best described as a "buzzing" - that kicks in around 4,000-4,500 rpm. My worry is that it's engine pinging (though it's hard for me to isolate the source - I hear it in the cabin, but have yet to hear it above the general engine noise standing at the engine and revving it at the carb). However, the engine compression test does read high. #1 cylinder reads about 180 psi, and #2 reads about 164. (Specs in the manual say it's supposed to be 149, or 154, depending upon where in the manual you look.) After checking the compression just now - similar numbers to above - and seeing it was reading high a few months ago too, I took a stab at back then of trying to decarbonize the engine using water mist into the vacuum line for the power brake booster (revving the engine while doing so, of course).
> > > > > > > It still buzzes around 4,000 rpm, but I'm not convinced that what I'm hearing is pinging -again, I hear the buzzing in cabin, but can't really detect pinging listening directly to the revved engine, above the general engine sound. As I drive it, the car makes a host of rattling, etcetera, noises from the dashboard area (par for the course with these 40 year old cars, I suspect, so I'm not sure whether the 4,000 rpm buzz is engine-related, or just stuff buzzing inside the car. I also wonder if there's some kind of vibration in the exhaust system that doesn't kick in until about 4K.
> > > > > > > What I do know is that the compression readings are high - assuming that my compression tester is reasonably accurate.
> > > > > > > Any ideas?
> > > > > > > Also. has anyone tried a decarbonizing procedure that's worked well, and if so, what did you do, specifically?
> > > > > > > Thanks,
> > > > > > > Richard