Kentetsu

Well, that's what I'd call it if this was a boinger motor.... Here's the situation:

Drove to Lansing for an Autocross, about a 90 mile drive which is no big deal for my racer/daily driver. But when I get off the freeway and into town, I heard a strange noise coming from the engine. You know how an old V8 with a rod knock will sound when you get on it? Well, that's about what it sounds like. Clack, clack, clack, clack, etc.

Now, it gets even stranger... This only happens when the secondaries open. I've got mechanical secondaries, so I control when they open. I can take it all the way to the redline on primaries only, and everything sounds fine. But as soon as I open the secondaries (at any rpm), then she starts with the clack, clack again. This happens whether driving or revving while parked.

Had a couple of guys at the race listen to it, and they all agree that this is a real head scratcher. We couldn't even really tell where the sound is coming from. A couple of ideas were a possible exhaust leak near the RB header, or that the sound was coming from the intake or carb.

I pulled the cover off of the carb and checked it out, but couldn't verify where the sound is coming from. Fuel flow looked excellent, both primary and secondary getting a great clean shot.

The engine may be idling a little more roughly than usual, but its hard to tell. She has always idled like I had a small vacuum leak anyway, just a little rough. Power output remains unchanged. I even ran both events that day, and there was no change in the condition of the engine or the noise it was making. Made the drive home okay too.

Oil and coolant levels are fine, as are oil pressure and temperature. I tried increasing the fuel pressure, even to the point of smoke from being over-rich, and it changed nothing. Retarded the timing slightly, and again no change.

What in the world could be happening to make this sound only when the secondaries open? I'm truly stumped on this one. The engine has 212,000 miles on it, but has always run fine for me. Maybe its just time to retire that one and source another? If so, then that's fine. But I still want to know whats happening here...

ray green

iTrader: (14)

Here's two wild guesses:

1. timing is off.

2. an apex seal or two is not completely sealing, so that under the high fuel dose from the secondaries fuel slips by into the exhaust stroke, where it detonates.

3. it might be time to fix that vacuum leak, just in case.

Ray

Kentetsu

Thanks Ray. I already tried retarding the timing, with no results.

Rotaryhaven

iTrader: (17)

Slightly spun bearing???

blwfly

iTrader: (4)

so you have checked all over nothins lose??
get a stepthascope and prode around the engine see if you can locate the sound maybe it's not the engine could be mounts....

have you ever held it at 8 grand to much?

now im not saying this could be the same but i heard a knocking sound coming from my engine i thought somthin got into the flywheel area..
the car ran fine as if it were normal i tore the engine down and the rear rotor bearing welded to the eshaft. and yes it was my fault i was doing cookies 4 times a week for 3months perfecting my skill

Rogue_Wulff

Only time I ever heard a noise like that in a rotary, it had spun a rotor bearing and the rotor was slapping the side housings.

Kentetsu

Thanks for the suggestions guys, but the noise is too loud to be bearing related. The sound seems to be coming from either the intake or exhaut. I think the most likely idea is that I have a cracked apex seal, or maybe lost a corner seal or something. The odd part is that it is only when the secondaries open. I mean, its like an on/off switch...

Man in Black is going to stop by tomorrow and take a listen. But I really can't imagine any explanation for this that doesn't involve a terminal motor issue.

blwfly

iTrader: (4)

if you think a apex is brokin do a getto compression test and that will help anwser that theroy..

another thing will be to drain the oil out and drop the oil pan..
that is the best way to see if bearings are gone you will have metal flakes on the pan and that my friend is heartbreaking "what i found on my engine"

i removed the engine and checked the stat gears could see exsessive wear and groving..

ray green

iTrader: (14)

Wait, I did have a sound like that once, I tought it was something falling apart in the engine. Not directly connected to the secondaries like your problem, but it did come and go with the throttle and it was impossible to figure out where it was coming from. Turned out to be the power steering box crapping out.

Most likely wrong, your GS probably doesn't even have power steering, but some wishful thinking at least.

Ray

dbragg

iTrader: (7)

does it kind of sound like ball bearings moving around? i have heard two metal like noises from 12a. one from my daily driver is a gringing like noise that im 99% sure is from the shot AC compressor. it didnt do it at all while the belt was off of it but did it again when i put the belt back on.

another is from a 12a my friend owned, then another friend owned, and now i own. it has 60-70K on it. when it was in its original car it would sound like that when it got warm or something. the car ran a 15.3 in the 1/4 with a stock port and bolt ons. after that run though and it was heated up itd start making the noise in the higher rpms/full throttle and the car would feel slugish at the same time. since then the car was sold from that friend to my neighbor and he drove it for months without any issues. i know own the engine and its strong as can be. i dont know if it was timing related, fuel related, or what. im pretty sure it doesnt do it anymore.

t_g_farrell

iTrader: (1)

Maybe it's just detonation for some reason. I know its not turboed but maybe, like one the other post suggested, when you open the secondaries some fuel bleeds into the exhaust and its burning up right at the header. I would expect the header to be glowing red as this happens though. Just a wild *** guess.

I hope its not a bearing issue, good luck.

Kentetsu

Thanks again for the ideas guys. The only external belt driven component on my car is the alternator (and water pump), so the sound is definitely coming from the motor.

It does not sound bearing related, nor is there any relation to the rpms of the engine. The noise appears to be coming either from the exhaust header, or the intake area.

I have already eliminated the possibility of detonation by enriching the carb, and retarding the timing. This resulted in no change at all.

Rogue_Wulff

The engine I tore apart that made a sound like that, had the rotor tips ate up at both ends. The Apex seals were about 3mm shorter than the were just a few miles earlier, and the side seals/corner seals were toasted as well.
It still ran fine below about 3500, but above that, it sounded horrible. The bearing just fell outta the rotor when I took it out of the engine.
Definatly does not sound good. Drain the oil thru a screen, and look for copper colored bits.

SSRx7

While I don't know a whole lot about rotaries, I do know engines. And if a major part was broken internally, you could tell as the rpms raised or lowered.

In this case, he said that he could take it all the way to red line on primaries and not hear a thing. But tip the secondaries at any rpm including idle, it instantly starts making the noise.

I would check the carb for loose butterflies. It has to be something to do with the air flow as the secondaries are opened. Pop the carb off and look for loose/broken parts. Also check the intake runners for a peice of debris of some kind.

Later,
Bill

Kentetsu

The most likely sounding theory that I've heard so far is a failing seal (apex, or side seal). When the combustion pressures exceed a certain point, they escape into the adjacent chamber. Then, they would either escape into the exhaust header or go the other direction and head into the intake. I believe that this is what's happening.

I can't really bitch too much, since I've run her very hard over the last few years. I think it was very considerate of her to give me a "two weeks notice" before completely blowing up...

vipernicus42

iTrader: (4)

Have you checked the wire you used to wire up your secondaries?

If it was broken, the secondaries would still stay closed for a good while, but when you pushed "into" the secondaries, they'd thwap back and forth with the pulses of the air since the rod is not being held in a specific place by the wire...

It's a long shot, a shot in the dark at best, but it's my guess.

Jon

Kentetsu

Thanks for the idea Jon, but the carb has a solid linkage on it (Sterling) and is working correctly. I watched inside the carb while working the linkage, and the secondaries are functioning perfectly. I wish it was something simple like that...

ray green

iTrader: (14)

How 'bout this?

Don't worry about it until it breaks?

I've had a few go away that way.

Ray

Kentetsu

lol, well that's a thought I guess. The only problem is, some of my races are over a hundred miles away, and I don't trailer the car. This is sort of a matter of pride for me, being able to drive my race car to the event and then home again. I love passing the trailer queens on the freeway after having stomped them at the races. I also drive the car to/from work usually.

Kentetsu

Well, it just started last Friday. It was about 70 miles on the freeway, and I think we were averaging about 90 mph. When I pulled into Lansing and rolled the windows down, that's when I noticed it. There has been no change since then, even after racing it all day Saturday. I told myself I would take it easy on her for the races, but damn if I've got any self control...

On the other hand, I think it will be interesting when I finally tear this poor thing down and inspect it. It will be cool to see what that many miles looks like on the internals, and what kind of shape it was really in. I've known for some time that my compression is lacking, most likely due to nothing more than the miles on it, but wanted to see how long she would go.

I also want to see how clean everything is, since I'm an avid user of Seafoam. When I finally do this, I'll be sure to post up the pictures.

As far as my plans go right now, I'm leaning toward a 13b in conjunction with my Sterling carb. Should be a nice change from my tired old 12a. At least this is happening just a few weeks away from my yearly bonus. lol. Wheels and race rubber may have to wait until next year though...

zaridar

iTrader: (3)

This may sound stupid but i was messing around with my timing and the distributor cap i heard a knocking noise. it turns out the metal shield or whatever in the distributor under the rotor was not seated in the groove. I thought i blew my new engine up but it was just that. easy fix. might be worth a shot. cant hurt anything?

blwfly

iTrader: (4)

^^ that and a rotor cap not seated right will cause that.. "had to buy a newone was all chipped up.."

Kentetsu

Yeah, I wish it was that simple. I already learned my lesson on the dizzy cap the hard way a couple of years back... I'm going to take another hard look at it tomorrow after work. But I've already done that a few times, so I'm not expecting any miracles.

On the other hand, keep the ideas coming because you never know when I might miss something stupid and obvious..

2Lucky2tha7

iTrader: (3)

I'm gonna have to go with "spun" rotor bearing, from my experience. This happened to me over 2 years ago, and I was able to drive with a spun bearing for about 2 weeks before I finally couldn't take the loss of power anymore and I pulled the engine out and tore it apart to find out that my rear rotor bearing had seized to the eccentric shaft and the only movement was between the bearing and the rotor. Pretty crazy. I couldn't believe how long it lasted like that. It sounded like something similar to a rod knock, especially if I tapped the throttle wide open. It was really bad. This was a 13B by the way.
So for now, I recommend draining the oil and opening up the oil filter and check to see if the oil is "shiny". For the most part, that should give you your answer.
Brian

Bruceman

iTrader: (5)

Sorry to hear about your engine problem. Must be time to do some porting!