I my engine fixing to blow........................

[Guest]

I, as you all know, have finally gotten my car running. So far, so good. That said, I had been running the engine, before the cam loss, at 8*BTDC, using centrifugal advance, no vacuum. I retimed the engine after the initial cam break in and it won't idle at that setting, I gotta run it all the way out to about 15+* BTDC to get a good idle, which it does. At speed it is strong, although I haven't revved it much over 3K rpm yet. Did I dial my cam in wrong to have to run it at this setting. Now, I did send the damper off to Damper Dudes and what they sent back was a damper that was set perfectly at TDC on the first cylinder. Maybe my old damper setting was off. I have heard of some having to run centrifugal advance settings at this setting, 15*. It all seems ok. It is possible that I dialed the cam in wrong. Like I am gonna break it all down and change that. This is not the real problem. When I drop below idle, like when the engine is bogging or choking down while parked, there is still that awful chugging noise noise coming out of the small block somewhere. I Plastigauged most of my crank and rod bearings and they are to spec. If I gun it and bring it back to idle, this goes away, and at speed, it runs happy as can be. I really, really don't want to pull a Brosky and pull the engine for a premium rebuild. I just want to drive my car.

I really don't think I am trying to throw a rod or anything that horrible. Just part of having a modified engine, I hope.

Any encouragement out there is appreciated.

 

[Brosky]

Re: I my engine fixing to blow....................

Bill,

Let's start from the beginning with the initial 8*BTDC. That was too low, even by conservative Triumph specs. 10-12* BTDC is the starting norm and then all of the other variables start to kick in, but I digress. If your old damper was off 2-4*, you are now pretty close to being where you are now, so let's assume that it was off, or you would have had a real pig before at 8* and I know that was not the case.

Now here we are today and your at 15* BTDC. Guess what, so am I!! Not for any other reason than mine idles best (850-900RPMS) and runs smoothest there with the higher compression and TH5 cam. I can lug it down to 1,200RPM in 4th gear on a level road and just give it the gas and it rev's right back up again without a ping or chugging. So I'd say you're fine with things the way they are timed.

If you were going to throw a rod, it would have happened already nd we'd be reading the for sale ad now, so that's not gonna happen unless you try for red line for 2-3 minutes this time.

I'm not sure about any other noise, (because I can't hear it) but what do you mean about "choking down when parked"? You're not shutting it off via the old "clutch out and brake on in gear" method are you?

If so, that's gotta come to an abrupt halt.

 

[jessebogan]

Re: I my engine fixing to blow....................

Ok Bill, don't panic!!. Check the total advance. If your timing light, or the damper markings can't do it as is, borrow a light with advance capabilities. The full advance should be all in by 3500-4000 RPM. (maybe sooner, depends on advance curve in the distributor) Set the total advance to around 36 degrees, and let the idle advance fall where it may. You can experiment with that a little, but 36 degrees seems to be enough. Just make sure you get no pinging under load. Part of the deal with a "hot" cam is that the cylinder filling at low RPM is not great, making the "effective" compression ratio lower than the "mechanical" ratio. More advance than you are used to seeing helps bypass this effect, and helps the car make decent power. You can't really hear hi speed detonation, so that is why most folks say keep the advance at high RPM limited to around 36 degrees. Clear as mud? Classic Motorsports magazine in the last issue or two has an article on "camming" an MGB, and they explain it all pretty well, better than my chicken scratchings I am sure.

 

[Brosky]

Re: I my engine fixing to blow....................

You are correct Jesse. It takes a very trained ear to hear detonation at high speed (engine RPM's that is, more so than road speed). That's why most dyno operators stand very close to the engine and driver to be able to hear it as well as shut it down before disaster strikes.

I've been very fortunate for all of the years of working in noisy shops to have great hearing for very slightest of background noises. Sometimes it's a bit of a curse, but still a blessing. I can hear pinging that others can't, so I was always the test driver for problem cars. Of course, I also hear EVERY squeak and rattle, so that's the bad side of it.

My current distributor is set for a total mechanical advance of 35-36 degrees at about 3,800RPM's. It runs great and I have no detonation using 91 octane fuel.

I have a few others with a bit different curve(s), but those will come out after a few thousand more miles on the new engine.

 

[RonMacPherson]

Re: I my engine fixing to blow....................

Paul covered a very important caveat. High octane fuel.

If you're going to have the total advance on 36 degrees, especially with one where the compression is raised, you need hi octane fuel.

For todays ethanol diluted fuel systems you might be better backing it off to 34 total.

Ideally when the engine is dynoed they can take temp readings and correlate total advance by temp spikes. Boy a detonation sensor would be nice on these, but....


And they did give you the most important advice, focus on
total advance and let idle timing fall where it may.

 

[Brosky]

Re: I my engine fixing to blow....................

Ron,

I'm just lucky that it falls the way it does.

Well, then again maybe I'm not. That's the way that Jeff set up the curve at Advanced Distributors based on what I told him I was building, so I guess that it's only lucky that I know about his services.

I've never run anything but the highest octane that I could get in the car. Overkill, maybe, but it made me happy.

 

[poolboy]

Re: I my engine fixing to blow....................

'morning, Bill. Sunday. Looks like it's going to be a hot one..low 90's.
Anyway, I was out for a drive this morning before it got too hot and thought about that knock that you were hearing.
This may have already been put out there, but if not, I remember having a noise in a VW engine that had me baffled to the point that I took the engine down to find out what the heck it was.
Turned out to be a wrist pin a little loose in the connecting rod.
Just wanted to put that out for your consideration.
Other than that, how's things going? Jeff asks about you.

 

[TheSearcherMan]

Re: I my engine fixing to blow....................

Its impossible to say what the noise is without hearing it. What is the oil pressure when it is making the noise? Pull the plug wires one at a time and see if the noise goes away. If it is serious it will get worse, rather rapidly. Be prepared to pull the engine down again. The longer you run it, if it is serious, the more cleanup and damage you will do to the good parts.

 

[AltaKnight]

Re: I my engine fixing to blow....................

Bill.....
I just installed a hotter cam TH5 from BPNW (same as Brosky's)
It idled very poorly and I suspected I'd managed to dial mine in incorrectly.
So here's the simple test that you can do to check it before ripping it apart again as I had to do.

1) reset the valve clearances on # 6 cylinder ie the 11 and 12 valves to 120 thou while the tappet is on the cam base circle, be accurate with this.
2)Set it accurately at #1 TDC top of the compression stroke (be aware your damper marks may not be correct)
3)Check the valve clearances on 11 & 12, they should measure the same clearance (roughly 16 thou on mine) but the measurement is not important, they just should be the same or darn close anyway.

When I did this test I found the intake valve (#11) was partially open and had no clearance at all; that's when I resigned myself to tearing out the radiator etc to retime the valves, got it spot on the second time.

 

[sp53]

Re: I my engine fixing to blow....................

I would perhaps look at the possibility that the infamous noise is the crankshaft slapping back and forth. You might even be able to fix that by just pulling the pan and popping out the thrust washers. I do not know for sure. If not that, when you had the rods out did you have them trued. I mean did you blot the caps and rods temporarily together to torque specs without the bearings in and then have hole trued out to be perfectly rounded because the rod hole can become egg shaped, permitting extra room for the new bearings. I would imagine you did that but just checking. I doubt if it is a wrist pin because they would have been honed to fit.