Obviously, I'll find out for sure when I tear into it further but, here's what's going on. I was on a speedster rally in St. Louis, MO last weekend. When climbing hills or accelerating I got clatter/rattle noise coming from up front. Not a heavy sound like a rod knock and not at a regular beat, like thump - thump - thump. More of a random clatter. When going downhill, I could do 45 plus with no noise at all, but once I opened the throttle: clatter.
Now that I'm home and just getting into it, it appears that the noise is coming from the timing gear, which is bronze. However, the gear is nearly new, and looks it. It has acceptable backlash although probably more than "blueprint" but not ridiculous. The cam bearings are nearly new as is the Stipe cam. It's not endplay noise as it has a Bosch front plate that adjusts the end play out of it.
My theory is, the front main bearing is bad, allowing the front of the crankshaft to vibrate up and down like a tuning fork and causing the crank gear to clatter/hammer away on the bronze cam gear.
Got called away before I could finish my posting above.
So, does the above theory sound plausible and have any of you experienced this very thing, with the front main allowing the crank shaft gear to hammer away on the cam gear?
As I learn more I'll let you know.
Jerry, The rear main has the thrust surface that keeps the lateral movement of the crankshaft in specs. Could that surface be worn where going up hill the crankshaft moves rearward which changes the mating of the gear teeth, then going down hill the crankshaft moves forward where the teeth on the gears once again mesh better? Just a guess on my part.
Bad bearing in the generator?
I checked crankshaft end play, it's o.k.
I thought of that and ran it with the generator removed. Still clatters under load.
I also pushed off the fan belt to get the fan, (and "w.p."), out of the equation. My crank pulley is the clamp-on aluminum type and is tight.
Heavy thumping on load is usually a bad main bearing. A chatter under load could be a number of things. Have you pulled the cam in and out to see if it is moving? Also check for piston play, it could be piston slap.
Jerry, can you post some pix of the speedster rally. Steve
I would love to but I didn't take any.
Scott Stier posted the following on the MTFCI forum. I haven't tried it but maybe there's some good pics there. "
"We're adding more pics to our Facebook page, search for Speedster Rally, we're one of the two."
All end play has been adjusted out of the cam using the adjustment on the Bosch front plate.
What condition is the front fan pulley?
Loose cam gear nut??
Jerry, don't ask me how I know that some of the new cam bearings being offered are undersized in the block tunnels, by as much as .012". You can check this with the timer off and a block of wood and a lever. The valve train will push the cam assembly downwards in the block. Use the wood block as a fulcrum and lever upwards on the snout of the cam. If your bearing is good, you will have no movement.
This may help.
Allan from down under.
Well, when I installed the Stipe cam I also bought new cam bearings. The new bearings had more clearance/slop both on I.D.'s & O.D.'s than my old ones. I used the old bearings which were excellent.
The pulley is the clamp-on aluminum style and is tight.
Hoping to get into it a little deeper tonight. I'll keep you all posted. Thanks for the ideas!
I vote for a loose rod bearing or maybe something simple like a loose front engine mount.
Most likely a rod bearing as it starts up when throttling up. no.2 main take most of the abuse when it comes to checking mains, you will usually fell them through the floor boards. KB
"When going downhill, I could do 45 plus with no noise at all, but once I opened the throttle: clatter."
If you mean that you closed the throttle and you heard the "clatter", then it sounds like a rod bearing.
No, as I stated, "... once I opened the throttle: clatter." It makes noise only under power, not with the throttle closed.
Here's an update.
I removed most of the "stuff" from the front of the motor and put a dial indicator on the crankshaft end, right next to the timing gear. I pried up on the crank end and was able to raise the crank .012. I could also push it down about .005.
I believe my original theory is correct. My front main bearing is shot and it was allowing the crankshaft to vibrate up & down while under power and causing the crank gear to rattle on the bronze cam gear. The engine is now out of the car but no yet disassembled.
Jerry, you confused me when you said that you did 45 MPH downhill and then opened the throttle.
I wonder if your oil tube is broken or the funnel fell off. Or perhaps a plugged oil tube caused the front main to go out?
If your measurements are correct, I would say, the front main bearing is bad or needs adjustment. If you still have shims in it, you could drop the cap and pull out the shims and see if it will tighten enough. I don't think you can see in well enough to determine the condition of the babbit unless you pull the engine and crankcase.
Confusing people is what I do best! Sorry about that. Thanks!
Excellent point. I will check those items. I've never had any babbitt bearing go bad, but the last one I expected was a front main.
I have a new SCAT crank I've been itching to use when the time was right. I think the right time is right now. As you mention, I would worry about the condition of the babbitt where I can't see it, (in the block), if I were to just try an adjustment.
Thanks everyone, I'll keep you posted on what more I find.
Finally got deeper into the engine. In 2003 I broke a fiber timing gear. Ever since, the engine just didn't seem "right" but it ran well and I put several thousand miles on it since. Well, once the hogshead was removed, I looked into the oil tube funnel and saw something obstructing the opening maybe 80% - 90%. I fished out the "something" and discovered it was a fiber timing gear tooth that neatly fit into the oil tube. The accessory outside line must have kept it going all these years but, in the long run, it wasn't quite enough.
Off to the "rebabbitter"!
Fiber timing gear wrecks another day. Those things are a curse.