277 trouble

[pamcopete]

gggGary,

The engine has just been completely taken apart and had the cam shaft and crank shaft split in two and then welded back together. The timing mark for the rephased cylinder was scribed by hand using a degree wheel. We are talking about the relative timing between the cylinders, not the absolute or true timing of one cylinder vs the other by measuring on the crankshaft for a device that is mounted on the cam shaft and is subject to any slight misalignment in either the welded cam shaft or crank shaft or both, cumulative, against a hand drawn timing mark on the crank, and also subject to the timing chain. Despite all these vagarities, the difference nets out to 5 degrees which can be halved by splitting the difference, a common practice with points hence the relatively wide area of acceptable timing marks before and after the "F" mark.

In any event, even if the timing marks could be set perfectly, that does not mean that they are correct in the absolute sense due to the many variables as listed above.

In any event, he is focusing on the 5 degrees and he is adamant that he does not want to split the difference. At that point, there is nothing further that i can do for him and I had suggested that he return the PAMCO for a full refund and purchase another more suitable 277 ignition that has the adjustments he is looking for.

 

[gggGary]

Yes pete I get that. Hence my adjust one pickup. suggestion. AFAIK The Crank is not "cut" on a 277 engine, the existing splines are used to change the relation between the cylinders so the crank degrees "between cylinders" is pretty cut and dried. Crank "alignment" could be an issue, but that that would manifest pretty quickly. All of the various cam re-index operations do have room for variables and the the individual cam lobes should be degree'd to rule out an issue there.

I'm just kibitzing and trying to find areas of agreement. As I said above I also think 5 degrees of timing is unlikely to show up as a cold cylinder, more like a slight difference in power output. Yes it's frustrating when one of the parties skips answering a question! Has a compression test been done recently? IE rechecked after the cold cylinder was noticed? Fixating on one item in a complex system when troubleshooting is a common human foible, how many times have I done that? An example is the "carbs are new can't be them.... Pete's I'll give your money back offer is very fair and reasonable. With all the new things on this build some teething is inevitable hope to hear how this gets resolved eventually.

 

[McGyver62]

will find out all answers next week when i see my mechanic , as for the compression there is plenty of that it was tested

 

[pamcopete]

gggGary,

Small point, but I know that the crank is split and rejoined on the splines, but HHB does weld it for as he says, high speed integrity and he checks for any alignment issues, implying that there could be alignment issues.

My basic point here is that with all the variables, there is not much point in adjusting for perfect timing as you really have no way of determining if in fact it is absolutely perfect or just appears to be perfect. 5 degrees split between the cylinders is 2.5 degrees at idle, but the more important timing is at full advance where the engine spends most of its time, so if the 5 degrees holds true at 40 degrees of full advance, then one cylinder will be at 38 degrees and the other will be at 42 degrees, and as you have noted, you would not be able to tell the difference.

I did develop an E-Advancer 277 ignition and it was beta tested successfully, but subsequent field testing revealed that it was difficult to install as the basic 277 system has 16 different ways to install it, with only one being the correct way, so adding another variable would make it 32 different ways to install it, so I decided to not offer it, although it worked great and did provide separate movement of both sensors as the transistor was in the E-Advancer and did not impede the movement of the sensor boards. So, we are having a back and forth here with the basic 277 ignition that has actually been going on for a week in PM's all over 2.5 degrees and only 16 different ways to install it, so you can perhaps read between the lines here as to my enthusiasm to offer a more complicated system. There are other 277 ignitions available that do offer not only complete and separate adjustment of each cylinder, but have programmable advance curves, rev limiters, blinking LEDS etc. I offer a basic 277 ignition for $119.95 that gets the job done.

 

[pamcopete]

will find out all answers next week when i see my mechanic , as for the compression there is plenty of that it was tested

So, you don't know if the timing was set TDC or BTDC?

 

[TwoManyXS1Bs]

Since the Pamco rotor doesn't have the drag resistance provided by points followers, it is free to oscillate/wander within the confines of the clearances of the advancer mechanism, and 2°-3° is easy to get within slightly worn weight ears and slotted disc. The varying angular velocity of the crank/cam provides the oscillation.

A simple test would be to observe ignition timing with a timing light, then apply light drag friction to the Pamco rotor edge with a finger, and see if timing changes. Same drag test, with finger on rotor face, would eliminate end play influence.

Just guessing here, does 0.005" of FET misalignment translate to 1° of crank position?

 

[pamcopete]

TwoMany,

At idle, the springs in the mechanical advancer hold the rotor to the cam shaft surprisingly well. On the way to full advance, there may be some tendency to oscillate due to the slowing of the cam on the up side of the lobes, and a speeding up of the cam on the down slope, but it is the same for both cylinders and the discussion is all about the relative timing between the two cylinders. Once the advance has reached full advance, it is once again locked to the cam and my contention is that is more important than at idle. The in between is just 3,000 - 1,500 = 1,500 RPM's.

The oscillations of the cam shaft due to the slope of the cam lobes is one of the reasons that I do not offer an E-Advancer for the PAMCO CB750, 550, 500, 350F and 400F bikes because they are crank based and the crank is much more stable than the cam so the mechanical advancer on these bikes are not impacted by the oscillations of the cam based systems and they are in factory new condition even when 40 years old.

www.cb750ignition.com

 

[McGyver62]

I'm calling it TDC in reference to where it should fire i will verify the BTDC setting your asking about with jim next week when i see him . No big rush to ride now as we are pulling out our dog sleds and reinforcing our igloos at this time of year

 

[pamcopete]

I'm calling it TDC in reference to where it should fire i will verify the BTDC setting your asking about with jim next week when i see him

OK. Also ask him what type of timing light he is using as the timing lights with a preset advance feature are not suitable for use in a motorcycle.

 

[McGyver62]

he has been running a successful motorcycle repair business with dyno and fully equiped machine shop since 1981 I'm thinking he may have the thingy you mentioned

 

[member3480]

OK don't have much experience with the 277 stuff but maybe this may help. I built a race motor for someone and all the parts came from him and I could not get the timing right to save my ass I was 8 degrees out no matter what I did. Went over motor with degree wheel and I was using electronic ignition that pickups could not be moved. Now I had slotted cam gears and they were all the way to one side and cam just didn't look right to me. So I knew something was junk but didn't know if it was crank or cam and both came from good places. So this is what I did to prove to myself and owner it was one of his parts. I cut more out of the cam slots and got it down to be out 3 degrees and run and fire where it should. Now cannot race bike like this and he sent cam and crank back to vendor and got replacement parts and it went together perfect. So my bet was on crank when taken apart was not put back correct. When doing 277 both crank and cam are cut and put back together . I would think one of those are the problem not the Pamco. See if someone has a 277 cam that you could try to say its not the cam.
Good luck going to keep reading this is interesting

 

[DIRTY DOG]

I have done a few 277*rephased eng. now and the pamco has been great and dead on,
1st ,what are you running for charging system PMA or the stock rotor ? if it pma then make sure you've marked TDC at TDC,and the rotor is tight as they will move with out a key to hold them been there done that...
2nd, is it 5*between cyl's (sorry if I missed that part ) then split the timming has been done for years, but if thats not good enough them build your own points plate,http://www.650motorcycles.com/277ign.html,and them you can set each cyl dead ball's on.
,3rd 100* between cyl is most likely carb's or a vacuum leak ( in most case's not all the time), but here is what I would do; redo every thing,reset the crank TDC redegree the cam(and make sure your doing for an xs650 not a small block chevy (they are diffrent I found out the hard way ),reset the cam chain ten reset the valve adj., 2 new spark plugs, recheck the compression and make sure both are the same ( could have a valve leaking) recheck the carbs inside and out and retest
redo it don't assume it's right cause you checked already it's probley a simple fix,some time we try to hard ( I have been a GM tech for over 35 years and some times the new kidd finds the problem cause we are looking to hard for the fix ) good luck and keep us up dated

 

[McGyver62]

Thanks Dirty Dog

 

[McGyver62]

Thanks for the help guys mechanic solved that problem by modifying the plate

 

[gggGary]

gotta see a close up of the modified plate!

 

[McGyver62]

he told me he slotted it .sorry lol