Top End Noob

[niclpnut]

Have access to a compressor/leakdown tester? Think the leak down tester is available as a loaner tool from most autoparts stores.

Use the tool and isolate where your compression leak is coming from.

Nic

Bumping with a "progress" report.

I never could get the No. cylinder to fire. Plugs looked dry, so I tore down the carbs and dipped them again. Sprayed out every passage, and they look completely clear. The compression in that cylinder is lower than the other three, so perhaps it is not generating enough vacuum to pull in fuel. There is gas in the floats, so it's getting to the carbs.

Otherwise, I still have my spark insulation theory, but dry plugs probably strike that out. At this point, my plan is:

Do one more compression test dry, then wet, to see if No. 3's problems are piston rings or valves. This will determine how far I go back into the beast. If the test show ring problems, I will double check that the rings did not get out of line (i.e., the gaps fell out of staggered position) when I reinstalled the pistons into the jugs.

Even if the tests show valve problems, that second cylinder head is cleaning up to be much better than my original (no spark plug thread insert, nice looking valves/seats), so it's going on the bike either way.

Just hoping that the compression problem is valves not rings. I have fresh base and head gaskets for each stage, just in case.

We'll see.

Guess I need to hold a seance or something. Cripes.

I don't think blue loctite is your problem. Most of the contact between the insert and head should still be metal to metal.

I have an odd theory on the No. 3 cylinder. Tell me if this makes sense.

Recall that I have spark, low but enough compression and fuel flow, but no firing on that cylinder.

When I pull the No. 3 and plug and ground it against the engine, it sparks fine. Also, the No. 2 cylinder is running, so the coils and ignition are not the problem. After beating my head against a wall, the spark plug insert came to mind. The instructions for the plug insert said to use blue loctite to secure the new threads, so I did. Is it possible that the loctite is causing the plug to not ground well? Is loctite conductive? If I used too much of the stuff, or should not have use it at all, could this be blocking that cylinder from getting a good spark?

If this theory craps out, then I am out of ideas. OTOH, if the loctite is the villain, I already have a head to swap out (and it looks better than my original so far), so I can commit to that as a fix.

OK that No. 3 cylinder is possessed. Checked the plug grounded against the frame, and it's getting spark. The float bowl has fuel. But that pipe is cold.

New compression test shows improvement, but No. 3 is still out of step. 120/120/90/120

So fuel, spark and some compression but No. 3 gives me the bird. What the hell?

[Nessism]

Sounds like #3 isn't firing. I'd check for spark first.

Yowsa! That new head came in and it looks pretty sweet. The valves and seats are in great shape, just need to clean off some carbon. Dropped the valves into some Berryman's and am very tempted to go ahead and swap heads.

Did some more fiddling with the idle. It is running, but not great. Plugs looked a little sooty, so I backed out the air screws a little. That helped some.

My chief concern on the idle so far is that the No. 3 exhaust header is much cooler than the others. Not ice cold, so I think it is firing. But it only feels warm, not yank your hand away hot like the other three pipes. The exhaust also is backfiring/popping at the tail pipe. Will continue to fiddle.

I'd say after 2-300 miles you should see your numbers improve. Maybe not even that long. Don't baby it!

Repairing spark plug threads has been done before with the head in place. There's advice there about controlling debris from the drilling. Try some forum searches.

I already repaired those threads, but the lower compression in that cylinder relative to the others makes me think that repair might be losing compression, leaky, etc.

I'd say after 2-300 miles you should see your numbers improve. Maybe not even that long. Don't baby it!

Repairing spark plug threads has been done before with the head in place. There's advice there about controlling debris from the drilling. Try some forum searches.

Did you replace the intake boot O-rings yet? If not, you need to otherwise you can get vacuum leaks.

One other thing you should do is torque the cylinder head again after you put a few heat cycles on the engine. Do NOT skip this step otherwise you can get leaks. Also, check the valve clearances again.

Yes, I replaced the intake boot o-rings and fasteners with fresh rubber and SS allen-heads from cycle o-rings. I also replaced all the carb o-rings with a set from Barr. Just in case, I have a full set of new carb rubber from Barr as a back up.

Thanks for the follow-up torque advice. I checked and adjusted the valve clearances when I put her back together. If I cannot get the idle sorted, I can go back to those valve clearances. Between my old spares, some club shims and the parts on this new head, I am swimming in shims. Once the thing is running, I will hook the club up with plenty.

Follow up question.

I understand that cold compression numbers tend to be low, and that new rings and jug hones will take time to settle in before compression will increase after use.

How long in terms of miles/running time before I should expect to see better compression results?

I just got a replacement head that may not be necessary if this rebuild settles into place. OTOH, if that No. 3 cylinder continues to show bad compression, it has to be that bad spark plug hole, since I have rebuilt/replace everything else. So I can clean up this second head and do another teardown, if I have to. I prefer to stick with the current build if possible, though.

[Nessism]

Did you replace the intake boot O-rings yet? If not, you need to otherwise you can get vacuum leaks.

One other thing you should do is torque the cylinder head again after you put a few heat cycles on the engine. Do NOT skip this step otherwise you can get leaks. Also, check the valve clearances again.

OK - the tach issue was very simple. Way back when I disconnected the tach cable, the actual cable slithered right out of the tube. Once I remembered that and snaked it back in, the tach works fine.

I suspect that is NOT how it is supposed to be, but I can work with the results for now.

Still getting some smoke when it idles, but it looks like its stuff burning off the pipes, especially underneath where the 4 header pipes join into the one tail pipe. I continue to scour for leaks to make sure that it is only old grime and not fresh oil drips from a leak.

Now I have to revisit the idle and mixture puzzles with these carbs. So far it seems to need choke to run, but the smoke investigation deters me from running the bike very long. The idle also wanders a bit, sometimes struggling to hold rpms unless I adjust the idle screw, but then creeping up too high.

I need to continue to fiddle with that to get her idling steadily, so I can set the fuel/air screws and synch.

Crap.

Looking at the service manual, it says to remove the tach drive gear when disassembling the head. I only disconnected the tach drive cable, because I am dumb.

I have not heard any grinding or other scary noises from the head, so hopefully the worm gears did not shred. Guess I will try hand-cranking to see if the tach spins or not, and remove the tach gear to inspect for damage, reinstall correctly, etc.

I swear Clymer (whom I trust less and less) only said to remove the tach cable. Ugh.