Top End Noob

[7981GS]

Update:

Got the cylinder head on and the chain timed. That took three attempts because I am dumb.

Checked the new valve clearances, and two of them are too tight. So I am waiting on some new shims.

Put the exhaust back on, but ran into some trouble there. Basically, some of the exhaust bolts do not like the threads on that head. They came out of the head without much difficulty, but when I reinstalled the pipes, 2-3 of the bolts get really tight early. I checked the bolts, and their threads look fine. So I fear that the head has gotten cross-threaded or something.

After pairing the bolts as best I could, the exhaust is on there, but I cannot properly torque some of the bolts for fear of further damaging the threads on that head.

Any ideas? Do I need to bore out those threads?

Just re-tap the holes. You should be able to go in 24-25mm.

Daniel

 

[MisterCinders]

Top end is rebuilt. Now I need to change the oil, re-install the carbs, add some fuel and start her up.

Then I will figure out what else is wrong with the bike no doubt.

 

[MisterCinders]

Just re-tap the holes. You should be able to go in 24-25mm.

Daniel

Would I tap in at the same bolt size or go bigger to clear out any stripped/crossed threads?

I am a tapping virgin, so be gentle.

 

[mike_of_bbg]

Same tap, you're just cleaning up the threads. Make sure you use anti-seize when you put the bolts back in.

Would I tap in at the same bolt size or go bigger to clear out any stripped/crossed threads?

I am a tapping virgin, so be gentle.

 

[7981GS]

Would I tap in at the same bolt size or go bigger to clear out any stripped/crossed threads?

I am a tapping virgin, so be gentle.

Use oil on the clean tap when you go in, clean the tap and the cleaned up holes with brake cleaner and compressed air to remove the debris on each hole and anti-seize on the clean bolts or studs that you install.

Daniel

 

[MisterCinders]

Great.

I got the top end rebuilt, valve clearances into spec, carbs fixed and installed, Dyna ignition into place, and the damn thing still won't start.

The starter motor turned fine, but it would not catch. Spark and battery were good. So I checked compression. It sucked. About 30 psi across the cylinders.

So I pulled the valve cover again. Lo and behold, my timing was way off.

At this point I can redo the timing, though I have no idea how it got thrown off. Given that I have hand cranked the motor and turned it with the starter several times trying to start it, what are the odds that I have bent valves in the process. I really don't want to pull the head again. Is there a way to check for bent valves without actually pulling them out again?

 

[Nessism]

If the valves are bent your valve clearances will be really big because the valve won't close. Hope this isn't the case after all you've been though with this engine.

 

[MisterCinders]

I'll watch those clearances then. Fingers crossed.

 

[gearhead13]

If you hand cranked the engine before turning it with the starter, you would have noticed (hopefully) that it got real hard to turn and didnt turn it anymore. Reset (and doublecheck) the timing, and do another compression test, AFTER you hand crank it.
You could do a leakdown test with the cams out if you had a leakdown tester.

 

[MisterCinders]

If you hand cranked the engine before turning it with the starter, you would have noticed (hopefully) that it got real hard to turn and didnt turn it anymore. Reset (and doublecheck) the timing, and do another compression test, AFTER you hand crank it.
You could do a leakdown test with the cams out if you had a leakdown tester.

There were some stiff patches in the hand-cranking, but I figured that to be part of the rebuilt pistons settling in, etc.

I have the camshafts loose now, and will redo the timing tonight. In anticipation, though, I need to solve the mystery of how the timing got out of whack.

I religiously followed the timing process, used a vice-grip to secure the shaft before securing the bearing caps. There was no doubt in my mind that the timing was right. Nevertheless, when I pulled the cover last night, the timing wasn't just off, it was way the hell off (like 30-40 degrees).

How the hell can that happen?

One variable comes to mind, but I don't see how it could play a role. Namely, after setting everything in the head and buttoning that up, I went ahead and replaced the ignition with a Dyna-S unit. Off course, that required removal of the advance governor, which is one part of the timing equation. I reinstalled that with the notch in the correct position though, so I can't believe that would shift the timing (e.g., by moving the advance marks out of position). If that were the culprit, my compression would be OK, but the ignition timing would be hosed.

So I welcome any guidance for retracing my steps and getting it right this time. If I have to f**k with the actual valves again and replace them, cut new seats, etc., my head will explode.

 

[MisterCinders]

Cripes, having looked over other threads about this scenario, I am not liking my chances on these valves. In most of them, people note "just don't hit the starter button." Of course I found the problem after several hits on that button.

FML

 

[mike_of_bbg]

Like Ed said, check the valve clearances. They should be very large if you bent the valves because they won't close.

I'd take the fact that you're getting 30 psi on a cold motor with the timing way off as a good sign - if your valves were bent you probably wouldn't get that.

 

[MisterCinders]

OK - mentally prepping for tearing into this tonight, and trying to figure out how I f**ked up the timing before.

When I set the chain, I used the vice-grips to secure the exhaust cam while fastening the bearing caps. Then I counted off 20 pins between 2 and 3 and did the same thing for the intake shaft, including the vice-grips trick. I see the vice-grips in guides for the exhaust cam, but not the intake cam. Although it seemed logical to me, could that have thrown off the timing somehow?

 

[Nessism]

OK - mentally prepping for tearing into this tonight, and trying to figure out how I f**ked up the timing before.

When I set the chain, I used the vice-grips to secure the exhaust cam while fastening the bearing caps. Then I counted off 20 pins between 2 and 3 and did the same thing for the intake shaft, including the vice-grips trick. I see the vice-grips in guides for the exhaust cam, but not the intake cam. Although it seemed logical to me, could that have thrown off the timing somehow?

Okay so lets go over this one last time...

With cam chain tensioner removed...

- Set crank to 1-4 T mark.

- Pull up on the cam chain in the front of the engine to remove slack (but don't allow the crank to move) and then position it on the exhaust cam sprocket such that the 1-- mark on the sprocket aligns with the gasket surface. Clamp down on the cam with vise grips to lock it in place.

- Double check the 1-4 T mark to make sure it has not moved.

- Count 20 pins between the 2 and 3 marks on the cams and install the intake cam.

- Install and tighten the cam cap bolts, and remove the vise grips

- Wind up cam chain tensioner, lock the set screw, and install the tensioner in the back of the engine

- Loosen the cam chain tensioner set screw and listen for the plunger to spring out.

- Back out the set screw 1/4 turn open and reset the locknut.

- Double check the cam positions and 1-4 T mark with the tensioner released and turn the engine over a few turns using a 19 mm wrench on the RH crank end.

Crack a beer and call it good!

 

[MisterCinders]

Okay so lets go over this one last time...

With cam chain tensioner removed...

- Set crank to 1-4 T mark. Check

- Pull up on the cam chain in the front of the engine to remove slack (but don't allow the crank to move) and then position it on the exhaust cam sprocket such that the 1-- mark on the sprocket aligns with the gasket surface. Clamp down on the cam with vise grips to lock it in place. Check

- Double check the 1-4 T mark to make sure it has not moved. Check

- Count 20 pins between the 2 and 3 marks on the cams and install the intake cam. Check

- Install and tighten the cam cap bolts, and remove the vise grips Check. but see below.

Do you not have to secure the intake cam against the valves with grips? I thought the grips were to avoid stress on the bearing cap threads.

- Wind up cam chain tensioner, lock the set screw, and install the tensioner in the back of the engine

- Loosen the cam chain tensioner set screw and listen for the plunger to spring out.

- Back out the set screw 1/4 turn open and reset the locknut.

- Double check the cam positions and 1-4 T mark with the tensioner released and turn the engine over a few turns using a 19 mm wrench on the RH crank end.

OK - I did the tensioner later, after hand-turning the engine when checking clearances. That is how I screwed the pooch here.

Ugh.

 

[Nessism]

Do you not have to secure the intake cam against the valves with grips? I thought the grips were to avoid stress on the bearing cap threads.


OK - I did the tensioner later, after hand-turning the engine when checking clearances. That is how I screwed the pooch here.

Ugh.

Vise grips to hold down the cams are a good thing. Many people don't use them, but you are taking a risk with the cap threads then. I've done it both ways, but if you skip them you need to be careful to spread the load across all four of the screws on the cap (turn each a little at a time).

Guess you found out the hard way to never turn over the engine without the cam chain tensioner working. Hope you didn't bend any valves.

 

[MisterCinders]

Vise grips to hold down the cams are a good thing. Many people don't use them, but you are taking a risk with the cap threads then. I've done it both ways, but if you skip them you need to be careful to spread the load across all four of the screws on the cap (turn each a little at a time).

Guess you found out the hard way to never turn over the engine without the cam chain tensioner working. Hope you didn't bend any valves.

On the vice-grips, any reason not to use that method on both camshafts?

Hopefully this lesson is not too hard for me. At this point, I am definitely pulling the head to find out.

 

[Guest]

We are all out here rooting for you. You have a good quarterback watching over your efforts...
Curt

 

[MisterCinders]

You guys are going to make me cry.

Actually, if I destroyed those valves, there will be tears.

 

[mike_of_bbg]

There's no reason you can't use vice-grips on the intake. Definitely get that tensioner in there and released before you start turning the motor around!