Ready for Top End Rebuild

[Arclight88]

did you overlap the valve chain at the crank end?, that will jam it up

I'll check that again, but it did not appear to be last night. I am doing the rebuild with the motor base in the frame, and visibility is somewhat blocked. But I will check again...

 

[tritowns]

how did you check your ring gap? did you use a ring compressor?

 

[Arclight88]

how did you check your ring gap? did you use a ring compressor?

I placed the rings, one by one, into their respective cylinders about 1/2 inch (12mm) deep. I squared them into position using a piston and measured the ring gap.

I used my grandfathers old trick of using a piece of an old tape measure to as a wrapper to compress the rings as the cylinder block was slid over them (worked on the lawnmower I watched him work on once!) But I am sorely tempted to hit the NAPA store on the way home and spring for a real compressor.

 

[tritowns]

k, just wanted to make sure you did it right and it sounds like you did.

hell, ive used a hose clamp to compress the rings many times... use lots of oil, let it sit compressed for a short while and they almost wanna jump into those holes by themselves.

 

[Arclight88]

k, just wanted to make sure you did it right and it sounds like you did.

hell, ive used a hose clamp to compress the rings many times... use lots of oil, let it sit compressed for a short while and they almost wanna jump into those holes by themselves.

Interesting. I may just try the hose clamps (I've got those.) I will also give them a little time.

What has me concerned at the moment is the ancitipated mechanical resistance I will run into tapping the block off of the piston's if I indeed have a twisted ring. Should be some fun!

 

[tritowns]

just go slow... sounds like you've done everything right so far... i'm curious to hear what is causing the problem

 

[Arclight88]

First picture shows the cam chain not bound up in the engine base. Which told me it was time to pull the head.

Pulled the head no problem. Tried to pull the cylinder block up - nothin' doing!

Turned the crank bolt a little and the right piston rotated out of the cylinder, but the left piston was staying put. tried tapping on the base of the block with a dead fall and a 2-by-4, no joy. Used the torch on the cylinder skirt to loosen things up, still nothin'.

Time to get 'creative'. Cranked my motorcycle jack up to about 18-inches, and eased the crow-bar under the block to get some leverage, then drifted the piston out.

Damage to the left cylinder oil ring. Fortunately, I have another. Self inflicted wound here but I think I can recover.

More later...

 

[Greasey Fingers]

Great to hear you found the problem and its not too much of a drama!

 

[bcware]

I have placed the pistons in the barrels without any tools 3 times now. All I do is rotate the engine until both pistons are at equal height and oil the pistons and barrels. Next, I wrap shop towels around the base of each piston to keep them from falling to the side. I place the barrels on top of the pistons, supporting most of the weight with one hand. I use my free hand to position the piston vertically, to squeeze the rings, and to remove the shop towels once the pistons are in. Squeezing the rings by hand and giving the barrels a wiggle from side to side worked very well. Very little downward force is required.

 

[Arclight88]

I have placed the pistons in the barrels without any tools 3 times now. All I do is rotate the engine until both pistons are at equal height and oil the pistons and barrels. Next, I wrap shop towels around the base of each piston to keep them from falling to the side. I place the barrels on top of the pistons, supporting most of the weight with one hand. I use my free hand to position the piston vertically, to squeeze the rings, and to remove the shop towels once the pistons are in. Squeezing the rings by hand and giving the barrels a wiggle from side to side worked very well. Very little downward force is required.

Thanks, BC.

I used the hose clamp method and it worked well.

New issue to report. With the new rings in, the pistons turn through the cycle with the jugs in place. But when I bolt on head, the crank will only turn from 12 through 11-o-clock.

No amount of jiggling the cam chain makes any difference, and it does not appear to be binding on the crank shaft's cam chain sprocket. I have installed and removed the head three times tonight and the results are the same... no head it turns over as much as I want to turn it over. With head installed, only about 330-degrees of turn then it locks up.

I have made sure that the pistons were at the same level when the head was torqued down (per the book.)

I am a little mystified at this point. Please send your replies if you have solved this problem before or if you have an idea what to do next.

Thanks,

DJ

 

[drewpy]

is the cam installed?

if so did you time it? and did you fit the cam cover?

it could be the valve hitting the top of the piston

 

[bcware]

Yes, yes; we need to know how assembled the engine is when this problem occurs.

As per the manual:

Set the left cylinder to TDC
Place the cam so that the pip on the very end (where the points are) is at 12 o'clock
Place the sprocket on the chain and bolt it to the cam so that the pip on the sprocket is also at 12 o'clock
Rotate the engine to access the second bolt hole on the sprocket
Rotate the engine a few times and make sure that when the left cylinder is at TDC the pips are still at 12 o'clock

It is easy to be one tooth off because the tensioner and guide are not in at this point.

 

[Arclight88]

is the cam installed?

if so did you time it? and did you fit the cam cover?

it could be the valve hitting the top of the piston

The cam is not on the engine. The motor rotation is binding up with just the head installed and no valve actuation.

I had a discussion with a friend who has some experience in this arena about this problem. He reminded me that metal stretches and deforms due to use over time.

He wondered if by torquing the head acorn nuts to 23 ft-lbs (the range in book is about 21 to 24.5 ft-lbs) could be the issue. This is a motor that is just shy of 21K miles and is 32 years old. Even though it was running last week, it is possible that those nuts were not torqued within 'operational' specs at that point.

He suggested that I start with the working case (jugs only) and test for easy rotation. Then set the head on and test for rotation with nuts on only finger tight. Then add a few pounds to each nut in the cross-X pattern in pressure stages (10 ft-lbs, 15 ft-lbs, etc.) and check rotation at each stage. In this way, we can determine where the threshold for the amount of torque that the motor can permit rotation in its current configuration. Once that quantity is know, we can decide on the course of action.

Any thoughts?

 

[Arclight88]

Yes, yes; we need to know how assembled the engine is when this problem occurs.

As per the manual:

Set the left cylinder to TDC
Place the cam so that the pip on the very end (where the points are) is at 12 o'clock
Place the sprocket on the chain and bolt it to the cam so that the pip on the sprocket is also at 12 o'clock
Rotate the engine to access the second bolt hole on the sprocket
Rotate the engine a few times and make sure that when the left cylinder is at TDC the pips are still at 12 o'clock

It is easy to be one tooth off because the tensioner and guide are not in at this point.

Hi BC,

Just replied to Drewpy with a more complete SITREP. This problem is encountered before the cam is even in place.

 

[bcware]

Hm, I don't see how the torque on the acorn nuts is going to have any effect on rotation if the cam is not even on yet. The chain should be completely free and independent of the jugs. The only thing connecting the jugs to the lower sprocket is the piston rings and the friction on the jugs created by them.

So, before the jugs are on it rotates freely, but once they're on it binds? It seems more likely to me, that when you're placing the chain through the jugs you're jumping off the lower sprocket that can't be seen. Without constant upward pressure on the chain it will definitely fall off the lower sprocket and bind every time.

 

[Arclight88]

Hm, I don't see how the torque on the acorn nuts is going to have any effect on rotation if the cam is not even on yet. The chain should be completely free and independent of the jugs. The only thing connecting the jugs to the lower sprocket is the piston rings and the friction on the jugs created by them.

So, before the jugs are on it rotates freely, but once they're on it binds? It seems more likely to me, that when you're placing the chain through the jugs you're jumping off the lower sprocket that can't be seen. Without constant upward pressure on the chain it will definitely fall off the lower sprocket and bind every time.

Before the jugs are on - motor rotates freely.

With the jugs on - motor rotates freely.

With the head installed - motor turns (either way) 330 degree and no more.

During all rotation tests, I am holding upward pressure on the cam chain with one hand while spinning the crank with the other.

 

[bcware]

Ok, so the heads must be the problem. You said there is no cam on or cover causing valves to move at this point. The acorn nuts aren't going to make any difference because the difference in height from loose to fully torqued is not significant in terms of clearance unless the head gasket crush rings are totally flattened. The only option is that something is hitting your piston at or near TDC on one side.

Can you read the marks and tell at which point contact is occurring? RF/RT or LF/LT, etc? Can you get a nice clear photo of your head gasket and the valves seated in the heads?

Are your heads on backwards? I have to ask

 

[Arclight88]

Ok, so the heads must be the problem. You said there is no cam on or cover causing valves to move at this point. The acorn nuts aren't going to make any difference because the difference in height from loose to fully torqued is not significant in terms of clearance unless the head gasket crush rings are totally flattened. The only option is that something is hitting your piston at or near TDC on one side.

Can you read the marks and tell at which point contact is occurring? RF/RT or LF/LT, etc? Can you get a nice clear photo of your head gasket and the valves seated in the heads?

Are your heads on backwards? I have to ask

Why BC I am shocked, shocked I tell you, that you think that you need to even ask that question. Of course the head is not on backwards. But the right cylinder valves are installed backwards!!! I would have included a nice clear photo of the head with the valves installed the wrong way round, but it's just too much of an embarassment.



Sigh.

Oh well, the sun is shining, the birds are singing, and everything is going so well...

I'll see if I can actually follow the remainder of the written directions and avoid anymore FNG mistakes on this rebuild.

 

[drewpy]

good call BC

never would have guessed that one!

To quote Sherlock Holmes;

How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?

 

[Greasey Fingers]

mental note for my topend rebuild: check valves arent on the wrong way

Phew, this was spiralling downwards for a little while there. Good to see you have it sorted now, i like a story with a happy ending