I've been doing more sailing than riding this past year but I couldn't resist buying an '87 Concours with only 16,000 miles on the clock last week.  Looks to have been garage-kept her entire life.  Found her, literally in a barn on Whidbey Island.  Extremely clean. 

The problem is low compression across all four cylinders.  I've replaced C10 engines before so that's not a problem. I bought a used one last week to go with this bike for parts or an engine swap.  The replacement engine has 30,000 miles on it but is untested. 

The previous owner said he lined the gas tank with POR-15 and that looks good.  The PO also rebuilt the carbs and they have fresh carb boots...probably the most exciting part on the bike for me ha.

The PO also said the bike sat for two years and the engine seized.  He said he freed it up with Seafoam in the cylinders but now the compression is too low.  So he assumes that the cylinder walls and rings are damaged enough not to build compression.  My spare engine should cover the parts I need for this repair. 

Questions:
Can the Cylinders and Pistons be swapped into the existing engine with the engine still in the frame?  I'd like to not have to remove the swingarm to swap entire engines because the bike's sitting outside. I don't have an indoor shop for the work but at least the weather's good here in Seattle. 

Is it worth swapping cylinders and pistons or would it be a better option to swap in the complete 30K engine?  I like the quality of the maintenance I'm seeing on this bike and trust its bottom end.  The 30K engine might have unknown problems.

Before swapping either the engine or the cylinders-and-pistons, I'd better do some more checking of the valve train.  I can check valve clearance but could probably use some guidance on the cam chain position check.

I also scrubbed the forums and found references to a guide pin/dowel that can accidentally shear off when hand-turning the engine with the 15/16" nut on the timing rotor.  How can I inspect that pin and verify the valve timing?

Also, the compression numbers were all around 125#.  I lost the exact measurements but they all measured between 120-135#.

Was the engine warmed up when the compression was checked?

You'll usually get higher compression when the engine is warm from running.  Although your numbers are low I believe by the book they are still within speck.  I would try adjusting the valves and riding the bike for a while to see if the compression comes up any, you might just have some stuck rings that could work them selves out with some ridding.

And, yes, the top end and pistons can be removed without removing the rest of the engine from the bike.

Wow, lots of variables here,
First off, does it run?
Now, obtain a factory service manual, you will need it...

When doing a compression check, you need to use the type of tool that screws into and seals in the spakplug hole, not a hand held one with a rubber tip.
You also need to hold the throttle wide open during the compression check.. if numbers are low, pour a tablespoon of thin oil, or kerosesne, in each cylinder, spin the engine, and recheck compressions.

As for turning the engine over by hand, with the stator nut, if all the plugs are out it is no problem.... don't try it with the plugs installed tho.

Check first thing, to see if it was hydrolocked, and has bent rods, see the sticky thread above this, for the method... determine if this was actually wy it was seized up...
As for swapping parts from a different engine, yeah, you can do top end, but if you need to do rods also, not so much, as differences in crankshaft bearings may necessistate engine removal and determination as to if a Swap can be made.

If the top end was never disassembled, there is no need to mess with the timing and cam chain, simply verify correct valve adjustments.
Sitting as long as it has, dump all the fuel, and clean the gastank, even tho it was coated prior, remove all the old fuel...if the p/o did the por15 treatment, no telling how long he let it dry before fueling it, and that causes issues with carbs also.
Like I say, lots of stuff to accomplish beforehand...

Thanks guys. I'll check these items off as I go.  I also have a Kawasaki factory service manual and some teardown-buildup experience with the zg1000. I did a 1052 build a couple of years ago and know what it takes to split cases to change the rods. I don't want to split the cases on this project and would rather use the spare 30K engine than do that. 

Tank is dry, carbs were rebuilt by the PO and there's a new petcock so the fuel system seems to check out ok. I'll hook up the tank and put some fuel in it, see if it starts, check compression, reverify the carbs after I pull them, check for bent rods, verify the timing and inspect the timing plate pin under the stator nut to see if it's sheared off.

Thanks for confirming I can pull the cylinders and pistons with the engine in the bike.

IIRC, If after checking the other stuff (no bent rods) and the end result is swapping parts to raise the compression, you should be able to just swap the cylinders and related pistons without spliting the cases. Just remove the head, slide the cylinders off of the pistons, then remove each piston from the rods by removing a retaining clip and sliding out the piston pin. Keep everything in order in relation to the cylinder it came out of and reverse to install.

After all that work, you may see no improvement...
If you go to the trouble of pulling of tyhe head and cylinders, simply hone the cylinders to hatch them and break the glaze, and install new rings, properly sized and gapped... and reassemble.

Simple, and you don't have to geuss if the rods and pistons are weight matched.

IIRC, If after checking the other stuff (no bent rods) and the end result is swapping parts to raise the compression, you should be able to just swap the cylinders and related pistons without spliting the cases. Just remove the head, slide the cylinders off of the pistons, then remove each piston from the rods by removing a retaining clip and sliding out the piston pin. Keep everything in order in relation to the cylinder it came out of and reverse to install.

Thanks for confirming the heads and pistons are an easy swap. I suck at ring gapping or I'd probably take MOB's advice.  Heck, if I hadn't already bought the spare engine, it might have even been a better idea just to re-ring this engine.

Truth be told, I'm really hoping that the timing rotor shear pin was sheared off when the PO was rotating the crank by hand to free up the stuck pistons.  This seems to be the most likely cause of uniformly low compression.  If the pistons were exactly and specifically rusted across all cylinders, then a uniform compression loss could have happened though.  Maybe even a bad valve/adjustment -- but all of them?  This whole paragraph is rhetorical and speculative. None if it means anything until I start inspecting and verifying the condition of things.

Thanks for the input and feedback.

 

personally I'd rather check and file ring gaps and install, than change out a set of tires in my garage...

I don't sweat and knock teeth out doing rings...

but to each his or her own, just reiterating that when you swap things as you are planning, you should at least check the ring gaps, as you have it all apart, you may find as I also noted, little improvement if there was wear issues on the donor parts.

be safe, and best of luck on the venture,

MOB's advise is really the ideal path to take. I was just pointing out that the process was possible, but, by no means real easy. Trying to get each pair of piston's rings compressed and in the cylinder, then turning the crank enough to do it with the other two pistons.... while trying not to pull the first two out too far.... yeah, it's a bit of a bear. BTW, a sheared pin at the timing rotor will not make the engine mechanically low on compression. It will change the ignition timing which can make the engine run like its got low compression if the timing is retarded enough.