Compression Question... Professional help needed!

[Tor-King]

So, I am in the process of rebuilding the engine on my '86.  It has only 32,000 km.  I recently acquired it from a friend of mine who had it in storage since 2003.  The year prior, it was stolen and then recovered.  It never ran well after that.  He said that they had done a compression test and that all cylinders were low.  He decided to park it.

Fast forward to 2016.  I did a compression test (cold with carburetors removed) and got these recordings (85, 72, 91 and 90).  I then added oil to each cylinder and the results were 140, 140, 150 and 148, still a little low according to specs.  Before I proceeded with a tear down, I checked all valve clearances.  They were all on the tight side but within specs.  Once I removed the head, I found that all bores looked very good with no visible score marks (all cross hatches were present). I also did a valve leak test and all was good.

I need some expert advice as to what could be causing such low compression results?  What is my next step? I have yet to check pistons and rings... BUT...shouldn't the pistons and rings be good seeing that the cylinder bores appear unworn and unscathed?

Thanks!
Dean   

[FJmonkey]

Adding oil helps seal the rings. Getting higher compression with the oil tells you that you are loosing some of your compression past the rings. Is the compression bad enough to justify the cost of pulling the jugs? I will let others toss in their opinion?

[Troyskie]

Could be frozen rings. As your effie has been parked up for so long they might need a free-up.
Yamaha make a fuel additive for it.
One of the Aussie members (Oldktmdude) Pete, discovered it on another members bike (Alf).
I believe I have the same issue on my 1100, probably the oil rings not compression.
I've just gone down the path of new rings, pistons, valves, re-bore etc on the 1200.
If it was me, I'd be ignoring the low compression and focus on the carbies.

[ribbert]

At that mileage, short of some catastrophic event, you would expect the cylinders to be in good condition.

For many reasons, I would take no notice of compression readings on a cold engine that hasn't run for 13 years, nor would I take any action based on the findings of a previous owner.

I specialise in pre-war vehicles these days and some of the engines brought to me haven't run for half a century or more. Unless there is some obvious mechanical failure, like a con rod hanging out the side of the block, the procedure is the same, get it running first. It's a lot easier determining it's condition as a complete engine and once it's been brought up to temp, run for a while and everything is re seated and clean off.

When firing up a perfectly healthy engine that has been parked up for a long time it is not unusual for the first minute or two to have missing cylinders, smoke and rough running, all of which resolves itself very quickly.

Continuing to dismantle for further visual inspection isn't going to tell you much and just add to expense. I would put the head back on, get it started, ride it a bit, then set about checking its vitals.

The original cause of "never ran well after it was stolen" could have been anything.

Noel

[CutterBill]

What Noel said...  

Personally, I find a compression test to be of little value; there are just too many variables to place any real meaning to the numbers.  A leak-down test is far more informative...
Bill

[jscgdunn]

My input would be to clean up the carbs well, sync the carbs ad get it running.  I would expect you will find it has ample power.  With only 32K it is barely broken in.

Jeff

[red]

Tor-King,

Yamaha Ring-Free may be found at dealers and on Amazon.

https://www.amazon.com/Yamaha-Yamalube-Ring-Additive-ACC-RNGFR-PL-12/dp/B002GU4SN2/ref=sr_1_2?s=automotive&ie=UTF8&qid=1472737868&sr=1-2&keywords=yamaha+ring+free

Cheers,
Red

[Tor-King]

Hi everyone!  Thanks for everyone's responses!

I may have to give a little more information that I did not post in my original.  The previous owner, once he got his bike back attempted to run it immediately.  He told me that the tank emitted a horrible odour and thought that the guys who stole it attempted to sabotage it prior to returning it.  He also thought it was abused as there was obvious evidence that they did burn outs...

He cleaned the carbs and even bought another set in an attempt to get it running.  It never ran well, and was extremely rough running.  At that point, BEFORE putting it in long term storage, a compression check was completed finding low readings.

I am in in this deep now.  I have the engine out of the bike as I am going over and replacing, replenishing, repairing every piece.

I got the bike earlier this year.  When I got the bike, it was sitting in a heated shop along with literally hundreds of new and duplicate parts to fix up the bike (with the exception of engine parts). The PO scoured the internet for years for replacement parts. He just never got around to completing it.  He pretty much gave it to me knowing that I would care for and complete the project (as I bought his other FJ 4 years prior).  Two months later, he passed from a terminal illness.  I want to fulfill his wishes.

Thanks again,
Dean

[Tor-King]

Update: I just removed the "jugs".  What a beatch that was with the lovely rubber/plastic coating on the studs binding up as I was lifting it off.  The rings on all pistons were free and not binding.  The pistons look to be in good shape.  I am sending a couple of pictures showing the bores and a couple of shots of the pistons.  What do you guys think condition wise? Hopefully the pictures are clear enough to show definition.  All the pistons look pretty much like the ones in the pictures.
Thanks,
Dean

[racerrad8]

The only way to really "look" at the cylinders is with a micrometer.

You need to check wear, taper and out if round.

Randy - RPM

[Tor-King]

Thanks, Randy.
I will have the cylinders measured.  Should I measure the pistons as well or can they be visually inspected for wear?  Can you tell by the attached photos if they are good to go? 

Dean

[racerrad8]

They too need to be measured.

Randy - RPM