Low Compression

Hello all thought some of you guys might be able to help me out. I have a 1992 VFR Just picked it up a few weeks ago and I was told by the PO there was an intermittent power loss. I think the repairs were above his head because things he told me he checked the most obvious ones were not. I got a great deal on the bike but it was half apart and not running. I was able to get it started and found a few carb diaphragms were torn so I replaced those pulled the carbs apart they were in great shape. They had put new plugs in it and a bunch of new fluids. Well come to find out it has a dead hole on #3 cylinder. The coil is good plug is good wiring is perfect. I however have only 60 psi on that cylinder. #1 has 90, #2 85, and #4 110. So my question is as this is my first Honda was there any issues with these motors? I am kind of at a loss the bike only has 26k on it and I have been a mechanic for the last 16 years I know everything Honda has built has been bullet proof engine wise. Just trying to maybe get some Ideas before I pull this motor apart to rebuild it. Thanks in advance.

 

the short answer is no. 60 psi sounds like a broken ring or a valve not seating properly.

 

My thoughts as well. Guess its time to get this thing stripped down. Any ideas where would be a good place to order a rebuild kit from? Might have to hire someone to do this one. Thanks TNRabbit

 

Whoa, there, Bunky ! Compression should be tested with engine at operating temp and with throttle held wide open, right ?? With and without 1/4 oz oil in cylinders too.

Not wise to tear things apart until you've located sources for whatever parts you'll need.

 

Squirrelman yes I did exactly that. I was able to source out some of the parts before I even attempted the rebuild. I tried everything I know in my bag of tricks to make sure this was the issue. I just hate knowing that with this low of miles this has happened. Luckily all the engine rebuild parts are available with some looking around.

 

You did the oil test to determine if rings or valves are at fault ??

Learned my lesson long ago, and i'll never buy a bike without making a simple compression test first !

 

Yea I did the oil test and was able to verify that the rings were bad. The valves all look great so I have at least that going for me. Pulled the rear head off of it a little bit ago to just to see how things looked.

 

Well after a lot of work finally got the 750 running. After pulling the rear head off I found that the intake valves had a ton of excess carbon on them. After talking to a few people found this was common when someone uses the improper fuel and does not keep the carbs tuned right. After some careful diagnosis found that when coming up on compression stroke the cylinder pressure would escape through the intake valves on all 4 cylinders causing my lack of compression and a dead #3 cylinder. So I decided to rip the motor out pull it apart and replace the pistons and rings while I had the heads off. Did that repaired all the valves in both heads put the motor back in and it started right up and now runs on all 4 cylinders. Totally worth the tear down now knowing this motor is in great shape.

 

A little seafoam and some time putting the bike through its paces could have saved the tear down. But either way good to hear you got her fixed and purring again.

 

Zen yea I heard the same thing but the PO tried it and I guess maybe he did not do something right but will defiantly keep that in mind for next time. Thanks man!

 

Just curious about your source for pistons and rings ??

 

I actually found them on EBAY they came off a motor with only 2k on it. I could not pass it up they were in perfect condition. He is a pic of them installed.

 

Nice work ! Man, you sure don't waste time ! I'm surprised they'd break apart a 2k miles motor rather than sell it whole.

 

Squirrelman i was thinking the same thing. I want to ride so bad and I left the us for a couple weeks so had to get it done. Ready to get back next week and put the rest of it back together.