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AQ151C Compression Readings?

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Paul McClure

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I'm still getting fuel in oil and want to compression test the engine to verify the condition of the piston rings. What readings should I be getting?<br><br>As an aside, I'm really getting close to replacing this engine. Another season wasted, I've just about had enough...
 
Fuel in the motor:Could be the needle seat or the float is set wrong.Could be the mechanical fuel pump has a pinhole in the diaphram.
The compression should be even on all 4cyl.Different guages give different results.I imagine anything above 130# is acceptable.J
 
Just had it tested:

Cyl 1 - 175 psi
Cyl 2 - 163 psi
Cyl 3 - 180 psi
Cyl 4 - 188 psi

So a bit of variation, but good enough readings to discount worn rings?
 
Your main differential is between #2 and #4.
If this is less than 10%, most will say that this is acceptible.

Your fuel in the oil may be the fuel pump, as mentioned.
While I'm not one to recommend throwing parts at an issue (without first varfying), a fuel pump replacement is not a bad idea.
 
I just went through the same thing two weeks ago and it was the carbs. Does the engine run okay? No black smoke? No flooding? Do the plugs come out wet?

It's important not to run the engine if you are getting excessive fuel as it washes the lubrication from the cylinder walls and you could end up with a smoker. I'm thinkin' it's a stuck needle or the float has sunk.


 
Hi Mike, yep, I suspect the carb as well. It was definitely flooding, fuel in oil, black/wet plugs etc. I put this carb on the boat just before it blew out a big end bearing. With hindsight, I think it was over fuelling back then and diluted the oil, causing the initial failure. I just wanted to compression test the engine and verify it is good before sending the carb back to get it checked out. I'll send it back tomorrow, hopefully the guys at the shop can check it out and resolve.
 
Paul,

I'm not certain what carb that you have for sure, but I have twin carbs on my Volvo and rebuilt both from kits that I bought on-line and it wasn't a bad job.

The compression may well stabilize somewhat after you get oil back on the cylinder walls.

I think you are correct about the bearing issue. I caught mine before any internal damage. Mike
 
Mike, I swapped out the twin Solexes for a Weber 38 DGES (electric choke) and new intake manifold after reading some positive posts on this forum. The reason for the swap was poor running with the Solexes even after the carbs had been rebuilt, that was later (after the Weber purchase) traced to a missed vacuum leak. Of course with no choke on the Solexes, the Weber is a good upgrade for cold starting.

However it looks like there's been an issue with the carb (which I'm sure is rare - everyone else seems to have had a good experience with the modification) which has resulted in over fuelling. After the bearing went I had the engine rebuilt with the crankshaft reground and new bearings, oil pump, full gasket set and valve stem oil seals etc. The cylinders weren't rebored as they had no visible markings and the piston rings were a good fit.

To date I've swapped out lots of parts:

Ignition leads
Plugs
Fuel pump
Ignition Coil

The fuel in oil issue has been really frustrating - the boat has been in the water since the beginning of June and hasn't managed to move away from the pontoon - and I was actually going to go back to the Solexes - except I seem to have misplaced the fuel line that runs between the two carbs. I have all the linkages and manifold, but am missing that one bit. But since we seem to have verified that all is healthy in the block, I'm going to give the Weber one last chance. If I still have problems after that, then I'll source a replacement fuel line and revert back to the Solexes, or even re-engine the boat, worse case. Given the engine itself is OK then I may just sell it as a good base engine on eBay.
 
When I was having trouble, the single carb idea was run by me, but about $90.00 in kits made the original twin Solex arrangement purr like a kitten.

You may well have had a high float or a bad needle seat from the get-go. I'm bettin' that when you get that thing right you will be well pleased with the outcome. I do understand the frustration, but better days are coming. Let me know when the carb fix is in.

Mike
 
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