1931 Model 42 Mosquito Sprayer

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    Hi, guys,

    Remember our drive to Williamstown when we used 3 1/2 gallons of oil in the 850 miles? Well I finally got some time to pull the head and have a look. From the looks of the head there’s baked on carbon in several cylinders. It’s number 4 that’s been throwing the oil. I’ve attached photos of the head and the cylinders. It really looks like it just needs decarbonizing. I’ll clean it up when I get back from the Gathering at Gilmore and see if there is any trouble underneath all the carbon.



    Second photo


    Third photo


    Show us a photo of #4 piston at the top of the cylinder. Is the piston clean around the outer perimeter? if so, the rings are bad or stuck in the grooves, the oil is washing the top of the piston clean. Since you have the head off, I’d drop the pan and push at least that one piston up and out, and inspect the rings..

    Greg L


    Here’s number 4 and I’ll post number 5 in the next one


    Here’s number 5.


    Looking at the photos, I’d say the rings are stuck in their grooves or worn out on these two cylinders.. especially since you fouled #4 spark plug with oil if I remember correctly.

    Time to drop the pan, and order some rings..



    Can you get rings for pistons made in the 50’s? That’s the last time it was rebuilt. I’m thinking that I’ll wait until I decide to do the whole engine.



    The rings are available. You can order them from most any piston company.


    Bill: is there a significant ring ridge on the cylinders? Usually, if the rings are badly worn, the cylinder bore will have a lot of wear as well, from the dirt that caused the ring wear.

    This may not hold true with Pierce’s very hard cast iron.

    But if there is no significant ring ridge, I’d pull the piston, and look for stuck rings.. you might be lucky and find the oil ring stuck in it’s groove, and be able to free it up, allowing it to reseat and control the oil currently being pumped up past the rings into the combustion chamber.

    You’ve spent the money and time on the head gasket and labor, I’d go ahead with dropping the pan, and attending to the oil consumption.. it might be fairly easy.

    Greg L


    This is a very informative discussion.-thanks all. Bill, just curious, did this car have solid oil pressure when hot, at idle? If so, it would be interesting to see the outcome of a cheaper surgical fix like rings as Greg suggests and perhaps a valve job as long as the heads off, in lieu of a complete tear down.

    please update us on your findings and decided path-sharing this is much appreciated.



    Hi, John,

    Oil pressure is great on this engine. Hot idle pressure is about 15 lbs. I’ll make more decisions after everything is cleaned up.



    Here’s the exhaust valve from #4. There is an area that has enough deposit on it to raise the valve. Measured clearance was .013 and it was originally set at .008 cold. This deposit scraped off and I’m sure that I’ll be able to lap the valve in without any problem. These are all original valves, so I don’t want to have them ground if I can avoid it. While the valve is not burnt,I could hear the starter skip a beat when cranking the engine and that told me to check compression. Cranking pressure on this cylinder was 30 lbs. The others ran from 60 to 80.

    The head is now fully cleaned and I’ll work on the block this weekend. If all goes well, it will be back together on Monday.



    Bill, thanks for adding this info on the exhaust valve. This a sequence I propose happened with your engine for your consideration:

    a)The rings on cylinder 4/5 slowly degenerated or perhaps didn’t seat properly when placed in service with the last ring work, eventually allowing significant amounts of oil into the combustion chamber 4/5, and of course, giving lots of blue smoke.

    b)The oil in the combustion caked on the exhaust valve in 4 to the point the valve was lifted, giving poor compression, thus poor combustion, allowing oil in its liquid state to foul the plug. I bet 5 was heading the same way.

    So, if the exhaust valves are cleaned/reseated and the engine placed into service , combustion will be restored, performance will improve and rpm’s will increase (for a while) but the car will eventually return to b) in the sequence above. I believe the rings are the root of your troubles as Greg L has indicated and perhaps that is part of the block work you indicate for the next few days.

    I wish you the best on the weekend project!

    John W.


    Well, it took a week longer than I expected, but it’s all back together. I wound up having the exhaust valves dressed. They had little pits in the sealing surfaces that would not lap out. Now they are fine and the seats cleaned up with lapping. The intakes showed no wear at all and 6 out of eight had exactly the same clearance .006 from the last time I had the head off 15,000 miles ago.

    As John predicted, I need to set my idle a little lower as it’s running better than it has for a couple of years.

    I really do plan to tear this engine down in the future. But I can now feel good about waiting a couple years for that.



    Thanks for the update Bill. Sounds like your cars is all set!

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