5hp hayterette compression issues

[disco2]

Hi all hope everyone is keeping well. I picked up a nice 5hp hayterette a while ago it’s in pretty good condition but it seems under powered. It’s starts up fairly easily but it tends to bog down and stall much easier than I would have expected. When it tries to stall it can usually be recovered by putting the choke on . I cleaned the carb out and replaced the diaphragm and gaskets in the carb. It’s a pulse jet carb. I did a compression test and I’m only getting around 45 psi. If I add some oil into the cylinder I’m getting about 60psi which is way down still. Valve clearance is about 2 thou on the inlet and 5 thou on the exhaust valve. Before I go opening it up I wanted to check these engines don’t have a automatic decompressor. It’s a 5hp cast iron sleeve with stellite exhaust valve and ball bearing crank shaft. It says easy spin on the recoil starter. It’s does smell a little oily when you work it hard but no smoke on start up. I’m wondering if it has either worn rings or even broken a ring. Any way any thoughts would be much appreciated.
Best wishes William.

[sidevalve5]

Hi William,

Am presuming the mower has a Briggs & Stratton engine. If so, I have found they sometimes need fine tuning with the mixture screw to run well. Have a 12HP model on a Ransomes Bobcat mower and even 1/8th of a turn on the screw can make a big difference. Do not think a normal compression tester is the best tool to use on hand start single cylinder petrol engines. They really operate best when the engine is running at least electric starter speed. The correct tester is a leak down type. But if you do not have access to one and I do not. I use the thin latex glove method. Fit the glove tightly over the exhaust and bring the engine onto compression. If it rapidly inflates, its the exhaust valve leaking. Do the same test over the carb inlet and if possible over the oil filler hole. This will test for blowing past the rings. The glove will inflate a bit, but if it rapidly does so, it identifies the problem area. You valve clearances seem a bit small to me. Would check the manufacturer’s recommendations.

Best wishes,

Grahame

[disco2]

Hi Grahame thanks for your reply,yes it is a Briggs & Stratton engine that was the bit I should have mentioned. I will give the gloves idea a go. I will also have a play with the fuel mix adjustment as well. I found the valve clearance and it should be between 2 and 5 thou on the inlet and 5 and 7 on the exhaust. I contacted a Briggs & Stratton agent today and a set of rings if available are almost £60 pus another £45 for the gasket set. The fact that it’s so starts 2nd or 3rd pull from cold and it’s overall condition I would not expect it to need such major surgery like piston rings etc.
I will let you know what I find.
Best wishes William

[davidbliss]

Those little Briggs have that odd way of a compression release by a bump on the back of the inlet cam thats a horrible idea, thats why the odd valve clearance 2-5, so you must not get the cam in the wrong place when going to adjust. I once just ground that bump off, this made the engine run like any normal engine, however it could snatch a bit on the pull-start but it went years after that.

[disco2]

Hi David thanks for your help so those engines do have an automatic decompressor on them so hopefully that explains the low compression reading I will have a look at it again over the weekend and try the glove ideas suggested by Grahame.
Thanks again for your help.
Best wishes William

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