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Does anyone know how long it takes to change out a cam in a Briggs 17.5hp OHV? I'm pretty sure my compression release mechanism is broke. Have adjusted the valves like 3 times, (4 & 6), but it won't turn over passed the compression stroke.

I have a blown 17.5 that I could rob the part from. But not sure if that's a good idea either. Considering the $80 for a new one.

1-2 hours depending how hard that sump gasket is to remove.

ILENGINE said:

1-2 hours depending how hard that sump gasket is to remove.

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Thanks. That's not too long. It'll probably take me twice that long. Considering I never get any deeper inside an engine that adjusting valves or changing push rods. But, this is a good mower. And I can sell it quick, when I get this fixed.

I go 5 and 5 on all my briggs that have overhead valves never had one come back for the same thing.....

Boudreaux In Eunice La. said:

I go 5 and 5 on all my briggs that have overhead valves never had one come back for the same thing.....

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That's were I started. 5&5, 4 & 6, 5 &7. And it won't go passed the compression. New battery. Good started. Etc etc.

How are you setting your valves if you can not go past compression? Just wondering.

BlazNT said:

How are you setting your valves if you can not go past compression? Just wondering.

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A couple of different ways. Either with both valves closed at the same time. Or sometimes I'll adjust them when just one is fully closed. I think I did it both ways with this one. Thinking I might not have gotten the TDC right.

When I do them with one open and one closed (adjusting the closed one), I'll turn the crank until the piston starts down, about 1/4". with out the valve moving. I've heard that's the most accurate.

The most accurate position to set valve clearance is when the lifter (or valve stem, for flathead engines) is directly opposite the peak of the cam lobe. It's easy to find this position without removing spark plugs, finding TDC, etc.

For the exhaust valve, that position can be found by rotating the engine in its normal direction until the intake valve just finishes closing. At the crank position where the intake valve has just finished closing, set the clearance on the exhaust valve.

For the intake valve, that position can be found by rotation the engine in its normal direction until the exhaust valve just starts to open. At the crank position where the exhaust valve is starting to open, set the clearance on the intake valve.

Do not mistake a slight opening of the exhaust valve as the actual opening of the exhaust valve. That is the compression release on some engines.

I can send you detailed instructions on how to set the valves which includes a way to check the compression release and a Service Manual IF you like. Unless you are a wizard of some sort, do the work the way the people who engineered and built the engine say to do it and that includes clearances.

Address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

Tinkerer200 said:

I can send you detailed instructions on how to set the valves which includes a way to check the compression release and a Service Manual IF you like. Unless you are a wizard of some sort, do the work the way the people who engineered and built the engine say to do it and that includes clearances.

Address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com

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Thanks man. Sounds great.

Watch & listen.
If the compression release is working properly you can hear the compressed air hissing out when you turn the engine by hand.
Also check the height of the valves when closed, they should be the same.
If the head got too hot and the valve guides moved in the head you can have the situation where a valve spring ( usually exhaust ) becomes coil bound and that makes the engine very very hard to turn over cold.
You should have 0.010" to 0.020" between the turns of wire on the springs when the valve fully open.
IF not the guide has shifted.
This will bend pushrods and cause excessive cam wear.

bertsmobile1 said:

Watch & listen.
If the compression release is working properly you can hear the compressed air hissing out when you turn the engine by hand.
Also check the height of the valves when closed, they should be the same.
If the head got too hot and the valve guides moved in the head you can have the situation where a valve spring ( usually exhaust ) becomes coil bound and that makes the engine very very hard to turn over cold.
You should have 0.010" to 0.020" between the turns of wire on the springs when the valve fully open.
IF not the guide has shifted.
This will bend pushrods and cause excessive cam wear.

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I haven't checked the push rods to see if one is bent. Such an easy check. I guess it just didn't cross my mind.

How can a valve guide that has moved out of position change the amount a valve spring is compressed?

I don't see how that is possible.

cpurvis said:

How can a valve guide that has moved out of position change the amount a valve spring is compressed?

I don't see how that is possible.

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When the heads overheat on small engines, the guides move up inside the springs and will hit a point that will prevent the valve from fully opening because the valve retainer hits the guide., causing broken or bent push rods.

ILENGINE said:

When the heads overheat on small engines, the guides move up inside the springs and will hit a point that will prevent the valve from fully opening because the valve retainer hits the guide., causing broken or bent push rods.

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Yes, I understand how that could happen. It can lessen the amount of spring compression, but not increase it. Coil binding is increased spring compression.

When the head gets hot the valve springs pull the valve guide up out of the head.
When the guides get nice and loose the rocker pushes the valve stem down and the guide goes with it .
The valve looses heat through the seat & the guide.
If the guide is not a tight fit in the head the amount of heat the stem looses decreases and the valve sticks in the guide and the guide moves in the head
Engines tend to stop with the inlet compressed or partially compresses so the guide then ends up being too low and when rotated cold the coil binds.
Usually the inlet ends up in and the exhaust ends up out

I understand the part about valve guides moving. I also understand how the valve spring retainer can hit the guide if the guide moves too far out of the head.

But no matter which way the valve guide moves, it can't cause the valve spring to be compressed too much, aka 'coil binding.' It's just a sleeve that is a slip fit on the valve stem and a press fit into the head. The cam lobe lift and rocker arm ratio are the only two things that determine how much a valve spring is compressed.

Unless I've overlooked something big, that is.

hrdman2luv said:

Thanks man. Sounds great.

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That only works if you contact me at address posted.

Walt Conner