B&S intek engines not starting and stopping turning over on the compression stroke

[keakar]

i have an intek 31C707 17.5hp and an intek 331877 19hp with the same issues

both spin over easy and free with no spark plug so i set the valves, which were a little off on both engines but not by much.

i confirmed flywheel keys for correct timing on both engines and they both spin free until the compression stroke and then the starter cant turn it any more and they both have good spark and i even disconnected the gas line in case they were flooding or hydro locking but they arent and even with no gas that didnt help them be able to turn over at all.

its not locked up or stuck, it just has a lot of compression stopping the engine from turning over.

i even connected to my truck battery to eliminate any weak battery issues and nothing changed

i have never run into this before, all the times before i just set the valves and walla engine spins easy and starts right up, so im at a loss whats going on here.

both engines are from unknown history but visibly look nice and not like they were sitting out side unprotected.

i opened one up and there is no evidence of anything being bent like a piston rod or any cam issues that i could tell just by looking at it.

anybody run into anything like this before and have some wisdom they can pass along to me?

 

[tom3]

Kind of points to the compression release mech. on the camshaft broke or stuck? One thing we used to do with the old Gravely tractors is to manually turn the motor over to the compression stroke, then on into the compression some. Then hit the starter and the increased speed and flywheel inertia would let it turn over till it started.

 

[bertsmobile1]

Inteks have an ACR on the inlet cam
As Tom mentioned , if it is not working properly then stater can not turn the engine past TDC on the compression stroke .
However even if the ACR is fine on the cam, if the valve lash is too big then the very small opening of the inlet will not happen so the engine will not decompress .

 

[keakar]

thanks guys, so your both suggesting it could be the compression relief on the cam?

i assume its not a separate part or is it?

 

[bertsmobile1]

The little dohickie on the bottom of the camshaft is the ACR mechanism
THe spring goes then it falls apart
At rest it should snap back when moved out
You will see a little pin that makes a bump in the inlet cam to decompress till the weight flings out.
They are not particularly robust & I replace 1 or 2 camshafts each season
cam shaft

 

[keakar]

thanks, while im in no way a novice mechanic, this is the first time i started digging into the inside of these engines because, well quit frankly it was easier and in most cases cheaper to buy a parts mower with running engine rather then fix one with issues. i feel a little ashamed i never bothered to learn that much about them other then the list of things to do when they wont run. in the past, when i got to the point nothing worked after i was sure i had good timing, good spark, gas and good compression, and valves were adjusted correctly, i just scrapped it and moved on to the next engine.

 

[bertsmobile1]

Nothing to be ashamed about.
All of the people who got a good used part t get their engines running would have been most thankful that you parted out the engines.
If it helps. I have 4 cu meters of engines that could be fixed sitting in an old van waiting for me to get around to fixing them.
And the pile gets bigger every season.

 

[keakar]

I have 4 cu meters of engines that could be fixed sitting in an old van waiting for me to get around to fixing them.
And the pile gets bigger every season.

and thats exactly why i gave them to the scrap metal guy. at one point i had a dozen engines and about 15 trannys and one day i finally admitted to myself im never messing with any of that and no one wanted those trannys and i may have had the need to use only one of them in 3 years. i did use a flywheel or two and the cooling fans and covers came in handy, seems people lose everything when they trying to figure out why a mower wont run before they sell it. one guy had no idea where the cover or the carb and intake were at lol.

i used to buy parts mowers and try to sort them to may one good one out of 2 and once even 3 when a really pretty one needed a deck and an engine so those had to come from 2 other mowers

i gave that up because the out of work mexicans in my area were buying junk mowers for nothing, then spraying carb cleaner in them just sop they start, and then selling them for $250 so there was no sense even trying any more if they sell for less then i spend on them. i like to fix everything, everything, including tune up and sharpen or replace the blades so...... i dont begrudge them hustling to make money but dont rip people off and dont undercut prices so guys doing it for a living cant make money any more.

lots of guys i sold mowers to had bought one of those mexican "great deal" mowers and they all said to me that they had to fix everything on it after they bought it and it still wasnt working right so they bought one of my mowers

 

[keakar]

Nothing to be ashamed about.

ok well then teach me some more please

what about the twin cylinder engines? do they also have a compression relief on the cam or do they have something different?