# Honda GX160 ... only 50 Lbs compression



## Fix

Initially, when trying to start... one hears a slight "pop" sound now 'n again. When it DOES finally start........... it barely idles........for awhile, then dies.
A Leakdown test shows there is NO leak.......... or next to None. A standard, regular compression test shows only 50psi, when there should be a minimum of 85. Valve clearance is correct.

It's got me baffled, ................. I have one idea, but I'd like to hear from you experts, please??


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## MrChooks

:wave: Hi & welcome to TSF - 

Does your engine have a decompression arrangement to allow easy starting?? These things are sometimes marketed as "easy start" or some similar terminology.

I ask as assuming that the engine isn't just worn out hence low compression - then the low compression might be caused by a stuck decompression start unit :4-dontkno


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## Fix

It MAY have, but as I mentioned with the Leak-Down test (aka: Differential Compression test) it shows to have 95+% compression, turning CW or CCW. 

I'm thinking "Sticky" valve, and presuming it closes fine while performing the Leak-Down test, as it's sitting still with Air pressure closing it, but when performing a regular Compression test using the recoil starter, it Sticks, not closing properly. What do you think?


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## MrChooks

:wave: Yes - it certainly could be a sticky valve and as this engine is OHV - you might be able to see what is happening by taking the plug out and the rocker cover off and pulling the engine thru and watch the valve movement and have a look at the valve / tappet clearances.

Given as you said, that it passes a static leak down test, I guess that eliminates a burnt valve or seat.

This is a fairly easy / cheap test - so worth a look as a start. If the valves are all OK - then we will have to look deeper into the engine :sigh:


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## Fix

Thks MrChooks, ........... well I've poured some Rislone Karbout into the Spk Plug hole............. I'll let it sit for a day or more hopefully, & see if that does the trick. Whadya think?


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## MrChooks

Hi Fix - I am not familiar with Rislone Karbout - but I guess its worth a try as a 1st - at least you wont have to pull anything apart to try it:laugh:. 

My experience with "sticky" valves has nearly always had me physically freeing / cleaning the valve stem - as that is where the "crap" that fouls the free movement of the valve usually builds up.

Just a point - if you are lucky and the Risolene works - be sure that you change the oil before you put the engine to serious work again - as some will almost certainly leak into the crankcase and dilute / foul the oil.


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## Fix

Thks, yeah...... Karbout is a product we've used here in the Frozen North (Canada) for 30+ yrs........... removes carbon & gunk that builds up in the Upper Engine.............. sometimes works  Thanks for your help


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## MrChooks

OK - well given you are in for an oil change anyway - is the Rislone product OK / safe to pour into the crank case as well - 

Just a thought - but if it can clear gunk off valves - then it might also clear any muck that might be fouling the engine's decompression / easy start mechanism.

I've never done this - but if it is just a solvent - maybe you could drain the engine oil and sloosh a load of the stuff around in the crankcase / cam shaft area. You would have to make sure you got it all out afterwards and maybe do a double (1st oil change as a washout) oil change at the end.

Just a thought and as I said - I am not familiar with the product and have never tried this - but might be worth a try as my experience with these decompression / easy start mechanisms is that they are located down in the cam shaft area of the engine - so its a pretty big strip down to get to them.


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## 93-5.0

It could most certainly be a stuck valve because of sitting for a while but i work eith these hondas all day long and if any thing goes wrong with these things it is usually rings have been wore from tremendous amounts of use so i think it could be rings or a compression release


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## K-B

50lbs compression is not at all unusual for a 4 cycle engine...

Stuck valves can sometimes be freed with Marvel Mystery Oil. It's amazing stuff, we've even seen it free up seized engines.


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## Fix

93-5.0, you think the problem could be RINGS, even though the Static Compression Test (Leak-down) test shows 95% compression (Virtually No Leak)?


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## Fix

K-B, It will barely run with 50Lbs & Honda Spec's. are Minimum of 85 to 120psi. I'll check out the Marvel Mystery Oil, thanks.


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## MrChooks

:wave:I also have one of the l'ill Honda engines and have run it for years without any problems at all. I agree with 93-5.0 - that unless you engine has had an enormous amount of work (or run without oil) - then rings should be OK

See how these whiz bang additives work - but if your problem has come on quite quickly - I would doubt that it's worn rings - these things (worn rings & excluding catastrophic failure -which you would hear) generally just ware out over time - in other words a long slow degradation in performance and a noticeable increase in oil burn / blue smoke

If you engine was working fine - then all of a sudden you find you have low compression - then I would suspect stuck valve or decompression mechanism.

See how the Marvel Mystery oil etc works but if that fails - I think you are going to have to take the rocker cover off - check the valve movement / function then keep digging until you find "where the compression is going" :sigh:


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## K-B

The reason low compression is "normal" in 4 cycle engines is because of the automatic compression release, thus it is usually difficult to get an accurate compression reading.


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## k2skier

You would have to spin the engine over approx 1800 RPM's to get out of the comp release mode. A leakdown test by far the most accurate. I would look at the flywheel key for shearing and maybe try some starter fluid to see if it picks up RPM's, because fuel nowadays is the biggest problem with small engines.


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## K-B

k2skier said:


> You would have to spin the engine over approx 1800 RPM's to get out of the comp release mode. *A leakdown test by far the most accurate.* I would look at the flywheel key for shearing and maybe try some starter fluid to see if it picks up RPM's, because fuel nowadays is the biggest problem with small engines.


Absolutely.


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## Fix

Well, the Karb-out made no difference, so I ripped 'er apart. There's no gumming on the valves ('operate nice & smooth); decompression release works just fine......... no binding, nice 'n smooth. While I had it apart, I lapped the valves. Reassembled, & now, maybe another 5 Lbs to a total of 55 (as opposed to the Honda Specs of a Minimum of 85)........... & won't even fire. This engine hasn't many hours on it......... 'can still see the Cross-hatching in the Cylinder. Any OTHER suggestions folks????

Oh, & Pls. tell me K-B, why you think a sheared flywheel key would affect compression?


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## MrChooks

:wave: Fix - this is bizarre - given all you have done, I am running out of ideas - if you have the valves lapped, the decompression isn't stuck and the cylinder walls are good - yet you still can't get compression and the damned thing wont start.:4-dontkno

Look - here is something out of left field - and based on the fact that getting a good dynamic compression test with the decompression unit is difficult - based on the fact that if you have fuel, spark and compression - all engines just have to start - 

Have you checked that you have a good spark?? Don't throw rocks at me for this one - but I am wondering if due to the difficulty in getting an accurate dynamic compression test and your leak down tests seem OK - whether the compression issue is clouding the picture here.

Have you tried to pull the engine thru with the plug removed and look to see, if with the plug grounded, there is a reasonable spark on the plug. I only ask because my experience with these l'ill Honda engines is usually very good and am starting to wonder if we have all been looking in the wrong place:sigh:


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## MrChooks

Fix said:


> Oh, & Pls. tell me K-B, why you think a sheared flywheel key would affect compression?


I think K-B was referring to a possible timing / firing disruption rather than an effect on compression. If the flywheel key has failed and the flywheel moves out of its position - the spark still appears, *BUT at the wrong time *and the engine just wont start or run at all - even though it all turns over nicely and you still get a spark on the plug when you test it.

As I said in earlier post - I am running out of ideas:4-dontkno - so having a look at some of the more odd-ball fixes are worth a try.


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## Fix

Thanks MrChooks. Yes I did pull the plug & chk for spark, & as I know that on rare occasion a "sparking" plug will fail under compression.... I tried a new plug as well--- Great Spark! As you say, it IS Bizarre! 
I think the only other possibility is Weak valve springs? At the moment I'm waiting for a COMPLETE Service manual (as opposed to the free manual I was able to download off the net).......... MAYbe there will be some tips there, as well as specs on the springs.

(Oh, & I am well aquainted with the effect a sheared key will have on the timing..... I was just curious what K-B's reply would be regarding the compression,... thank you)


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## MrChooks

:wave: Fix - pls let me know how you get on with this - coz now it's driving me nuts too - I am sorry but I am just out of ideas on this one - short of suggesting your little Honda is cursed!!!


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## MrChooks

:wave: Fix - I have thought about it & decided that Honda engines can't be cursed (only vile old Villiers engines are cursed at manufacture!!:upset

So - lets start at the beginning - and no throwing rocks at me here pls :4-surrend - Did your problem with the engine starting come on quickly - or has it been developing over some time??

Have you tried tipping about a teaspoon full of good fuel down the plug hole and see if it will start at all - as even with only 50lbs - it probably should start - albeit and run poorly??. This is an easy test that you could try whilst waiting for the Honda manual to arrive.

If you can get your little monster to start at all - we may be able to close in on the underlying issue:sigh:


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## Fix

MrChooks,.......... thanks for Hangin in there! No rocks to throw,........ no feeling it's needed

The engine isn't mine,........ but a friend's. He says, it happened suddenly -- or within an hour or so,....... the way he describes it. 

I didn't try fuel in the plug hole, but Ether (starting fluid) in the intake, & to turn it over not by the rope, but I've a device I have which allows me to use a 1/2" Electric drill ------------------ didn't fire Once! Not a back-fire, ..... zip.......... nothing.
------------ Fix


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## MrChooks

:wave: Hi Fix - *AAAAAAAAAaaaaaaahhhhhhhhhh!!!*

This little Honda will have me sent to the loonie bin!!. I am completely at a loss now - so it wont even cough with starter fluid - with that stuff engines with almost no compression will respond if there is even a 1/2 respectable spark!!!!!

As you say the engine stopped functioning properly very quickly - it is unlikely to be rings or bore / piston issues -

Have a try (again with your ether - but put a small squirt straight down the plug hole) but using the recoil (rope) starter. Let me know if you feel any compression build up as you pull the engine thru.

If we can get this little bugger to start and run regardless of how roughly - we might be able to close in on its problem.

Fix - I got to say I admire your patience with this little bugger of an engine - coz if it were me - I think I would have converted the l'ill bugger into a boat anchor by now!!!! Anyways - we will persevere - no damned Honda is going to get the better of me!!!


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## Fix

Thanks for the compliment regarding my tenacity MrChooks, but I figure it's JUST a machine....... WE are the rulers! If it was built by man... & it ran once, it WILL run again......... I hope

I did that.... sprayed a Goodly amt. of ether in the plug hole(enough to normally blow the head gasket/bend push rods)....... didn't feel much compression build up pulling with the recoil.......... & the only reaction was one, maybe two barely audible "pops". 

----------- Bewildered Fix


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## MrChooks

Fix - I have renamed your engine - *"Hirohito's Revenge"[/*_I]:upset:

OK lets see if we can eliminate rings / bore damage issues. So remove the plug and using an oil can put a squirt or 2 of engine oil (the heavier the better - but your normal engine oil will be OK) down the plug hole and pull the engine thru for a couple of turns to spread the oil over the bore / rings.

The straight away, tip about 1/2 teaspoon of easy start (rocket fuel) down the plug hole - immediately reinstall the plug and try to see if you get a start.

?? Does the compression fell any better now
?? Does the engine start at all - even a couple of 1/2 hearted fires would be good

P/S - Whilst it may sound cynical - is there any chance your engine can see water - if so - I would put a coil of rope next to it - might scare it into action if it thinks it's about to become a boat anchore!!!_


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## MrChooks

Fix :wave:– OK we are going to have to get very systematic if we are going to defeat _Hirohito’s Revenge_.

Assuming that the oil in the bore trial mentioned in my earlier post – doesn’t work – and I would have been surprised if it does, as that only works with hopelessly worn bore / piston & rings; and I doubt your engine has that, given it started acting up all of a sudden – but at least that eliminates bore issues as the problem.

So the compression has to be escaping somewhere – and given you have had the head off to lap the valves – I am discounting a major crack in the head or total failure of the head gasket (as for that to be the case – a blind man with a white cane would be able to see the huge crack in the head or massive failure in the head gasket needed to cause you to have such poor compression) – so you would have noticed that when you had the head off.:laugh:

If I am correct so far – that only leaves the valves as a route for the compression to be escaping. And as you have lapped the valves – it must be escaping due to them not closing completely. So take the rocker cover off, remove the tappet (or otherwise disable the exhaust valve operating mechanism) and with the plug in, pull the engine through – you should feel compression on the compression stroke (one of the 4 revs it can take to get to compression TDC) and see if you have any compression now. If no, replace the exhaust valve assembly and try the same thing with the inlet valve assembly. My guess is that at least one of these is the culprit.

I doubt it is the valve spring – as it takes very little spring pressure to hold the valve closed and high compression valve springs are used to make the valves operate faster (higher revs) but as a rule, have little impact on the quality of the valve sealing properties.

If it turns out that it is the valves – you need to decide if you have set the tolerances correctly – if you have, it only leaves the “decompression mechanism – which I think is located on the cam shaft. I think Honda use a pair of weights and springs to make this work – so you are going to have to get into the guts of the engine to get to the cam shaft and see what is stopping the decompression mechanism from operating correctly – maybe a broken or dislocated spring or maybe as simple as a gummed up / stuck decompression mechanism.:4-dontkno

Fix – pls let me know how you get on – as _Hirohito’s Revenge _has now got me at the point where I think I will need psychiatric help.


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