OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Smokey Honda GX160

Hi,

I have subscribed to the Lawnmower manuals section, but there is currently only an owner's manual. Does anyone have the full service manual that can be uploaded?

My GX160 has been starting to blow a bit of smoke and it is progressively getting worse with time, so I have ordered a new set of rings and a full gasket kit for it.

While I've got the engine apart, I'll lap the valves as well. Is there anything else I should be doing while it's pulled down?

Thanks in advance...

Ben.

Ben, the first question is why you think the rings are worn. Have you tried putting a spoonful of engine oil into the spark plug hole then pulling the starter cord, to see if compression has substantially increased? If it has, you need new rings. If it hasn't, you probably don't. Is the smoke from the engine blue? If not, it is probably not oil smoke.

Should you decide you need to replace the rings, I suggest you service everything covered in the owner manual, clean the inside of the crankcase, inspect the crankpin and connecting rod big end, and test the ignition, the only other thing you could consider doing is cleaning out the carburetor. I don't actually recommend that though, unless you've had considerable practice already. The average home mechanic probably does more harm than good to carburetors, unless they are actually misbehaving. Why not replace the rings, service it, then try it to see if everything is working properly? If you aren't satisfied with the way it runs, let's talk about the likely causes and some targeted work to put it right.

Thanks Grumpy.

The smoke is bluish white. It got noticeably more obvious after the last oil change which was ~6-8hrs of operation ago.

It also puts out a small cloud of black smoke and momentarily drops the revs if the engine is throttled up quickly, but I assume that is just the governor pouring fuel in trying to catch up.

The engine starts first pull every time and runs/idles fine. A car mechanic friend said if the smoking is just something that progressively gets worse over time, it could be rings or valve guides.

I'm open to any suggestions on what else it could be or I could try.

I'm downloading the owner's manual from Honda now.

Ben.

The black smoke on sudden acceleration is normal, as you thought. The bluish white smoke is not typical of worn rings, it is usually just blue. Have you tried the oil-in-the-plughole trick? If it does not improve your compression substantially (so you can feel the difference when you pull the starter) it sounds more likely you have leaky valves. You might try checking the tappet clearance: if one or both valves has little or no clearance, it is very likely they are leaking. The whitish smoke is probably a better fit for leaky valves than for leaky rings.

Another possibility is the oil that you put in - either quantity (overfilling will cause smoke), or quality (cheap multi-grade oil should be avoided as if it caused social diseases)

Good points, igor. Note that Honda, unlike Briggs and Statton, recommends the use of good-quality modern automotive multigrade oil in their engines. That would make the design, fit and condition of the piston rings more important than on Briggs engines if you are to avoid excess oil consumption.

Thanks guys.

Oil level is definitely correct as per the manual and oil quality is very good...it is the same Motul engine oil I use in my Honda motorcyles. I treat my tools the way I treat my bikes...if it is fuel, oil or some other product I wouldn't use on or in my bike, I won't used it on my tools. That does bring up another point though, would using high octane fuel (I use BP Ultimate exclusively in my bike and power equipment) have any bearing on this? My MTD 4-stroke (B&S powered) rotary mower has no issues with it, nor does my Stihl 2-stroke blower or my Honda 4-stroke brushcutter.

The gasket and ring kits should arrive in the next couple of weeks, so we'll see how they go along with a valve lap, tappet clearance adjustment and an oil change.

Ben.

You should not need high octane fuel in that mower engine. One point I should explain, though. Honda's pushrod overhead valve, and overhead camshaft, engines (yours is pushrod) have much higher compression ratios than both Honda and Briggs & Stratton side valve engines (either 8 or 8.7 to one compared with 6 to one). Hence there is quite a lot of nonsense you can get away with on the side valve ones that is not to be considered on the OHV or OHC ones. Also this is why your small engine (160 cc) has an automatic decompressor, which small side valve engines do not.

Honda specifies at least 91 Research Octane Number (RON) fuel for your engine. That is the specification of standard unleaded in Australia. Premium unleaded is 95 RON. Use of Australian premium unleaded fuel in your engine should not cause any problems but is not required and is unlikely to produce any benefits.

Well, she wouldn't start at all today...bugger! I checked the carby bowl, oil level (because the engine has a low oil cut-out), etc and it was all OK.

Pulled the spark plug and here is what I found - click for larger images:



Gave it a good scrub with a wire brush and checked the spark and it was good. Put it back in and she started first pull.

While I had the plug out, I also put a spoon full of oil down the plug hole and put the plug back in and checked the compression - there was noticebly more compression with the oil in there.

I also noticed that the muffler has a couple of rust holes in it, so I'll replace that when I do the gaskets, etc.

So she is running again, but then the bloody clutch burned out (it is mounted on an SB 17" Model 45), she is totally offline at the moment while I get some new cork.

Ben.

Ben that spark plug only got that way from burning oil. Coupled with the improvement in compression when you did the oil-in-the-plughole trick, it seems clear you are in need of new rings. (It is even possible you will find the rings are broken, and if so you will probably need a new piston.) It is good practice to lap the valves when you replace the rings - it is likely to save you having to do it later, as a separate job. (I notice you have ordered the rings, and intend to lap the valves when you install the new ones.)

Please keep us posted when you do the work, including the clutch re-line. Some pics would be useful for other members, and for the archive.

OK...all the bits have arrived, so I'll be taking the mower up to my sister's boyfriends workshop (he runs his own car mechanical business, so he has all the tools we'll need to do it) on Sunday to do it all - bore hone, new rings, full gasket kit, valve lapping and cleanup, new spark plug (the old one gave up on the weekend), oil change, adjust tappets, etc.

He said it may be worth doing the valve seals as well. Does the GX160 have valve seals? I haven't seen them on any parts lists.

Also, does anyone have the full service/workshop manual? I have downloaded what is available of this forum and from Honda and the Honda one has the tappet clearances, but not torque settings, etc.

Also, if someone wants what I have to upload to the manuals section, let me know.

Ben.

Ben, the parts and manuals section has the full workshop manual for the 194 and 214 Honda mowers. The 194 and 214 have the GXV120 engine. With Honda model numbers, the G means Honda, the X usually means pushrod, and the number is the capacity in cc. The V, if it has one, means vertical crankshaft. No V means horizontal crankshaft. The GX120 and GX160 engines are rather similar except for bore, stroke, and fuel tank size. (They both use the same owner's manual.) The horizontal and vertical crankshaft basic engines are quite similar except for specifics like the oil slinger arrangement and the oil sump. So, you can probably get the information you want from the HR194 workshop manual, which is fairly detailed. Incidentally it does not show or mention any valve stem oil seals. I don't personally know of a mower engine that has them.

If possible, when you do the engine repairs please take a few pictures and post them here. In particular, if you can measure the piston ring gap with the rings inserted into the bore 10 mm from the top (use feeler gauges), and show how the ring grooves in the piston look before you clean them, that will make this thread more useful to other members as an archive. It helps people to get a sense of perspective if they know how much ring gap it takes to give lousy compression and heavy oil consumption.

Don't forget to check the fit of the valve stems in the guides - details of sizes and clearances are given in the workshop manual. You can also get the dimensions, and a way to measure the stem clearance, in this thread:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=23913&page=1
If you measure the valve stem clearance as described in the other thread, please post a picture of your setup.

Hi morphias, The info that you have downloaded would be great for the Parts Lists and Manuals area, could you please send Bruce a PM (just click on his name, scroll down to "Contact Info" and click "Send a PM") and ask for his e-mail address to send the material. He will then upload it to the correct area.
Many thanks mate,

Well...pulled down the engine yesterday and made a few discoveries.

Whoever have done the job of repowering the mower did an 'average' job. It was clear that the drive shaft had no had grease or anti-sieze applied to it before installing the clutch, so the engine side of the clutch housing was well and truly stuck to it.

Being made of allow, it meant great care had to be take not to crack or break it. Copious amounts of Inox was applied and left to soak with no change - she was stuck fast. We heated up the housing with map gas and put a clutch puller on and with a very careful combination of applying some load via the puller and then tapping the housing along the shaft with a block and hammer, we got it off millimeter by millimeter. The better part of an hour later, we had it off unharmed.

Needless to say, the oil seal got fried, but a spare was luckily obtained out of a small box of Honda odds and ends from the Stihl dealer that backs onto my mates workshop. There was an amount of surface corrosion on the shaft that prevented removal of the side cover of the engine because the crank case bearing could not get past the rust. We carefully sanded this off with some emery tape, which of course trashed the crank case bearing - it is open bearing. I'll source a new bearing today - the mower shop and Repco up the road had the right bearing, but only in a sealed bearing. We'll be sure to linish the shaft well and reassemble it with anti-sieze to make life easier in the future.

The piston was fine, but the bore was well glazed. One look at the rings and we knew they were stuffed - we didn't realize stuffed they were till we checked the end gap with them in the bore - the service limit on all 3 is 1mm. The oil ring was 2.73mm, the top ring was 3.42mm and we gave up on measuring the second ring at 5mm!

On to the head, the valves had large amounts of build up on them...clearly a result of excess oil in the chamber. The exhaust valve also had evidence of oil coming through from the valve guide as well. With the rockers and valve srings out of the way, the intake valve felt very good, but the exhaust valve had significant excess lateral movement - this proved that oil was getting down the exhaust valve guide, which would have been exacerbating the smoking issue.

Valves guides are not a listed replaceable component in this engine, although guides can be bought for them at $7.60 USD, but then you have to fit and ream them to suit your valves. At this point, things are not looking so good. A quick look on eBay brought up a few cylinder heads for the GX160 - the GX160 is a very popular go kart engine in the USA, so parts are very readily available over there.

http://cgi.ebay.com/Honda-Replaceme...t=LH_DefaultDomain_0&hash=item3caf732dd4

This one looked to be the best one out of what was available and meant a totally new top end for the engine. For the $$$, it was worth a go. Even if it turns out to be average quality and I go through one every 18 months to 2 years, I would consider it an acceptable price and a consumable component. I should have it landed here by Friday with any luck.

I forgot to take my camera on Sunday, so I don't have pics of the valves before we started cleaning them, but I will take it when I go back to finish the rebuild and take photos of the new and old rings in the bore so you can see the massive difference.

On the topic of rings, the new oil ring I have a is a 3 piece job, whereas the original is a 1 piece. Does this matter? The rings are made by NPR, who are the manufacturer or all OEM rings for all Honda engines. Maybe they just changed was is fitted over the years?

Before we put the engine back together, all of the components (block, crank, etc) will be put through this industrial parts washing machine he has at his workshop - dirty parts go in and come out looking like new.

Everything had the hallmarks of a lack of knwoledge/care/maintenance - I went through similar things when I was restoring a 1963 Morris Mini - you just don't REALLY know what you have till you completely pull it apart.

Ben.

Remember, Honda has published size limits for the valve stems and the bores of the guides. If you measure the stem of the exhaust valve, and measure how much it moves in the guide, you can calculate the size of the valve guide bore, as explained in this thread:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=23913&page=1

Is the three piece oil ring you looked at a steel rail ring set? This type of composite ring has two steel rail rings, which are flat thin steel rolled on edge to make piston rings about one mm thick, and they are installed with a ring expander also made from thin flat steel. The expander both holds the rings edge-on to the bore, and applies outward pressure to them. Just about all car engines except British ones have had steel rail oil rings since WW2, but most British cars didn't use them until about the 1960s. They are far more effective than cast iron oil rings in controlling oil consumption, but they are more expensive to make, and I don't know how they would perform in aluminium bores. If Honda sells them as "genuine" replacements, I think you would be safe in using them.

Have you checked the bore size, underneath the ridge at the top of the stroke? With the rings so worn, there is a good chance the cylinder will need a rebore. Putting new rings in heavily tapered cylinders is seldom successful.

The rings use an MF style spacer. Two thin steel rings with a nitrided 'wave' spacer.

http://www.federalmogul.com/korihandbook/en/section_24.htm

The box is factory stamped as being for this engine, so they should be right. I see most ring sets for Honda's are the same style now.

We don't have a dial guage, but I can confirm that the 'slop' in the exhaust valve guide is noticeabley bad. The valve stem diameters are well within service limits.

The bore is also well withing service limits and there is no discernable step from 10mm down the bore to the top - I'll have to write down the numbers when I am next at the workshop.

Ben.

Those are fairly conventional steel rail rings, but neither the VS nor MF type of expander is a popular type as far as I am aware. The SS55 type was locally made by Repco for a while. It was much cheaper than the other types but is an extremely poor design. I fitted a set to my V8 MGB when the bores were worn to 0.010" taper, and after 3,000 miles five of the eight expanders were broken. I fitted a more reputable expander type to the same steel rails, and it was still working well and not using oil after 30,000 miles when I sold it. It sounds as if you are buying an after-market ring set, not a Honda ring set. I wouldn't do that myself, unless the engine has a cast iron cylinder liner. The required ring pressure for an aluminium bore may be different from an iron bore, and steel rail rings behave quite differently from cast iron oil rings.
Post-edit: The GX160 engine has a cast iron cylinder liner, so there is no problem using steel rail rings.

You can overcome not having a dial gauge by using feeler gauges to measure the valve head's lateral slack. Just clamp a piece of metal with a flat face parallel to the valve stem, to the inside of the cylinder head. Push the valve head toward it, slide the metal piece close to the valve head and clamp it, then measure the clearance between valve head and flat metal piece with feeler gauges.

Because your valve stems are not worn, and you only have noticeable slop in the exhaust valve, not the inlet, it does sound as if the exhaust valve guide is worn. Honda only allows 0.005" of wear in the guides. The guides are replaceable on the GXV120, which I think has the same cylinder head design as the GX160, though I am not certain about this. Why do you believe they are not replaceable in your engine?

The rings are not Honda branded, but are produced by NPR (Nippon Piston Rings) for the GX160 engine. NPR produce the rings for the Honda engine factories and parts stores.

I spoke to the Honda dealer down the road and he said that this is how they come now (3 piece oil ring) whether you get them with the Honda logo on the box or not - but in typical Honda fashion, you pay an extra $20-30 a set for the Honda logo on the box.

I did say the guides were replaceable, but compared to the cost of a complete head kit, it is not economical to change them out. The Honda guy said he hasn't bothered doing guides for over 20 years now - the cost of the guides and then the labour for fitting them and reaming them to suit the valve stems is more expensive than a new head...a genuine head is ~$100. I got a non-genuine complete head kit for $93 delivered from the USA - the GX160 is the most popular go kart engine over there, so there a heaps of after market parts available. Just going through the sellers catalogue, I could build a complete GX160 from new parts for ~$350-400. e.g. Crank case and cylinder $50, crank $35, complete head $65, cam components $35, ignition coil $35, gasket kit $20, recoil starter $20, piston and con rod $40, carby $15, exhaust $20, fuel tank $20.

I'll measure the slop in the exhaust valve, but the 'feel' of it indicates a lot more than 0.005".

I have the full workshop manual and parts list now - been trying to get them to Bruce to upload them, but his mailbox is too full.

Ben.

Thanks Ben, that sounds good. If you can get high quality factory-rebuilt or new heads, delivered in Australia, for under $100, I am inclined to agree that is cheaper than having a dealer recondition your old head. Provided a nominal-size (i.e. same stem diameter as new) exhaust valve actually has more than 0.005" slack in the guide, the only cheaper solution would be to find a junked head with decent valve guides locally.

Hi guys,

FINALLY got time to rebuild the engine.

Mate...talk about a saga...when you get something second hand, you never REALLY know what you have till you pull it apart.

The piston and bore had almost no wear making them well within service limits.

The new head is excellent and the engine have gone back together with all new seals, bearing and the new head. All gaskets surfaces were cafefully cleaned and polished, gaskets greased, new component assembled with assembly grease, new valves adjusted and all old components well cleaned, the carby was given a thorough clean and all bolts and nuts tightened to correct torque settings. Compression is now almost the same as new.

The output shaft was carefully linished and a good dose of copper anti-sieze applied to stopped the clutch housing corroding and locking on to it again. The same was done on the mower drive shaft.

The woodruff key on the drive shaft side of the clutch housing had snapped and the groove was well flogged out. We fabricated a new key and built the groove back up with the mig and ground it back...looks like new. The engine is mounted on a Scott Bonnar Model 45 that is a total bitza - some really dodgey home handyman fixes have been applied to it by the previous owner and it appears to have been poorly maintained...this was also evident with the engine. I am currently on the hunt for another Model 45 to move the engine to and use the current one for parts...not that there are too many good ones on it...but hey, it was free and it actually cuts really well. The cylinder blade is almost shagged though, so that is a big motivation to find another frame with a good set of blades. Missed out on an awesome bargain on the weekend due to being stuck in the workshop. An 8yr old Rover Mod 45 went for $122.

Anyway, I started the engine for the first time yesterday and ran the new rings in with a good quality 30 weight mineral oil. The engine fired on the first pull and sencond pull, but did not run. My new, recently purchased, Honda brushcutter does the same thing if the choke is used - it doesn't need the choke to be started. Turns out it was the same thing with the GX160. As soon as I turned the choke off, it started first pull, so I assume that the engine is essentially new now, it doesn't need the assistance of the choke anymore.

The engine run much smoother, there are no leaks and is significantly quieter than it was before - in terms of both mechanical noise and exhaust note. It is also much more ballsy in power delivery than it was before - I didn't realise how tired the engine actually was before till now and she idles beautifully. Oh...and no smoke anymore!

I'll change the oil out after a couple of hours operation for good quality multigrade oil, but so far, I am very happy with the improvement.

In terms of parts and consumables, the engine owes me ~$170 including the carton of Coronas for my mate whose expertise and workshop I used for the project.

Now that the clutch and engine can be easily separated, maintenance will be a whole lot easier. I'm kicking myself for not replacing the clutch cork while I had the clutch off - I had the new cork sitting there - but that is an easy job I can now do at home.

Sorry I don't have any photos - apart from the fact that I forgot the camera, I probably would have forgotten to take the photos anyway.

Time taken was a bit over 6hrs for mower and engine disassembly and ~7.5 hours for cleaning, fabrication, repair and reassembly...and that was with two experienced guys working on it. If you didn't have the skills, tools, etc and had to take it to a mower shop, it would not have been a financially viable project. If the mower and engine had been well maintained, I think the whole lot could have been done in half to 3/4 of a day.

Ben.