gx160 build

[scruffyface]

Hello All - I am complete newbie to engine building and trying to figure out where to go for good info. Any websites are appreciated.

I ripped apart a gx160 to rebuild with my son before buying the cart. We were just going to remove the governor and put things back together. But in doing more research and now that I have it apart, I am thinking I should do more work. So it looks like I should definitely replace the connecting rod. Keep in mind while my goal is not to build a super competitive kart, I would like be consistent with WKA regs in case we decide and find a place that my son wants to race.

So first set of questions...
1. It looks like I can get the connecting rod (and/or cam shaft) in different lengths to improve compression and of course cam shafts with different lift rations. Not sure how to determine what the variables would be to determine the best length and/or cam shaft.
2. Should I switch to a flat-top piston?
3. How do I determine the correct spring tension or does it really matter as long as it is better than stock.
4. Any thoughts on where to look for parts? I have found a couple websites and of course there is e-bay and amazon. But other suggestions are appreciated.

It looks like some other mods may give some initial easier performance, but as I am working on building with my son we are working from the inside out to help him understand the mechanics of how the engine works, and just to get his hands a bit dirty.

Thanks in advance for any help!

 

[DirtyDamage]

Good links for all sorts of stuff check it out for sure

Try this website for specific Honda parts...

Good Tutorials

 

[scruffyface]

Looks like a few more late nights... awesome, thanks!

 

[Poboy kartman]

Welcome to the forum!
Please fill out a profile location so it will show you're in Connecticut in the upper right of your posts.

 

[OzFab]

Well, DD answered some of the more important questions but, just to cover what he didn't...

1. It looks like I can get the connecting rod (and/or cam shaft) in different lengths to improve compression and of course cam shafts with different lift rations. Not sure how to determine what the variables would be to determine the best length and/or cam shaft.

Changing the length of the conrod also means you will need to change the piston to match; right now, the length of the conrod means the piston sits almost level with the top of the block; if you replace the conrod with one that's, let's say, 3/16" longer than stock, that means the pitson will protrude past the block by 3/16" at TDC...

As for cams, each cam has different characteristics, depending one what you want; some produce more power at high RPM, some produce more power at low RPM & then others produce more power in the middle of the range; the best thing to do is first determine what characteristice you want, then talk to a supplier, they shoud be able to guide you as to exactly what cam you need...

3. How do I determine the correct spring tension or does it really matter as long as it is better than stock.

The correct valve spring tension, again, is relative to your needs but, the other internals used should be considered when deciding what springs to use...

At the moment, your post contains a lot of "I think", "maybe", "should I"; as a result, the above information is about as deifintive as it gets until we have more solid information

 

[scruffyface]

Fabroman - thanks! This is the kind of info I am looking for. I am really more interested in understanding the "whys" of things versus just building something based on what people tell me.

So in looking at the height of TDC. It should not change? In the reading I did, it seemed that by increasing the height of TDC you would increase compression.

Can you give a bit more information about Cam characteristics? (e.g., concave v. flat or anything else relevant).

Same for valve spring tension...what are general rules of thumb.

Related the "I thinks". Obviously, the build would depend on where and what type of racing, which I am unfortunately not sure of yet. When racing picks up again in Sept, I will stopping by some local track to learn more about this. For the time being, I am "thinking" that we would be most concerned with the mid range.

Given the uncertainty, it probably makes sense to hold off on changing the internals substantially. Other than removing the governor are there other internal things that I should be doing that are inexpensive. Then I will move on to intake and exhaust.

 

[DirtyDamage]

If you really want to toy with an engine I suggest getting a predator engine from HF and building that. If you mess something up it can be replaced for like $10 for whatever part it was.

 

[OzFab]

So in looking at the height of TDC. It should not change? In the reading I did, it seemed that by increasing the height of TDC you would increase compression.

If you use a longer conrod with the standard piston, YES IT WILL! Whether it's a few thousandths of an inch or a few hundredths of an inch, TDC will change; by what amount TDC changes could mean the difference between the piston missing the valves & the piston breaking the valves...

Yes, increasing the piston height at TDC will increase the compression ratio but, as with any engine, there is a point at which you start going backwards... as in, you no longer gain performance, you lose performance because the mods are simply too much for the engine to perform efficiently...

Can you give a bit more information about Cam characteristics? (e.g., concave v. flat or anything else relevant).

Unfortunately, I do not know enough about cams to pass on any useful information...

Same for valve spring tension...what are general rules of thumb.

Stock valve springs are good to around 5000rpm, at which point, they are not strong enough to close the valves efficiently & you have what's called valve bounce; effectively, what happens is, because the valves are opening & closing around 80 times every second, the springs can't keep up & fail to do their job efficiently, allowing the valves to stay open when they should be closed...

Heavier valve springs prevent this from happening; the heavier the spring, the higher the RPM limit...

However, heavier valve springs is the last mod we suggest, after a billet conrod; I mentioned

Stock valve springs are good to around 5000rpm

Well, the stock conrod is only safe to around 5500rpm; if you install heavier valve springs that will allow the engine to rev to 7000rpm, what do you think the stock conrod will do? Just last week we saw an engine that had heavy valve springs installed with a stock conrod & it wasn't pretty...

Given the uncertainty, it probably makes sense to hold off on changing the internals substantially. Other than removing the governor are there other internal things that I should be doing that are inexpensive. Then I will move on to intake and exhaust.

That sounds like a good idea; do some more reading so you can better understand what you currently don't understand; reading the proper information will give you a better understanding of how the different individual parts of an engine work with & interact with each other, giving you a better understanding of what you can & can't do safely...