Top end rebuild

[CaptCanadia]

Last year I rebuilt part of my Honda clone. I put an extended con rod, racing cam, billet flywheel, and stiffer springs. Do you think a $120-$150 investment in the top end will yield a reasonable power gain? I was thinking of swapping out the push rods, 26 lb springs(currently 18), 1.2 rockers, and new valves(not sure about the size). My assumption is that this would hardly make a noticeable difference.

Also, I'm assuming a flat top piston would be well worth it? Any insight would be much appreciated, thank you

 

[tha_thrasher]

Have you thought of just swaping to the gx160 head, its only 20-40$ on ebay

 

[CaptCanadia]

I thought about it, but then I'd also need a new gasket and cover head. I think getting it milled down would probably be more beneficial. My concern though is that something in the stock top end might blow from the massive increase in RPM.

 

[Half-breeder]

Last year I rebuilt part of my Honda clone. I put an extended con rod, racing cam, billet flywheel, and stiffer springs. Do you think a $120-$150 investment in the top end will yield a reasonable power gain? I was thinking of swapping out the push rods, 26 lb springs(currently 18), 1.2 rockers, and new valves(not sure about the size). My assumption is that this would hardly make a noticeable difference.

Also, I'm assuming a flat top piston would be well worth it? Any insight would be much appreciated, thank you

A flattop piston, bore +.020 and a gx160 head(much greater compression ratio) would add bout 2(maybe 3) hp...

Springs would just be for a higher RPM(not recommended going to a 26lbs... useless upgrade if using same carb. Right now your carb is the 'limiter' of your RPMs).

A carb w/ a larger diameter outlet... port n polish the head ports(both intake and exhaust)=2-3hp.

Larger valves 'could' maybe add a (1)hp(but not enough to tell by just 'that' change alone).

New pushrods(unless they are lightened) yield no +hp... just a slightly faster acceleration... again not enough to tell.

Im probably wrong bout the +hp amounts... but Im just passing info I somewhat remember seeing somewhere.

 

[CaptCanadia]

Thanks for that idea. I forgot to add that it does have a 22mm mikuni carb on there. With that carb do you think the springs would yield something?

You don't think that stock push rods could be bent at high RPM?

 

[Half-breeder]

Thanks for that idea. I forgot to add that it does have a 22mm mikuni carb on there. With that carb do you think the springs would yield something?

higher rpms... 26lbs springs I think (probably wrong) yield around a 9-10k range of RPMs

 

[CaptCanadia]

That sounds scary to be sitting in front of Thanks for the info.

 

[CaptCanadia]

Does anyone know the max lift of a GX200? I asked this before, but never really got an answer. I think I am going to get a 14cc head and mill it. Does anyone know how much can be taken off in regards to valve clearance? I have a con rod (.020 longer than stock) and I'm thinking a head .020 longer than stock with Dyno CM .265 lift.

 

[OzFab]

Not sure exactly what you're asking but, to determine the max possible lift, bolt the engine together with all the milling work done, set the piston to TDC, remove the valve springs &, using vernier calipers, measure how far the valve can drop before it hits the piston; you'll need to do some subtraction to allow for clearances but, remember, what you lose on the piston you gain a bit with the valve spring tension...

 

[CaptCanadia]

I must be asking a stupid question lol. What I'm trying to ask is, can the head be milled down too much so that the valves strike the piston?

 

[Half-breeder]

... can the head be milled down too much so that the valves strike the piston?

Can?... oh yea. If you mill down the head too much your pistons will end up . In order for that to 'not' happen a 'groove' can be ground out of the piston top(not recommended) for clearance of valves. "This" process is done to high reving motors that have great amounts of compression(in autos).

 

[CaptCanadia]

Yeah that doesn't sound very nice lol. That being said, does anyone know a safe amount I can get it milled so that this doesn't happen? Would 0.065 be safe with my above set-up?

 

[zbuck]

Not knowing if the piston is in the hole a TDC or level with the block. If your going to add .020 to the stroke and mill the head .065, that is .085. In my estimation your going to have some piston to valve clash, not good.

 

[exenos]

If you dont hit the valves with 85 thou taken off you may run into problems with detonation on pump gas.

 

[CaptCanadia]

Ya I thought about that too. What do you guys think is a safer number?

Also don't forget the head is .020 longer too. What do you think about .025? Would it even be worth milling?

 

[Half-breeder]

Ya I thought about that too. What do you guys think is a safer number?

Also don't forget the head is .020 longer too. What do you think about .025? Would it even be worth milling?

Its doubtful anyone is gonna be able to tell you an answer to 'that' question... that's one of those things your gonna have to have 'in hand' w/ a measuring tool, while moving the components... or take everything to the machine shop... and have them looky see. Honestly IMO, even 'if' someone gave a numerical amount to mill... I wouldnt go by 'that'... youve gotten to the point where detailed info can ONLY be answered by you(or someone physically round you, w/ the parts in hand).

Little bit like someone asking... "Should I marry her...?" (we could ask her ex-bf... but can you REALLY go by what they say... even if it's all true...?)