Topic: Hondamatic top end upgrade choices

[Kongamatic]

Hi there,

I've read the topics on hondamatic performance upgrades and besides the round top carb upgrade I've also decided to upgrade my 1976 hondamatic with stock parts from a none hondamatic motor (pistons,head and cam). On a budget so I figure since I have access to 2 good top ends I could increase my compression and power with one of these 2 top ends. What I have access to is a 1974 K model top end or a 1978 F top end...by top end I mean everything above the block. Now I have access to both but I have to chose one has the owner of these top ends is trading me 1 of them for some stock parts...my question is which one should I chose? I've read that the F has different  oiling than the K but I read both that it can or can't be used on a K block so I'm confused.

I apologize if this has been covered in the past but after reading some posts I still need some guidance

Thank you in advance

Dom

[Jerry Rxman Griffin aka MuthaF'er]

The easiest way to properly use the late model F top end is the entire thing, cylinders, pistons, head and cam then you're OK. The downside to the F2/F3 head is the valve guides which wear quickly so that's something to watch for before installing.

OR - I'd keep the 392 head you have and use a late model cam. If your pistons are low compression ?? swap them out while you're at it. Maybe 77/78 K or 75/76 F. Also a cam from one of these engines would be an upgrade from the 74 K cam.

[Kongamatic]

Thank you, I was planning on using the entire set up of either one so seems like the F would be a better choice cam wise and yes I have low compression pistons now.

My only concern with the F was different oiling distribution I've read about...but if your positive by using the cylinders and head from the F will work I'll use that one.

Thanks again

Dom

[Jerry Rxman Griffin aka MuthaF'er]

The oiling distribution is the same. It's the return that differs. The F2/F3 head has only half the returns the other 750's have but the matching parts top end will work on the other 750 engines.

Don't forget the matching F2/F3 pistons too. 

[Kongamatic]

Awesome and thank you!

Yes I'll be using the pistons and rods from that same motor.

I'll be using round top...any guess on a ball park jetting I can start with?

[Jerry Rxman Griffin aka MuthaF'er]

The rods are all the same so you don't really need to swap those. The F2/F3 however uses better rod bolts but going down that road with the F2/F3 rods will possibly require new bearings. 10 X ~ $13.00 for crank and 8 X ~ $12 for rods. You could always swap the assembled F2/F3 crank with rods. That would probably eliminate new rod bearings. You'd need to compare engine/crank codes for crank bearing sizes for starters. If they are the same according to the charts use what's in the build engine but Plastigauge them for clearances. Sooooo, my take, use the original crank and rods and not really have to go through all this. Perhaps just use new wrist pins with the different pistons if it looks like there may be a problem.   

Not sure what the F2/F3 is jetted at but I'd do that for starters. Keep in mind the final jetting will depend on exhaust, carbs and air cleaner. 

[stikman]

For simplicity I'd go with the full K top end.  If I remember correctly, the intake boots for the roundtops won't work with the F head, different spacing.  I would prefer to run that F cam with the rest of the K top end.  But really, swapping in the whole K top end is going to up your compression from stock A pistons, and the K cam and roundtops are a real upgrade from the A as well.  I'd pass on the F head for the reason Jerry mentioned, they wear out the valve guides.

[Kongamatic]

Thanks guys I truly appreciate all the info!!

[stikman]

Not a problem.  Let us know how it goes.

[Kongamatic]

Will do!! This is where I'm at right now,waiting on dohc swing arm and shorty shocks then I'm I will start to Kong the frame....the front end is a yamaha xt250 with 21" drum gives me about 3" over...might rake it all depends on how it sits after the rear suspension mods and rear tire/rim choice which might be a solid rear rim

[Desert-SOHC]

What happened to your stock front wheel?

[Kongamatic]

Nothing,looking to build something different.

[kac3177]

I'd spend the money on an 836 upgrade. I build on a budget too however if you are going to do it, do it once... New pistons, rings and a fresh bore. The bigger cam and carbs will make a noticeable top end improvement, it did on my stock bore 76'

[Desert-SOHC]

Nothing,looking to build something different.

No, I'm interested in a 750A front wheel.  Did it have the stock one on it when you got it?

[Kongamatic]

Yes it was stock but unfortunately I just traded it for 77 K pistons and cam plus a few other odds and ends I needed.

This is where I'm at now....gonna start the Kong tomorrow.

[BPellerine]

you will not have much brake on that bike,small drum.bill

[Kongamatic]

Sorry I haven't been online lately but been busy getting my bike ready for a builders show I was invited too

Here she is....