The Hodaka Club Forum

I have this nice Webco head with three broken fins. Does this significantly impair proper cooling? Regardless, I'd like to have it repaired. Suggestions?

I don't have answers to your questions. Sorry. But I did want to comment that it appears someone cut the fins to run a high pipe. Is that possible?

Hey Dale, Maybe if it was just the two fins. I see the "tunnel"effect. There's a third fin knocked off almost at the base. I'm having a hard time imagining a scenario that would result in that kind of damage to the sheared off fin- other than some dude trying to rock the head off the jug with a pry bar. Maybe true/true and unrelated.

Ah, I see the third fin now. Dang!
I know that people fix this type of damage but I believe the hardest thing will be finding donor fins that would match.

Hmm...for better odds, I'll invest the effort in lottery tickets. Maybe someone has a roached out donor that has been shedding fins one by one.

Looking at the reflection in a store window, it will look great. I may be the only person that thinks it would not make much of a difference in cooling. They are a great looking head but I never thought there was a actual increase in performance. ------ Clarence

What Clarence said.
Ed

Thanks guys.

I have one on my 1968 Ace 100 Model 92 "Restomod"..
It is a High Compression with a Compresson Release on it.

It does make a Difference!!!!

Although this very subject has been debated here before (with excellent review of the variables ultimately determining BHP), my seat-of-the-pants tach gives Webco a ranking of "definitely peppier" than a matched bike with stock set up. I'd like to find that thread and read it again. A goodie as I recall.

It seems to me that anecdotal comparisons of different cylinder heads almost always fail to note the main characteristics which MUST be known in order to understand WHY a given head is deemed to be "better" than another. Did the two (or more) heads have the SAME combustion chamber shape, volume and placement? Was the squish band area also the same? Was the cranking compression the same? If those things aren't the same, how do we know WHAT made one head "better" than another. IF all those things ARE the same, now we can start guestimating whether thick fins are better than thin fins, sand cast better than die cast(?), heavier (more thermal mass) better than lighter (less thermal mass). Ya know . . . ?

It seems like we are discussing three different things. There seems to be some consensus of anecdotal evidence of a "seat of the pants" performance enhancement from the Webco head over stock. What is more difficult to assess is whether there is difference in cooling effectivity. The "coolness factor" is a matter of personal preference.

Good point Pop. Is the Webco head better because its combustion chamber and squish band improves performance ? Or is it better because the thermal mass and/or fin design is just right and it cools better? Or does it look so cool that it just has to be better? (There is no denying the visual coolness factor. )

Ed

I had a bunch of DG modifications (including a head) on my CR125 back in the early to mid 70s. I know, I know, it's not a Hodaka,... and it may not have made any difference in performance... but it made me feel faster!

Have them milled to look nice and then mill the same three on the other side to match.

Hey, somebody answer a quick question for me and I'll get a bit of data together. All other factors being constant, does over-boring the cylinder decrease the maximum pressure generated at TDC? My recollection is that it does not, at least to a significant effect. Thanks guys.

PS- I like the idea Kelly. Then I'll put it on my Super Rat and tell everyone it is some super-secret $4it.

I'm not sure what might have prompted the question. Following the assumption stated in the question, the cylinder head, head gasket and engine stroke stay the same and only the bore changes (gets larger). Let's calculate it out.

Standard bore 100cc Hodaka - 50mm bore X 50 mm stroke. Displacement equals Pi X radius of bore X radius of bore X stroke (we'll convert mm to cm right at the start to make the end result be in cc's)

3.1416 X 2.5cm X 2.5cm X 5.0cm = 98.175cc
- - - - - - - - - - -
4th over-size bore or + 0.040" overbore = 51mm bore (5.1cm bore diameter = 2.55cm radius of bore)
so
3.1416 X 2.55cm X 2.55cm X 5.0cm = 102.14cc
- - - - - - - - - - -
So, displacement has increased by just a hair shy of 4cc's. That is an increase in displacement of four percent. With no change in combustion chamber shape/volume, cold cranking compression will go UP a little bit. Sorry, I can't tell you how much - but it WILL go up slightly.

Hope these calculations are helpful.

Ed

Excellent Captain. That is exactly what I was hoping for. Something I plastered up there in about 1980 must have covered up Pi x r x r. For kicks, I'm going to whip out my cylinder pressure gauge for a little A vs B what's what. 2nd vs 3rd overbore is the variable of concern. No longer the case. Thanks Captain

Yer talking about something on the order of a 1% change on a single step of over-size bore. The change in cranking compression may be "lost" in the "noise" of the other variables. Are the exhaust ports on the two cylinders at EXACTLY the same stroke height? Are the rings sealing equally well in the two cylinders? (same end gaps, same "ring seating" condition, same cylinder bore finish). It will be interesting to hear what you find.
Ed

To me the biggest factor for engine compression has been the break in, some people are just gifted at such things. Night and day difference. ------------ Clarence

A question for y'all, please. I think through it and reach a conclusion one way, then think about it differently and conclude the opposite. In other words, I've confused myself, which is not an unusual situation. Talking 2 cycle engines, should the volume calculation (for compression - not for displacement) use the full stroke like a four cycle, or would it be more "accurate" to use the distance traveled from the top of the exhaust port to tdc?

-Stever

The actual compression stroke on a 2 stroke is indeed only from the top of the exhaust port to TDC(Top Dead Center).
Ed