Squish Question

[Dr. Frankenstein]

I came across an interesting thing this afternoon when I took my head in to have the valve seats ground - the Intake valves are apparently Not the original valves - just the Intakes, not the Exhaust valves -

And the domed part of the head the valves sit in, the combustion chamber, if you will - the edge that goes around it (the Squish section) is slightly deeper - maybe 1 or 2mm - than a spare head I brought with me for the same purpose. Grab a beer or have a smoke, it's Backstory time...

OK, so the bike I'm working on now is the bike I've been talking about in my posts - a 1962 Honda CA77 305, so it's an Early model. The *spare head I have I believe came from a Late model 305...the Spare head also has a piece of metal missing from the flat surface around the inside rocker arm channel hole - the rocker arm hole itself is fine, but its just like a small divot has been taken out of the surface where the hole goes through the head...it looks like a bullet hole(I'll try to post some pics later). My mechanic says that's fine, it's not interfering with the rocker arm hole at all, it just looks rough.

I got the Spare head's valve seats ground out fine. 45/30 degrees....But in doing my CURRENT bike's head, my mechanic noticed the Intake valves were a bit too small for the new seats we ground, and sure enough: when compared to the original intakes on the Spare head, the Original Intake valves were noticeably smaller and totally different! ( Just the intake valves - the Exhaust valves of my Current bike were identical to the spare head's exhaust valves).

OK, so now for the Squish part: the squish section/combustion chamber edge of the Current bike is noticeably deeper than the Spare head squish section. My Question IS: if Honda made the (pretty much) same engine for ten years for these bikes, how critical is that Squish area if I want to use the Spare head on my Original engine? Not much, I would think, but I thought I would throw this out there for comment...

The "Mystery" intake valves have an "A" on them - any idea what they could be from, and WHY someone would put in SMALLER intake valves?? They're not exhaust valves - they're just smaller intake valves...??

[DJM]

Pretty sure early Dreams had small inlet valves marked A

Later I think C/CA engines used the same size inlets as the CB and CL models, now marked B

Checking in the parts books should confirm parts change although not the sizes.

Others may know more?

[Dr. Frankenstein]

They sit really deep in the seat as compared to the newer model valves - are they supposed to? And they Are smaller than the Late model valves...is that right?

[DJM]

Could it just be that you're trying to fit 'small' valves into a head that has had the ports and seats cut for the later large CB type valves.

The damage to the rocker arm pin area of the head was probably caused by someone trying to fit an inlet rocker arm pin to the exhaust valve position. Inlet pins are 0.5mm bigger at the inside end so won't fit. I've seen this type of damage before.

[rrietman]

early engines had smaller intake valves. why are you wanting to use the later head on this engine? I've never done the swap but on paper it should work.
Good luck
Randy

[Dr. Frankenstein]

Well, depending on what is determined about my Early head, I still may use it -I do like to use the original parts the bike came with if I can. We ground the valves on both heads at 45 degrees, and then 30, thinking they were the same - I'm just worried that because of the apparent difference in the ports of the Early bike and how pitted they were I may have ground them too much - but it was done under the supervision of a certified mechanic with over 30 years experience in a professional shop, so, Maybe...? (The spare(Late) head was beautiful, it just need a light touch-up).

Also, if I recall correctly, no matter what year the bike is, I think they are all 30-45-90, right? So it might not matter, and if so, Great! I like to use original whenever possible, regardless of patina unless it's really bad...but he pointed out the two Early valves looked nothing like the Late valves, and he's right - the Early ones are noticeably smaller - I just want to make sure they are the correct part, and not the product of some past botched attempt at engine repair.

Every engine tells a story, and just look at the clues: possibly different/smaller intake valves, the two stuck pistons I had to pound out with a chisel and a sledgehammer, the cracked piston sleeve, the divot around the rocker arm hole; and all the nasty *Black goopy oil I gukked out of the cases...to me it indicates bad oil flow and subsequent piston seizure, but I am no mechanic so I could be/probably am wrong. I certainly hope so...

[DJM]

Using the early head and smaller valves just might be a shrewd decision.

Over the years I've spoken with quite a few guys who've owned these bikes, some have owned several, and the consensus seems to be that the early bikes were noticeably quicker than the later ones.

As well as being smaller the early valves had a very different profile at the back of the valve head which could have given better breathing, fitting larger valves doesn't automatically mean more power, there is an optimum beyond which any potential gains actually become losses, it's about gas speeds rather than just valve sizes.

Given your desire to keep as much off the original bike as you can I'd go with the earlier head with the small valves, I wouldn't worry too much about a bit of pitting in the combustion camber or ports so long as the valve seats themselves are good and sounds like you mechanic has that sorted.