Topic: combustion chamber CC's + Summit compression ratio calculator app.

[Don R]

  This may or may not be accurate, but I gathered it here over time and compiled it when I cleaned up my notes. Updated from checking mine and input here.
   Stock combustion chamber sizes. Contrary to previous reports there is no 26cc stock chamber. I can't find proof of a #405 head.
   
   Edited version

   300 series heads 22 to 23cc
   392 Hondamatic  24cc
   392 F0/1            24cc
   392 K7/8            24cc
   410 F2/3            28cc

[MRieck]

  This may or may not be accurate, but I gathered it here over time and compiled it when I cleaned up my notes.
   Stock combustion chamber sizes. I believe all 392 heads to be 24cc but I haven't checked them all either.
   
   300 series heads 22 to 23cc
   392 Hondamatic  23cc
   392 F0/1            24cc
   405 K7/8            26cc
   410 F2/3            28cc

Looks good Don though I don't know if there is a difference between the Auto head and the F/K 392 heads. FYI I had to take -.045" off an F1 392 head to get the 21.1 cc's I was looking for 71.25 flat top pistons. I was looking for about 10.5:1CR with .040 squish.

[scottly]

The K7 also used the 24cc 392 head.

[Don R]

The K7 also used the 24cc 392 head.

 I was thinking that also, I have one assembled and running that won't go into 5th. I was thinking it would make a good turbo motor but I'm back to the F2 combo.

[MRieck]

The K7 also used the 24cc 392 head.

Yes...392 heads from mid 75 to 78 except for F2...all the same chamber volume.

[Don R]

 I've read here the F0/1 pistons can be used with a 300 head for a compression bump. I wouldn't lump all pistons as being the same even if they were assembled new under a 392 head. I remember Hondaman saying that he thought some 75 engines had various combinations of that year's pistons and heads just due to production changes and shortages at times.

[Don R]

 I'm wondering if the 392 heads used on later K and A motors got soft valve guides, meaning not all 392 heads are a good choice to use?

 I ordered a 100ML (CC) burette that should arrive today, I made a stand to hold it and hope to learn how to CC some chambers. I made a couple Lexan plates and a weight to hold them flat on the chamber.

[Don R]

 Wow, that 100cc burette is tall, my stand is too short. I'll need to get creative to keep it intact. I'm going to see if it will fit into a piece of PVC pipe and maybe hang on the wall where it's less likely to get broken.

[PeWe]

My K2 has "392" pistons. Cruzinimage +0.50mm. Higher compression.
Work fine. Total piston-bore clearance under 0.025mm.
It got a K7 cam too. Cheap in good shape.

I bought a 25ml burette. I seal the lexan plastic covers (with 2 holes) with a little oil or grease around the head's chamber.

My 392 head got new stock guides the shop cut shorter, reshaped the ends and cut another groove  to sink it deeper in the head.
The K valves keeper "waist" is very tall and shall not dip inside guide seal which a higher lifting cam will do.

I found a cheap head that looked good under the dirt. Most old heads I have found have bad guides. Maybe bad  too thin oil used?
A local shop close to me ported it. 33.5/28.5mm Kibblewhite valves. Sale on 28.5 exhaust valves

[Don R]

I have a set of Pontiac heads to check too so I got a big burette.
  The CB750 head of interest was on my friends stroker motor 1124cc, it had dropped sleeves and one sleeve/piston scored. It's been opened up for the bore, it needs milled, it was tightened down on an errant o ring.
  I did only drill one hole in the lexan, two makes more sense, thanks for that tip.
  I'm going to do the math for a turbo motor, I'd like to calculate an 836 10.25-1 piston with an F2 28cc head.

[scottly]

I've read here the F0/1 pistons can be used with a 300 head for a compression bump. I wouldn't lump all pistons as being the same even if they were assembled new under a 392 head.

The 392 K7 pistons I checked have a partial dome, worth about 2cc IIRC. Jerry's F0 pistons had a full dome, also IIRC?

[PeWe]

My K7 piston from Cruzinimage

[Don R]

 My local machine shop offered to hone a half mm, he can't bore anything that small however. That might return a cylinder to usable size if it wasn't worn too badly.

[MRieck]

My K2 has "392" pistons. Cruzinimage +0.50mm. Higher compression.
Work fine. Total piston-bore clearance under 0.025mm.
It got a K7 cam too. Cheap in good shape.

I bought a 25ml burette. I seal the lexan plastic covers (with 2 holes) with a little oil or grease around the head's chamber.

My 392 head got new stock guides the shop cut shorter, reshaped the ends and cut another groove  to sink it deeper in the head.
The K valves keeper "waist" is very tall and shall not dip inside guide seal which a higher lifting cam will do.

I found a cheap head that looked good under the dirt. Most old heads I have found have bad guides. Maybe bad  too thin oil used?
A local shop close to me ported it. 33.5/28.5mm Kibblewhite valves. Sale on 28.5 exhaust valves

The OS K/F valves have been discontinued from Kibblewhite for a while now. I do have some available but when they are gone that's it unless they will make custom valves.

[PeWe]

 33.5/28.5mm Kibblewhite valves. Sale on 28.5 exhaust valves

The OS K/F valves have been discontinued from Kibblewhite for a while now. I do have some available but when they are gone that's it unless they will make custom valves.

Is it 33.5 and 28.5mm valves you have?

I can find KW IN 33.5 and EX 28.5mm valves in Germany for 60€ each!!
A little bit high for spares just for sure.
Same price for a set of 4 would be different.

It is a pity that these kind of parts disappear.

APE has 33.5 and 29mm Ex in SS. Hard chromed stems OK in iron guides?

CycleX has 33.5 mm SS in. Not 28.5mm EX

I have 2 other ported heads with fresh guides and valves. One might be used in another build.

[Don R]

 Here's a fun toy. I tried to copy it with my numbers, but it came blank.

https://www.summitracing.com/popup/calcsandtools/compression-calculator

[PeWe]

I played with numbers.
I guessed about dome cc

[PeWe]

There is another way to calculate the compression ratio.
At which degree in valve close and measured compression added into a calculation .

The data I have is when  the  in valve closes at 1mm lift (ca 0.004").
This must be when it closes completely.

[Don R]

 Mike inquired about the 11-1, 71 mm pistons from Dynoman I'm getting and got 4.9cc for the dome top. I'm looking forward to this winters engine project.

[PeWe]

I think the 71.25mm piston I ordered from Dynoman on special order was later sold as 11:1 version. (22.5cc chambers as reference)

71.25 mm piston to the right. The flat outer area is 0.5 mm taller than the 70 mm piston to the left. Strange set of  JE pistons I got cheap that  forced a cylinder shave

Stock cylinder block (85.0mm) had to be milled 1mm at the top to reach 84mm height.
Billet block height with 71.25 mm piston is 84.50 mm.

My dilemma now is when to use my billet block. The K6 with 970cc runs to good to change.

The 71.25mm pistons are updated since last time.

[Don R]

 My big valve K2 RC heads measured 29cc. They were set-up for 72mm but need a trim to get them flat, a straight edge rocks a little between #3 and #4 chambers. As is, they would be around 9.6-1
 

[Tracksnblades1]

I think the 71.25mm piston I ordered from Dynoman on special order was later sold as 11:1 version. (22.5cc chambers as reference)

71.25 mm piston to the right. The flat outer area is 0.5 mm taller than the 70 mm piston to the left. Strange set of  JE pistons I got cheap that  forced a cylinder shave

Stock cylinder block (85.0mm) had to be milled 1mm at the top to reach 84mm height.
Billet block height with 71.25 mm piston is 84.50 mm.

My dilemma now is when to use my billet block. The K6 with 970cc runs to good to change.

The 71.25mm pistons are updated since last time.

No dilemma.. Build another bike..😁

Check that compression with a 70mm stroke and you’ll be using a F2 head..?

[PeWe]

I think the 71.25mm piston I ordered from Dynoman on special order was later sold as 11:1 version. (22.5cc chambers as reference)

71.25 mm piston to the right. The flat outer area is 0.5 mm taller than the 70 mm piston to the left. Strange set of  JE pistons I got cheap that  forced a cylinder shave

Stock cylinder block (85.0mm) had to be milled 1mm at the top to reach 84mm height.
Billet block height with 71.25 mm piston is 84.50 mm.

My dilemma now is when to use my billet block. The K6 with 970cc runs to good to change.

The 71.25mm pistons are updated since last time.

No dilemma.. Build another bike..

Check that compression with a 70mm stroke and you’ll be using a F2 head..?

I have another engine going on. Upper case milled for the billet block. No lightened and balanced crank. Only Super rods. Later undercut transmission with later clutch.
Final shaft is K2-K6 with later gear delivered with the transmission. I swapped gear and gave it new bearings.

The pistons work fine with 23.6/7 cc head. Thin RCS base gasket 0.001",  head gasket 0.003". My cheap compression tester must reach at least 210 PSI.

I have another K2 frame and most other parts. Need a swap with my running K2 which have a frame kit.
Carbs on the shelf are only 29mm.

My K6 has better handling though.

[PeWe]

My big valve K2 RC heads measured 29cc. They were set-up for 72mm but need a trim to get them flat, a straight edge rocks a little between #3 and #4 chambers. As is, they would be around 9.6-1

The RC pistons had all wide domes in need of opening the chambers, right?

My forged RC836 I bought 1983 to the K6 had such domes. Chambers over 24cc.
Even the older cast RC 836 with single oil ring had wider domes in need to widen the chambers a little.

Check head height. Stock is not less than 72mm, right? I measured an old K1 head to 72mm. It has got a light shave for good surface.

I let a shop shave off 0.5mm on a ported K2 head to reduce chambers width and volume. It must have been milled before, height is now 71mm. I have used it on the 970cc cylinder that is 84mm. Easier to get the cam chain on   At least 2mm off in total height.

[PeWe]

The calculator rounds up the displacement too much.
70mm pistons, 63mm stroke and 4 cylinders.
35x35 x π x 63x4. (Divide with 1000 to get the cc.)
This gives 969.8cc
NOT 972.95. (like Pi should be more than 3.15)

Pi as 3.1415926 is enough, easy to remember. Only 3.14 ends up in 0 .5cc less