Compression ratio

[davidd]

I would have thought with compression ratios that high the pinking noise would have told you something was wrong, but it is hard to argue with the math. Roy's is the quickest and cheapest solution. I would use an aluminum spacer. This can be sealed to the cases and I would think the O-ring would be happy with it. If you're worried use your favorite sealing compound without the O-ring. The compression plate will take some efficiency away from the squish band.

If you want to try and keep the squish band you could order a new set of pistons from Steve Hamel. You could specify them for the right compression and keep the squish. If you are certain about your methodology and conclusions, the first thing that you should do is disassemble and do the measurements accurately. This will allow you to decide what compression plate you need or what pistons you need.

I would think that you are correct about the difference in volume between the 500 and 600. I am not sure that they were the "wrong" heads, but they might have been the wrong pistons.

If I had a set of 600 heads I would swap you even!

Best of luck!

David

 

[Brian Thompson]

Hello Bill,
I have 3 pairs of TP's 600 cc cylinder heads. I believe they are from 3 different batches. I have a head off the first engine at the moment fitting valve springs to suit high lift cams. I have taken some photo's. I hope they help. I'll try to take better ones if needed. But I guess you really need to know the volume of the combustion chamber?
Let me know if I can help?
cheers
Brian

 

[Bill Cannon]

Mine measure 78cc so fluid just reaches the squish band, so it would be useful if you could measure it Brian.

For interest also a picture of piston top and TP split studs which make head removal easy with engine still in Egli frame.

 

[bmetcalf]

head removal easy with engine still in Egli frame.

I can see that in a Featherbed, but not an Egli ?

 

[Bill Cannon]

You just loosen swing arm spindle, release some cable ties then remove top bracket bolts and pivot the engine down until there is room to remove heads.

 

[timetraveller]

I also measured 78 ccs some years ago on one that I measured but did not put the details in with the earlier posting in case it was commercially sensitive.

 

[Brian Thompson]

Hello Bill,
Going on one milliliter is one cc
I managed to get 83 ml into the combustion area.
As seen here.
Sorry about the quality of the photo. But the oil is to the top of the combustion area.

 

[timetraveller]

I cannot see from the photograph but did you put a thin sheet of Perspex, or other transparent plastic, over the squish band? This has to have a very small nick in one place of its circumference to allow the final filling with oil and to let any air out. If not then the meniscus on top of the oil spoils the accuracy of the measurement.

 

[Brian Thompson]

Hello Timetraveller,
No I didn't go to that extreme as I don't have the equipment necessary. I assume Bill has done it similar to the way I have done it also.
So I hope this might help if possible.
Cheers
Brian

 

[Bill Cannon]

Hello Bill,
Going on one milliliter is one cc
I managed to get 83 ml into the combustion area.
As seen here.
Sorry about the quality of the photo. But the oil is to the top of the combustion area.View attachment 2832

Thanks for doing that Brian, it's much appreciated.
Given the extra 5cc you have found this would give total of 67cc installed with my pistons. This is still 10:1 and not the 9:1 I am looking for. So there is still something else going on!
Bill