Technical 500 head on 600cc cylinders question

[jjacob]

Still working through my options here in the USA. Supply of 126 engines on this continent is just about dried up and I have not been able to find any 126 transmissions in North America. I am still investigating importing engines ($$$), modifying my 110F, etc.

One option is to modify my current 110F engine. I would bore block to accept 600cc cylinders/pistons (I think 650cc might be too much?).

Questions about using my current 500 head on the 600cc cylinders.

1. Since the combustion chamber on the 500 head is smaller, would this not favorably increase my compression ratio and eliminate the need for reducing the thickness of the head? Looking to try to get to 8.5 to 9.0 to 1 ratio with the 600cc displacement.

2. What would be the largest intake valve that could be fitted to the 500 head without compromising the structual integrity of the head? I would leave the exhaust stock at 28mm. Can a 33 - 34mm valve be used (32mm is standard?)? Is there enough room?

After this Friday I should have enough information on my engine options and will post those options on my other thread discussing engine transmission options for comment.

Thanks,
John

 

[Bambino]

2. What would be the largest intake valve that could be fitted to the 500 head without compromising the structual integrity of the head? I would leave the exhaust stock at 28mm. Can a 33 - 34mm valve be used (32mm is standard?)? Is there enough room?

John,

It might be best to take your 500 head to a trusted mechanic and get his advice. An increase to 33mm will give you 6.3% more annular space whereas 34mm will give you about 13% more.

You are right about the exhaust valve - there is no need to increase its size.

Chris

 

[Toshi 975]

I am running a 500 head on 652ccs barrels on a bored out 500D crankcase. Head is ported, 34mms inlet valves but not skimmed. I recently bought another 500 crancase that had been fitted with 594ccs barrels. Long story but turned out that the machine shop had part bored the casting then put a step on the base of the barrel location base. The idea was to give a little more surface area on the location faces on the crankcase where the required 10mm spacers sit down under the barrels. I never used it in the end as I already had the other crankcase in being bored out so I still have the bare part bored one with the spacer rings if anyone is interested in building a "hot" engine.
Going back to my 652 / 500 engine , it is running very sweetly but only done about 40 miles so far but it is looking good and lots of vroom !

 

[jjacob]

Toshi,

Can you post some pictures of the 594cc block machining work? I am having a little trouble visualizing it. They machined a pocket for the spacer to fully sit in?

John

 

[Toshi 975]

Hi John,
ever since my computer had a nervious breakdown and I had to rebirth it I have had real problems trying to post pictures. I will try & explain it a bit better. The machine shop took a skim off the holes in the crankcase but not to the extent that the 594 barrels would fit. Then they took a skim off the base of the barrels to fit the crankcase but left the top 10mms as standard and made 10mms spacer rings to suit. For some reason the owner then decided to use a 594 500R crancase instead. He swopped over the barrels which would still fit OK as the top 10mms of the location part was still standard size. .