[T2] (no subject)

[Robert Mann]

Mike Howe asked:

>replacing pistons and cylinders on type 4 1700.  Had to get AA piston set as
>this was only ones available. Old Pistons were dished.  New ones are flat
>top.  Distance from wrist pin to top of piston same on both types.
>
>Heads are in good shape from being redone recently.  Heads are flat in
>chamber area, no groove for cylinders.
>
>Question 1:
>I assume that my compression ratio will increase with this type of piston.

	That looks v likely.
	Also, any tendency to preignition (knocking) may be somewhat 
increased.  Hemispheric combustion chambers have usually been formed 
in the head, but many diesels and the excellent Rover 2000 engine 
have the hemisphere in a deeply-dished piston.  Shallow dishing is 
presumably a slight improvement to breathing which you now forego.


>Will it be enough to cause me problems?

	 One way to prevent all problems from raised CR is  -  wait 
for it  -  Water Injection as per 
<http://www.kuratrading.com/HTMLArticles/writings.htm>


>  Case is still split waiting on
>parts so I can't yet measure what compression ratio will be.

	Fortunately it doesn't matter, at least regarding 
preignition.  Just slap in water and CR up to 13:1 becomes OK on 
petrol.
	And plus you get: cooler exhaust valves, better economy, 
cleaner exhaust.
	Oh, and did I mention faster cruising?

>
>Question 2:
>Should I use the head gaskets that come with the gasket kit?  I have no
>groove in head to help seal and removing would seem to increase compression
>ratio as well.

	Given planar faces mating according to rigorous Chermanss 
enchineerink standards, no gasket is needed.  Yes, that gives CR 
slightly raised compared with that same engine plus head gasket.
	Almost-planar can sometimes be covered OK with beer-can aluminium.


-- 
Robt Mann
Whangaparaoa, New Zealand
'73 VW 1600dp Devon camper
'53 Meteor V8
various Jawa-CZ and Jawa-NZ strokers
http://www.kuratrading.com/HTMLArticles/writings.htm