Engine Compression Plates

General purpose topics/chat goes in here
StephenG80
Posts: 264
Joined: Sun Apr 30, 2017 10:42 pm
Location: ARGYLL UK

Engine Compression Plates

Post by StephenG80 »

Tried to google this to find out why they are fitted to some engines, when, purpose etc. . but there is not a lot out there. Can someone enlighten me? - I am just curious to know :ugeek:
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Engine Compression Plates

Post by Rob Harknett »

As far as I know they lower compression ratio to give improved fuel consumption. Fuel used needed to be saved in war time in particular.
StephenG80
Posts: 264
Joined: Sun Apr 30, 2017 10:42 pm
Location: ARGYLL UK

Re: Engine Compression Plates

Post by StephenG80 »

so were they something that was introduced during war time as a cheap alternative to changing machining for war time models and also so they could be retrofitted to existing machines? Also presumably to cope with poorer quality war time fuel?
zwarts
Posts: 514
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: Engine Compression Plates

Post by zwarts »

Stephen G80 wrote:so were they something that was introduced during war time as a cheap alternative to changing machining for war time models and also so they could be retrofitted to existing machines? Also presumably to cope with poorer quality war time fuel?
You have answered your own question in that last sentence, Stephen. The low quality fuel situation continued into the early/mid 1950's. This is why the compression plates were used from around 1940 to 1955 and less so after that.
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Engine Compression Plates

Post by SPRIDDLER »

Interesting letter/announcement/advice issued to owners by the Plumstead factory in Dec 1956 referring to fuel coupons/fuel economy........and referring to a chap who achieved 312.5 mpg with his 350 Matchless.

http://archives.jampot.dk/editorial/Roa ... e_1956.pdf
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
GOLDSTAR
Member
Posts: 2521
Joined: Thu Sep 11, 2003 1:00 am
Location: KENT UK

Re: Engine Compression Plates

Post by GOLDSTAR »

when I got my Velocette MSS many years ago the original purchaser told me he had the engine rebuilt by a well known Velocette specialist but because of the difficulty in obtaining a MSS piston at the time a Venom [higher compression] had to be fitted, in view of this and to restore the lower compression of the MSS a DECOMPRESSION!!! plate was fitted, why oh why are they always called compression plates is beyond me. kind regards
StephenG80
Posts: 264
Joined: Sun Apr 30, 2017 10:42 pm
Location: ARGYLL UK

Re: Engine Compression Plates

Post by StephenG80 »

thanks all - I have to agree Goldstar - if they were called decompression plates that would make a lot more sense :-)
zwarts
Posts: 514
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: Engine Compression Plates

Post by zwarts »

They are known as compression plates as their presence/absence determines the compression ratio of the engine. It's as simple as that!
User avatar
GOLDSTAR
Member
Posts: 2521
Joined: Thu Sep 11, 2003 1:00 am
Location: KENT UK

Re: Engine Compression Plates

Post by GOLDSTAR »

tommy rot! if one is not fitted then the compression is as per manufacturers figures when you fit a decompression plate you do exactly that lower the compression ratio therefore you decompress it. kind regardst
User avatar
vincentvv
Posts: 380
Joined: Sat Jun 21, 2014 1:17 pm
Location: Belgium

Re: Engine Compression Plates

Post by vincentvv »

Interesting!
Not fired is always a misser!
Locked