Register Login
Save up to 15% with Adrian Flux insurance!
Reply
 
Thread Tools
Old 10-07-2018   #1
Join Date: Dec 2010
Location: Dartmoor, Devon
Posts: 324
Thanks: 5
Trader Rating: 0
United Kingdom 
Setting camwheel to TDC

What's the minimum safe valve head to piston cutout clearance, for a road engine?

I guess that would have to be at TDC plus the range of what? 5 degree crank of crank rotation either side of TDC?

It's easy to set the crank at TDC but as I haven't got a block/head on the bench to play with, can someone say if it's easy to also set the camwheel to its position corresponding to TDC? Block and head separated. Measuring distance perpendicular to deck, to
a) highest edge of valve above head deck, and
b) deepest point of valve cutout below block deck
and allowing for gasket thickness between.

They say that crank camwheel and head camwheel must be a matched pair - can someone explain why? Sure the two must be synchronised at TDC or mid stroke or wherever but doesn't the wheel-to-camshaft adjustability take care of that?
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides


Last edited by fostertom; 10-07-2018 at 11:59.
fostertom is offline Reply With Quote Quote 
Old 10-07-2018   #2
Join Date: Nov 2014
Location: suffolk
Posts: 454
Thanks: 15
Trader Rating: 0
United Kingdom 
Re: Setting camwheel to TDC

The matched pair stuff is to do with the different pitch crank and cam wheels. I also believe there are some with different numbers of teeth. They need to match otherwise the belt won't fit and/or your timing will be out.

What is your reason for wanting to know the minimum cut out required? The 8v fire is non interference so won't touch at any point (assuming standard specs of course)
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

dac69er is offline Reply With Quote Quote 
Old 11-07-2018   #3
Join Date: Dec 2010
Location: Dartmoor, Devon
Posts: 324
Thanks: 5
Trader Rating: 0
United Kingdom 
Re: Setting camwheel to TDC

Ah thanks - if it's only about number and pitch of teeth, and exact 2:1 diameters follow from that, that's easy.

There's no 8v in this job - it's an ex-1242 mk1 Punto 16v ELX85 head on a Punto Grande 1368 block.

That ex-1242 head is a near-identical casting to the Punto Grande head, same valve c/cs despite the 1242 block having equal bore c/cs but the Grande having different (irregular) bore c/cs. The Grande pistons have their cutouts offset, in order to match up with the valve c/cs of the head. And the valves heads are same diam, in the 1242 and the Grande. so the Grande cutouts are correct size, correct c/cs, to receive the valves.

That just leaves worrying about valve lift, and going from the 1242's 1.5mm thick composite gasket, to the preferred 0.5mm thick steel gasket of the Grande. I don't know but guess that both those factors taken together are going to reduce valve to piston clearance.

On a previous build we thought we'd checked it and test run v gd until suddenly valve contact - but I suspect wrong valve timing. Need to check it again properly now.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides


Last edited by fostertom; 11-07-2018 at 10:39.
fostertom is offline Reply With Quote Quote 
Old 11-07-2018   #4
Join Date: Nov 2014
Location: suffolk
Posts: 454
Thanks: 15
Trader Rating: 0
United Kingdom 
Re: Setting camwheel to TDC

i think the only way to be 100% sure is to assemble everything with some plastigauge or similar on the piston top. turn the cam by hand and see what indentations you have in the plastigauge to work out your clearances.


if you turn by hand then you shouldnt have any issues with damage.


i appreciate you said you havnt got a head to play with, but even with measuring using standard specs, this wouldnt account for a skimmed head or similar.
__________________
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

dac69er is offline Reply With Quote Quote 
Reply
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump
Similar Threads
Thread Thread Starter Forum Replies Last Post
(T) TDC sensor Hudson93 Cinquecento / Seicento 5 28-06-2013 16:55
when is tdc not tdc? dave Tech Talk 10 08-07-2012 21:57
(G) tdc? davidrainb Bravo / Brava 1 31-01-2008 09:09
(T) Bravo HGT 20v setting TDC fasteddie400 Bravo / Brava 5 14-10-2006 15:26
No 1 TDC - How do you tell??????? Anonymous FIAT Boo Archives 3 02-07-2005 19:11