Rover V8 compression issues

General Chat About Engine Build

Moderator: phpBB2 - Administrators

Post Reply
Andrewrv8
Forum Contributor
Forum Contributor
Posts: 63
Joined: Sun Oct 19, 2014 7:55 pm
Location: Pembrokeshire

Rover V8 compression issues

Post by Andrewrv8 »

Can anyone throw any ideas past me on this one, basically, my rover p6 fitted with a 4.6 has been running quite rough and down on power and feels way off balance - chugging almost. I checked sparks - no problems there (megajolt fitted). So got the compression tester out :? results as follows:-
no 1 - 120psi
no 2 - 150
no.3 - 150
no 4 - 150
no 6 - 10
no 7 - 150
no 8 - 10
So, no 1 possible rings? but numbers 6 and 8 barely any compression at all which has got me thinking. Being neighbouring cylinders could it be one shared problem such as head gasket. The engine does not overheat or use water, neither does it use lots of oil - or blue smoke.
Could there be any other explanation such as incorrectly set lifter pre-load.
I would like to eliminate anything before taking heads off. Thanks in advance - Andrew


Triumph TR7 V8 3.9efi

garrycol
Knows His Stuff
Knows His Stuff
Posts: 527
Joined: Thu Jul 16, 2015 2:47 pm
Location: Australia

Post by garrycol »

The obvious thing is a blown head gasket between 6 and 8 - you wouldn't loose coolant and gases would not get into the coolant.

User avatar
Ian Anderson
Forum Contributor
Forum Contributor
Posts: 2396
Joined: Sun Nov 19, 2006 9:46 pm
Location: Edinburgh

Post by Ian Anderson »

Bolts holding rocker pedestal to n place come loose?

Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.

User avatar
ChrisJC
Top Dog
Top Dog
Posts: 5039
Joined: Mon Nov 20, 2006 1:13 pm
Location: Northants / Cambs
Contact:

Post by ChrisJC »

garrycol wrote:The obvious thing is a blown head gasket between 6 and 8 - you wouldn't loose coolant and gases would not get into the coolant.
Definitely.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

Andrewrv8
Forum Contributor
Forum Contributor
Posts: 63
Joined: Sun Oct 19, 2014 7:55 pm
Location: Pembrokeshire

Post by Andrewrv8 »

Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then :)
Triumph TR7 V8 3.9efi

User avatar
Darkspeed
Guru
Guru
Posts: 913
Joined: Sun Sep 02, 2007 4:43 pm
Location: Shropshire
Contact:

Post by Darkspeed »

Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then :)

Fingers crossed it's not a failure due to the support for the gasket dropping.
4.5L V8 Ginetta G27

Andrewrv8
Forum Contributor
Forum Contributor
Posts: 63
Joined: Sun Oct 19, 2014 7:55 pm
Location: Pembrokeshire

Post by Andrewrv8 »

Darkspeed wrote:
Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then :)

Fingers crossed it's not a failure due to the support for the gasket dropping.
I'm not quite with you there, on the deck face ?
Triumph TR7 V8 3.9efi

DaveEFI
Gold Member
Gold Member
Posts: 4603
Joined: Fri Feb 26, 2010 4:27 pm
Location: SW London, UK

Post by DaveEFI »

I've only once seen a gasket fail on an RV8 between two cylinders. That was on an early P5 high compression run on the cheapest petrol and pretty neglected, service wise. And it had damage to the block face.

I'm hoping you have more luck.
Dave
London SW
Rover SD1 VDP EFI
MegaSquirt2 V3
EDIS8
Tech Edge 2Y

User avatar
Darkspeed
Guru
Guru
Posts: 913
Joined: Sun Sep 02, 2007 4:43 pm
Location: Shropshire
Contact:

Post by Darkspeed »

If the liner was not fully seated at the factory its possible for them to drop in service The alloy previously supported by the liner can move inwards due to the pressure of the fire ring - The fire ring support is reduced and can then fail. Its rare.
Andrewrv8 wrote:
Darkspeed wrote:
Andrewrv8 wrote:Thanks for all replies, head gasket sounds likely then, I'll be in the garage tonight then :)

Fingers crossed it's not a failure due to the support for the gasket dropping.
I'm not quite with you there, on the deck face ?
4.5L V8 Ginetta G27

User avatar
ChrisJC
Top Dog
Top Dog
Posts: 5039
Joined: Mon Nov 20, 2006 1:13 pm
Location: Northants / Cambs
Contact:

Post by ChrisJC »

I dismantled a P38 engine last month that had a failed head gasket between 5 & 7.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

Andrewrv8
Forum Contributor
Forum Contributor
Posts: 63
Joined: Sun Oct 19, 2014 7:55 pm
Location: Pembrokeshire

Post by Andrewrv8 »

ok,head is off, and yes head gasket failure. Liners look OK so straightforward job I hope. This engine is definitely not neglected in any shape or form. My next dilemma, do I remove the other head and fit my stage 2 heads (supposedly destined for my tr7 v8!).
Thanks for the interest and replies.
Triumph TR7 V8 3.9efi

DEVONMAN
Top Dog
Top Dog
Posts: 1440
Joined: Sat Dec 13, 2008 2:46 pm
Location: Croydon UK

Post by DEVONMAN »

It might be worth checking the ignition timing. Incorrect timing can cause higher than normal cylinder pressures. Also check the head for flatness.
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!


Image

Andrewrv8
Forum Contributor
Forum Contributor
Posts: 63
Joined: Sun Oct 19, 2014 7:55 pm
Location: Pembrokeshire

Post by Andrewrv8 »

DEVONMAN wrote:It might be worth checking the ignition timing. Incorrect timing can cause higher than normal cylinder pressures. Also check the head for flatness.
I admit that I did have ignition timing issues prior to fitting the megajolt, but I checked true tdc at that time and I'm happy that it is now correct. It could've happened then to be honest.
I've yet to set the carb up properly - she is running quite rich. I have an AEM wideband fitted. This is the next task on the never ending list.
I will however check the head for straightness prior to refitting. Thank you.
Triumph TR7 V8 3.9efi

Post Reply

Return to “Engines Area”