Board logo

Ford crossflow 1600 - low compression
Nickctp - 11/8/12 at 04:44 PM

Hi all,

I have recently been having a few problems with my engine in the locost. Upon further investigation this weekend - I am very down on compression (around 90) in 3 chambers and 120 in 4th. I have had a fuel starvation problem and recently discovered it was a fuel pipe blockage. Since it has been cleared I just can not balance the carbs and they are coughing and spluttering. The head gasket I think is fine - as are piston rings so I am left thinking it can only be the valves need re grinding due to lack of fuel etc? Does any one have any ideas/suggestions what to try or if you would guess the valves too?

Just need a little point in the right direction before I take the head off. I forgot to say - I have cleaned the carbs and checked the jets etc and no problems there! It's just the low compression and coughing and spluttering. I am running a 1700 cross flow on twin 40s, custom 4-2-1 manifold & 711m block.

Look forward to your response. Cheers guys

Nick

dray13dad - 11/8/12 at 04:50 PM

How about checking valve clearances, they maybe slightly tight if they are will not help with compression,if they are very tight would be a god clue to valve/seat problem maybe..

spiderman - 11/8/12 at 04:54 PM

Do a wet compression test to determine if it is valves or rings/bore. Put a little oil into the cylinder via the spark plug hole (about 15ml or a desert spoonful) and redo the compression test with all other plugs removed and throttle held wide open, if the pressure increases it is a bore/ring problem, if not then it is an upper cylinder problem. I suspect it may be valve seat regression if it is an upper cylinder problem and now would be a good time to have an unleaded head conversion.

johnemms - 11/8/12 at 04:59 PM

First get a carb balancer [ebay]CARBURETTOR CARB VACUUM GAUGE BALANCER 2 / 4 CYLINDER | eBay[/ebay]

When you have set the mixtures for maximum vac..
Set the indiviual carb air screws to balance the chokes..
Then balanced the twin carbs..
..
Repeat.. above..(assuming you have the correct jetting)..

Also check cam and apply correct advance for the cam you got..
ie BCF2 fast road cam - 16+ degrees static..

Then see where you are ....

Nickctp - 11/8/12 at 05:06 PM

quote:
Originally posted by johnemms
First get a carb balancer [ebay]CARBURETTOR CARB VACUUM GAUGE BALANCER 2 / 4 CYLINDER | eBay[/ebay]

When you have set the mixtures for maximum vac..
Set the indiviual carb air screws to balance the chokes..
Then balanced the twin carbs..
..
Repeat.. above..(assuming you have the correct jetting)..

Also check cam and apply correct advance for the cam you got..
ie BCF2 fast road cam - 16+ degrees static..

Then see where you are ....


Thanks for response, yep already have balancing tool - but just get them to match. 3 are similar and 1 is way out no matter what I do. (this is the 1 that I am getting a higher reading on the compression tester) so it all ties in really. Correct jetting too!

Will certainly check cam though

Nickctp - 11/8/12 at 05:08 PM

quote:
Originally posted by spiderman
Do a wet compression test to determine if it is valves or rings/bore. Put a little oil into the cylinder via the spark plug hole (about 15ml or a desert spoonful) and redo the compression test with all other plugs removed and throttle held wide open, if the pressure increases it is a bore/ring problem, if not then it is an upper cylinder problem. I suspect it may be valve seat regression if it is an upper cylinder problem and now would be a good time to have an unleaded head conversion.


Never thought of this - will definitely try before taking head off! ( already had the unleaded conversion)

Nick

steve m - 11/8/12 at 05:21 PM

Did you do the compression test with throttle fully open ?
as if you didnt, would explain the low readings,

also when my xflw had twin 40's on it, it would spit back if the timing was wrong

rusty nuts - 11/8/12 at 05:22 PM

As already suggested check and adjust the valve clearances before doing anything else, It's a good idea to check the valve lift as well as X flows have been known to eat camshafts which will affect compressions and cause spitting back through the carbs.Make sure you use the correct clearances for the cam you are using . Check that the auto advance in the distributor is working and also the dwell angle if using a points distributor , faulty points/timing / advance can cause problems . The last thing to do when tuning an engine is the carbs, if valve clearances/timing etc have a problem then you are wasting your time trying to adjust the carbs.
The suggestion of doing a wet test is good but due to the combustion chamber being in the piston on most X flow engines it isn't always successful ,anything more than about 10% increase on the compressions normally indicate faulty rings. A cylinder leakage test, also known as a leak down test is better.

britishtrident - 11/8/12 at 05:41 PM

You can make a cylinder leakdown tester fairly easily, loads of instructions on how do it out on the web but do a search on ebay for "leakage tester" you might just turn up a cheapy.

ianclark1275 - 11/8/12 at 11:33 PM

latex rubber glove on exhaust and carb mouth

put air line in spark plug hole...

at TDC for each cylinder

this can tell if there is a valve seat issue..

IC

steve m - 11/8/12 at 11:59 PM

Latex glove idea is pretty neat,

[Edited on 11/8/12 by steve m]

Nickctp - 12/8/12 at 10:16 AM

quote:
Originally posted by steve m
Did you do the compression test with throttle fully open ?
as if you didnt, would explain the low readings,

also when my xflw had twin 40's on it, it would spit back if the timing was wrong


Throttle was closed - I will re do today with it fully open. What should I expect though with it closed? Still seems very very low would you not agree?

cliftyhanger - 12/8/12 at 10:25 AM

Actual figues not too important as the gauges are never actually calibrated, but you are looking for them to be even and about right. One higher than the others is actually a bit odd too. So valve clearances would be my first port of call

steve m - 12/8/12 at 11:20 AM

my current xflow figures are the following, so i would imagine yours would be similar to the bottom figues
and as said anything with more than a 10 differrence will need investigation


1 2 3 4

shut 110 60 108 130 after engine build sept 2010

open 148 146 148 148 sept 2010

open 172 170 169 174 30 oct 2011


regrads

Steve

Nickctp - 13/8/12 at 07:53 PM

quote:
Originally posted by steve m
my current xflow figures are the following, so i would imagine yours would be similar to the bottom figues
and as said anything with more than a 10 differrence will need investigation


1 2 3 4

shut 110 60 108 130 after engine build sept 2010

open 148 146 148 148 sept 2010

open 172 170 169 174 30 oct 2011


regrads

Steve


Hi Steve,

Just finished another compression test with open throttle and I am getting vastly different results. 1 cylinder in particular I read 120 closed throttle and 220 open throttle!!!! There is a gradual difference though from cylinder 1 to 4. As follows with open throttle.

85 100 120 125

Doesn't bode well does it really. Still sounding like valves to you?

As I said vast difference between open and shut throttle and a difference between each 4 cylinders.

Cheers

Nick

Nickp - 13/8/12 at 08:11 PM

So what are the readings open then? You've stated that one is 220, but then listed them all closed again ( I presume?)

steve m - 13/8/12 at 08:16 PM

Ok,
I would back off the valve adjusting by a couple of turns, on each cylinder, and try again (easy to readjust)
wide /open throttle, and a couple of cranks on each stroke

if its still as per your figures, then investiagtion is needed

Steve

steve m - 13/8/12 at 08:17 PM

I would add, that if you have (120 closed throttle and 220 )
then i would suspect your gauge to be naff

britishtrident - 13/8/12 at 08:18 PM

Run the engine get it fully warm then do a compression test with all 4 plugs removed and the throttle wide open.

Nickctp - 13/8/12 at 08:19 PM

quote:
Originally posted by Nickp
So what are the readings open then? You've stated that one is 220, but then listed them all closed again ( I presume?)


My apologies nick - thanks for spotting that i missed off 100!! The open readings are as follows.

Open - 185 200 220 225

Closed are vastly different but as I said cylinder 3 for example 120!!


Nick

Nickctp - 13/8/12 at 08:20 PM

quote:
Originally posted by britishtrident
Run the engine get it fully warm then do a compression test with all 4 plugs removed and the throttle wide open.


Yep engine was warm and all plugs removed

Nickp - 13/8/12 at 08:22 PM

They will be vastly different, it's got very little air to compress when the throttles shut - hence the lower psi. Plenty of compression there fella, the imbalance could be down to valve clearances (some tight, some loose)

Nickctp - 13/8/12 at 08:22 PM

quote:
Originally posted by steve m
I would add, that if you have (120 closed throttle and 220 )
then i would suspect your gauge to be naff


As I thought - but tried a different tester from my neighbour and same result!! I put my readings down wrong to you- see my other post to nick! +100 sorry!!

Nickctp - 13/8/12 at 08:25 PM

quote:
Originally posted by Nickp
They will be vastly different, it's got very little air to compress when the throttles shut - hence the lower psi. Plenty of compression there fella, the imbalance could be down to valve clearances (some tight, some loose)


You think that could be causing the carb coughing and missing / assisting in running problems??

Nickp - 13/8/12 at 08:30 PM

quote:
Originally posted by Nickctp
quote:
Originally posted by Nickp
They will be vastly different, it's got very little air to compress when the throttles shut - hence the lower psi. Plenty of compression there fella, the imbalance could be down to valve clearances (some tight, some loose)


You think that could be causing the carb coughing and missing / assisting in running problems??


Could be, it won't help if you've got some tight clearances. If the valves aren't shutting properly it could be spitting through the inlet. I'd start with the low psi ones first

steve m - 13/8/12 at 08:35 PM

Nick ctp

If you can put your location in, as one of our extensive team in here, will be close, and can perhaps come round
if your close to RH11 im available!

steve

Nickctp - 13/8/12 at 08:42 PM

quote:
Originally posted by steve m
Nick ctp

If you can put your location in, as one of our extensive team in here, will be close, and can perhaps come round
if your close to RH11 im available!

steve


Done - not a million miles! Think I will whip the head off anyway can check the rings, bores too while I'm there. What you rek?

britishtrident - 13/8/12 at 08:52 PM

Testing with a closed throttle is pointless.

Nickctp - 13/8/12 at 08:54 PM

quote:
Originally posted by britishtrident
Testing with a closed throttle is pointless.


Done both mate - readings displayed are open throttle readings

rusty nuts - 14/8/12 at 07:28 PM

As I pointed out check the valve clearances and valve opening!!