Late 80s Cosworth red top 2.0 litre - low compression - backfiring thru exhaust

[Jacques]

Compression of 100 in 2, 150 in 2.  Backfiring thru exhaust and carbs while adjusting timing.  Doing another compression test now.  Noted on-line that Edd China doesn't work on Cosworth heads, sends them to a machine shop.  While we continue trouble shooting, are head gaskets, etc., readily available  for these?  Being a Pinto block and popular in the UK, I would think they are still stocked.  Thoughts?  I'm sure we're going where many of you have been before us.

[MV8]

There are some special head gaskets that could be used to raise compression (multi-layer steel) or seal better (composition Group A gasket) but I would probably fit a standard Felpro for a pinto engine (after comparing to pics of the felpro). May want to put that off until you know what hard parts may need to be shipped to repair/rebuild the head. I'd pull the valve cover to look at the lobes, compare valve height at tdc (dropped seat?sticking open?) and look for a broken spring. You could also add a little oil to the low cylinder to see if it goes up a lot, indicating a bore/ring issue.

 

 

 

 

[Jacques]

MV8 - oil didn't affect the compression.  Thanks for the ideas about further steps.  This began as a re-timing exercise as I had removed the distributor.  We figure the timing is close but it is backfiring thru exhaust, etc.  Plugs are fouled now; want to replace them and see if it smooths out at all.  What plug would you suggest?  I have been running an NGK ZFR6F - 11.  it came with NGK BCP6ES.  Ideas?  thanks.

[Dave W]

Pull or loosen number one plug and turn the engine over by hand.  Should be able to hear the air coming out on the compression stroke. Set the crank pulley to the casted timing mark at 12*. Now verify that the rotor arm is pointing at number one on the distributor cap. You may want to mark number one location on the outside of the distributor body first. If the rotor does not align, pull the distributor [re-set] and try again without moving the crank.

[MV8]

I'd run either plug or the standard, colder BCP7ES plug with an .044" gap. It sounds like your firing order may be off. For the timing, if there are no timing marks other than tdc, I'd add a 10-12 degree btdc mark and adjust at warm idle to align with the pointer. If there is no 10btdc mark, measure the damper od, draw a circle on a piece of paper that od with a compass, make a mark to serve as tdc (doesn't matter where on the circle), use a protractor to find 10 or 12 degree cw from the tdc mark and mark that on the circle. Use the compass or dividers to set the distance. Place the compass/divider on the damper and mark it 10btdc (cw of the tdc mark). A black permanent marker works well enough or add a piece of masking tape along the damper for a contrast to the mark as a temporary reference. They make degree tapes for this but the damper od must be correct for the tape. Use a timing light to fine tune any static checks of the distributor rotor alignment.

[Croc]

 

I am going to assume you are referring to a 2L Cosworth YB engine.   Pinto bottom end and a trick Cosworth 4 valve head which was done for the FIA Group A homologation of the Sierra Cosworth RS/RS500.  Where it gets important is which variety of YB engine do you have?  They had the naturally aspirated plus monster turbo varieties.  Color of cam cover (i.e. red for you) is not always indicative as it was a dress up part from the Sierra homologation engines that could be bought separately.  The head could be standard or heavily opened out for better breathing.  A naturally aspirated YB could still be using the Group A gasket as it was heavily ported to breathe better.  These were a brilliant engine to exploring better breathing and it is amazing to think that at their peak in the late 80s Group A turbo era they were pumping out 650hp in a 2L 4 cylinder.  

 

I fully agree with @MV8 and @Dave W above on initial steps to eliminate timing/spark/combustion as a cause here as this is the easiest to rule out first.

 

Assuming you resolve that timing is not the issue then you are likely removing the head.  The YB weak point is always the head gasket.  These engines are normally pretty robust in the valve train.  I admit my initial reaction to your post was a breach of the head gasket between two of the cylinders.  These engines are notorious for eating head gaskets in high HP mode.  I keep spare ones of my engine for my YB Turbo WRC Escort.  Otherwise internally they are very strong engines. 

 

I would start my parts shopping with Burton Power UK here - give them a call as they are helpful to me on the phone:

https://www.burtonpower.com/catalogsearch/result/?q=cosworth+YB+head+gasket

 

Once you have your head off, as MV8 notes, try to match your old gasket to a new one in the Burton catalog. Consider sending a photo of it to Burton during your initial parts sourcing with measurements of the openings. I would definitely go for the best quality gasket you can get for this engine as cheaper is usually economy on an engine which treats gaskets as a consumable. 

 

When reassembling pay extra attention to the levelness of the aluminum head.  They are really susceptible to warping from even a minor overheat.