Hiya all, my boyfriend has a sierra sapphire cosworth and it has no compression in Cylinders 1, 2, 3, but 4 has 60psi he has had a full head rebuild, brand new inlet valves, also a new headgasket & Also when the cams are removed the compression comes back on all 4 but was weak. As soon they go in its gone again etc please help he doesn't know what else to try!!

 

Firstly assuming the test is actually being performed correctly and with functioning tester...

If it has NO compression, then the valves are not closing.

For starters whoever rebuilt the head needs a bit of a slap, or certainly their work given a re-check.

Presumably he is doing a compression test because of other symptoms/problems too ?

It could be as simple as a lifter issue, or a complete and utter cock up with poorly installed valves.

 

Sounds like a timing problem , knowing this site you would of got a better response saying your single lol

 

Could possibly be the cams/timing belt not installed correctly.

If that's the case slap whoever fitted it lol comes back to same thing, valves not closing correctly.

 

Hiya guys thank you for your replies;

It was Impulse Developments that rebuilt it.

Also he has checked all the timing & cams and they're fine!

He just has absolutely no idea what to try next!!

 

has he taken it back to the company that rebuilt it?

 

Has it got hydraulic or mechanical lifters in it?
If its been change to mechanical then they could be gapped incorrect causing what you are saying
Failing that then it does sound like its not timed up correct

 

It's got hydraulic lifters

 

And no he didn't take it back to them as they was very blunt and rude! He asked them to sort it and they refused to take it back claiming the work was done perfectly !! We're just so confused!!

 

This engine needs dropping off with someone who knows what they are doing now im afraid. A high pressure leak down test will identify the problem area very quickly.

Testing it with no cams in doesnt really tell you much about the compression as the inlet valves dont open to allow any air in to be compressed, but at least all the low readings were the same which bodes well.

A possibility is the lifters are overpressurised for some reason so they are opening the valves when the cams are tightened down. Maybe wrong lifters installed?
Another worry is the fact it has had new inlet valves. I wonder if the valve sealing was tested when they were installed as ive seen bent / mishapen guides on a YB before after valve impact, and new valves wont fix that problem.

Finally, thinking out loud, there are YB cams out there with 2x woodruff keyways.
Is he CERTAIN the cam timing is correct? Were they set using markers (woodruff key problem wont be fixed) or timed with full lift (Woodruff key problem wont be an issue)

 

The only clear issue he can see is that the lifters are empty indicating that the oil is not getting up to them, however going to try and prime the oil pump and pressurise the engine, the valves were all replaced because impulse messed them up badly, the guy that done the second lot of work has built 50+ of these engines and runs his own company doing so, the valves won't hit the Pistons as I am lucky enough to have forged Pistons with valve cut outs machined into the crowns. Woodruft key wise they are singles and when stripped down pics were taken for reference etc and timing all marks are spot on!!

 

So this engine WASNT built by Impulse Developments?
Seems a bit of a confusing story...

Is this a 4wd engine? Was it long studded as part of the build?

Oil pressure can easily be built up without the engine running using a drill and adaptor in place of the distributor. Indeed it should be done before installing a YB engine to check all galleries recieve correct oil pressure.

 

Sorry my mistake! It was not BUILT by impulse the head was recondition to which they lied and didn't do half of the work they claimed to have done and still charged me £540 sent it to someone else who noticed 3 dead valve springs all hydraulic lifters were knackered he recut a brand new set of genuine inlet valves and pressure tested it to make sure everything was good without the cams in place it tested good pressure. The engine was rebuilt by himself with 2 other fully qualified mechanics helping everything was checked then double checked to make sure it was correct. It's a 205 2wd engine now have reverted back to standard head bolts and a reinz fibre gasket just to make sure it is sealing

 

Without being rude...if whoever rebuilt the engine is a "qualified" mechanic etc....then finding the problem really shouldnt be difficult when he has the engine/car in front of him.

But either way, the valves are not closing correctly that is blatantly obvious from symptoms described, and lifters not getting any oil wouldnt have any impact on that

Whether cams are not installed correctly, valve seats cut too deep, wrong length valves, wrong lifters etc etc
Again, all basic stuff that he can check although he may need to remove the head again.

But also stuff that should really have been checked before installing the head in the first place.

 

Tbh after reading all this the best thing I would suggest really is to either take the car to a specialist to get rectified, or if your partner is mechanically minded I would get him to take the head back off and get that checked by a specialist, as if you get too many monkeys playing about you could end up with more problems if the head work is poor

 

I can confirm this

I've just put a new newman cam in my saph, the new cam has 2 woodruff keys

 

Was this Impulse Developments in Rochdale? Seems a long way from Croydon.

 

TIMING MARKS?

If timed up like a pinto on the groove of the pulley this could cause compression problems. A YB tdc mark is the lug not the groove.

 

Note the lug arrowed and the groove to the right.

Paul