Well where do i start?

[johnd]

Hi all,
need some help with my rr p38 v8. I have just rebuilt the engine and finally got it running today only to find that it is running on 7 cylinders.

i have scanned it with my snap on diag tool and it said injector 3 was knackered so changed it.
Done a compression test and i have low compression. Does anyone have any ideas or will i have to start stripping it down again.

cheers
john

 

[rewmer]

Do you have low compression on just the one cylinder or all ? When you re-built did you re-con the heads ? You may have a leaky valve. How far did you go with the re-build ?

 

[johnd]

Yes i skimmed the heads changed a couple valves and seals, big ends, crank, block (from my old rr but was in top condition) complete gasket set, transfer box, thermostat, water pump, spark plugs and leads and probably more that i cant remember off hand.
cylinder 3 is really low but the others are ok.

My mechanic is trying to blame it on a piston ring as this would have been in my block hence nothing to do with his work but the block was working very well when removed.
Are there any checks i can do?

cheers
john

 

[Sean]

My mechanic is trying to blame it on a piston ring as this would have been in my block hence nothing to do with his work but the block was working very well when removed.

he's probably right - did you do any comp tests before starting the rebuild

 

[johnd]

no i didnt do a comp test on the block before putting it in.
I done a comp test on the engine before the rebuild but had 3 cylinders with little or no compression.

 

[Sean]

no i didnt do a comp test on the block before putting it in.
I done a comp test on the engine before the rebuild but had 3 cylinders with little or no compression.

you didnt do the rings and your supprised that there's still a compression issue ?

 

[johnd]

The engine was running fine that is the only reason i used the block from that engine. The mechanic didnt recommend i change the rings he just asked if the block was running before. Im not very mechanically minded which is why i paid for the job to be done, he also said that if its a ring it MAY just start working again.

Is there no definative way of checking what the problem is without taking the engine to bits again?

 

[Sean]

Is there no definative way of checking what the problem is without taking the engine to bits again?

not really - a few mill of oil down the bore of the offending cyl just before you do the comp test will help show if it is the rings

 

[rewmer]

I have to say I am surprised your man has gone to all that effort, and not at least checked the rings when it was appart. I would have expected at least to have mic`d the bores to check they were in tolerance. If he did the big ends, how hard would it have bean to pull the piston out? Low compression means you have air escaping somewhere, either past the rings as mentioned or past one or both of the valves, or even the gasket. Are you sure the heads where skimmed?. As suggested a squirt of oil down the bore will soon tell if the rings are suspect. If this doesnt improve your readng then I would look to the valves, but I would hope they where all at least re-lapped in the re-build. Looks to me as if you still have some work to do.

 

[johnd]

The heads were done as i took them and picked them up afterwards. if it were a gasket would all cylinders not be low? Is there anyway to check the gasket?

 

[rewmer]

If the heads where skimmed, then its unlikely to be the gasket. My money is on the rings, either worn or stuck. If they are worn they wont get better, if they are stuck then there is a slight hane on them freeing off , but I wouldnt count on it. You make have to just bite the bullet and get back in there. Head off sump off and pull the piston. But if you go that far - do them all....

 

[rewmer]

If the heads where skimmed I would doubt very much it is the gasket. Do the trick with the oil in the bore and go from there. On a personal note, try and keep your chin up, it is a mechanical thing that can be fixed, its just a shame that its not quite right yet.

 

[Sean]

and when you've managed to pick yer chin up orf the floor go have a moan at whoever did the "rebuild" cos they should have done the rings as well

 

[johnd]

I suppose its not all bad cos i held back £500 which was going to be paid on tuesday when i pick up my bmw from him so if he dont want to sort something out for me i wont pay him.
Should i change the pistons as well?

 

[bwarb]

I suppose its not all bad cos i held back £500 which was going to be paid on tuesday when i pick up my bmw from him so if he dont want to sort something out for me i wont pay him.
Should i change the pistons as well?

Unless there are signs of physical damage and/or wear on the lower "thrust" faces of the pistons (easily checked with a mic), then I can see no real reason to change them.

Of course, if you decide to rebore the engine, oversized pistions will be needed so they will have to be changed ......

 

[Sean]

just outta curiosity how much has he charged you for this rebuild ?

 

[johnd]

Well £1600 to do the job and including all parts except for the block, and including skimming the heads, spark plugs and leads, remove and replace the transfer box(not including the box), air flow meter, a "solenoid on the transmission and 1 injector.

does this sound too much??
i thought it was quite reasonable.

 

[Sean]

for that sort of money you should have got a complete, high quality rebuild along with a 12 month warrenty - they should also have bench run it before giving you it back