10 replies to this topic

[Pigeonto]

Ok, I'd like to know a bit more about what this test can show. I'm unhappy with the new engine I have fitted and now covered 500 miles with. The oh so common puff of white smoke on start up has reared its ugly head again and I'm pretty sure its using its fair share of oil.I carried out the test and the result was very good according to all sources,in that they were all exactly the same and at 20%. Now what I'm wondering is this. Can I assume that if not much compression is going down,is not much oil capable of coming up?? I only fitted valve stem seals on the inlets and will now fit the exhausts but I dont hold out alot of hope it's going to help matters.Its going down to Goodwood on thursday-some 100 miles- and I'm not going to be holding back on the journey just in case its needs a good blast.Not that I poodled about much during these 1st 500 miles but I'm concerned now that it has glazed the bores. What do you think if you have done some leak down testing and know about it.

[bmcecosse]

How 'new' is the new engine? What was done to it - and by whom??

[Pigeonto]

Yes,sorry,good point.Total job:- Rebored +.060.Crank grind,cam bearings and billet cam 276,new followers, refurbed head with all new valves 35.6 / 31.not that the spec makes any difference,I suspect you mean re-ringed or re-bored. All done very precisely,ring gaps checked,piston to bore clearance spot on as recommended.I built it.Wasnt brave enough to use just WD40 on the rings so I used oil but with WD added to thin it.I know this area is a hot potato but am pretty sure the factory would have oiled them. I left the (AAA) needles as per the 1275 that it was before going to 1330 assuming that being as they were ok before,adding another 55cc they would be hopfully a bit weak to help with running in. I'm taking it for a mixture test tomorrow on the RR to check fuel mix at all running conditions in case its too rich....sincerely hope not

[dklawson]

My engine is also at about 20% which is a bit high for a freshly rebuilt or low mileage engine. Ideally it would be below 10%. In my engine's case I blame the ring gap which was wider than desired. I did not alter the ring gap... they were just wide right out of the box. I sent K. Calver an email about the gap before finishing the rebuild. He told me that since I was building a street engine I should not worry about the ring gaps I measured. So far he has been right. The engine runs like a top even with the leakage at 20%

Perform your leak down test again and if you did not do this before, take a length of tubing and hold one end to your ear, the other end to various points around the engine/car. If you remove the oil filler cap and hear leakage into the block/head then you have ring blow by (which is what my engine has). If you hear an undo amount in the intake or exhaust you have a valve problem. It is unlikely you have a water jacket or head gasket issue with such a new rebuild but removing the radiator cap and watching for bubbles during the leak down test will quickly show if that is happening.

[bmcecosse]

Does sound like a good rebuild - I think you need to run it in carefully for a good few more miles !

[Pigeonto]

There's me trying to make it look like the engine may have been built by someone who knows what he's doing and I didnt even mention new oil pump....... don't worry, it's in there.Along with re-sized conrods down to bottom factory size and then I insisted upon him NOT just opening up his bible to find out what size the crankpins are originally and willy nilly subtracting 10thou.No.I made him measure the assembled rods with the new - .010 shells fited. We then agreed on a one thou. running clearance and the crank was reground to that size( I think it resulted in only removing 8.5 thou.)Primary gear to minimum factory end float and running clearance.Intermediate gear end to minimum factory end float.Crank end float too. Pretty much blueprinted it.This is why I said it was done precisely and also why I'm pretty peeved if it's glazed after all that time trouble and expense.

[Pigeonto]

Unfortunately this doesnt appear to be a subject about which many of us are too familiar,but it seems that I'll be pulling it down and glaze busting/re-honing anyway because I did the 1st oil change today and only 4pts came out so it's used 4 pts in 500 miles!!

[ACDodd]

Bore wash I would suspect. measure the bores and see how muchwear you have, 20% After 500miles is a bit high. I would expext 10 to 15% on a road engine. Although to be fair I do not know what test pressure your leak tester is using.
Very familiar with leak testing here.

AC

[bmcecosse]

Is it running rich? What colour are the plugs ?

[ACDodd]

As a guide MLM use 20% as a benchmark for remedial work. ie if the leakage is 20% or more work is needed as a measurable difference in power will be produced by reducing this. the biggest cause of cylinder leakage on the A-series is valve seal.

AC

[Pigeonto]

Out it comes then. This can all get very confusing/conflicting.I have read such expressions as "no oil of any description should go anywhere near these surfaces"(bore and rings) from Des Hammill when suggesting that WD 40 be used for assembling the engine.My rebore man"dip the pistons and rings in oil before puting them in" If bore wash is the culprit then clearly we DO need oil on our rings. Dunno. BMC, to answer your question,the plugs are perfect fawn colour BUT it always smells rich from exhaust which is sooty.I attributed this to valve overlap from the 276 cam but now I dont know. What i HAVE done is asked the local Rolling Road people to run it up and test the mixture under all conditions,accelerating,decelerating,cruising and idle so that I know.If I am to re-do it all,I cant have any doubts lingering as to bore wash or not.