15 replies to this topic

[psycho mini driver]

heres the situation.....need a new gear box, it burns oil and head gasket has gone, as well as i want to change the thermostat and housing. so my plan was to get a recon engine....but id rather not spend that much.
so i was thinking get a recon head which is built up already (as i would be replacing valves, guides and seals, as well as changing thermostat) and a recon box, fit it all myself and hopefully it will be ok!
but do you think the piston rings will be ok? as id leave the crank case alone. the car has only done 49k so im hopeing this will be the cheeper way.

[Rob]

have you checked the compresion? i once had an engine that broke a piston ring and it smoked like mad. if i remeber right it was 142 in the good bores and 121 in the one with knackerd rings. (it was a standard 998).

i was testing it with a gunsons compresion tester.

it had only done 54k.

[Guess-Works.com]

Just had a thought, and I may try this myself... but a compression test will only show if there's a leak, which could be Piston ring, Valve seats, headgasket or infact a crack...

By all means do the compression test, if there all equal(ish) then your likely to be ok, if you have one or two which are noticably lower or higher, than the others then there's a problem, normally with two ( if they are adjacent ) the head gasket has gone between the bores.

The thought is, at this point to determine rings vs valves vs anything else how about this... You can get these pressure adaptors connected to you compressor which allow you to change valve springs with the head in situe ( ie blow compressed air into the bore through the spark hole ) stick one of these on at a relatively high pressure and listen for the hiss, or use soapy water ??.....

Do you think it would work ???

[psycho mini driver]

the middle 2 cylinders seem slightly lower, so i assume the gasket has gone between these two. i guess i will have to do what i said, and hope the rings are ok. il either be spending out on the head etc and sorting it, or having to spend out on an engine, so mite as well do the cheep thing first.

guessworks, it sounds like a good idea. it may be hard to hear though.

[cowboy]

psycho, why are you getting a reconditioned head?

with low compresion between 2 & 3 it does sound like your headgasket has gone, you can check to see if teh leak is valve or rings, after you have done a compression test, add some oil to your cylinders and do another test, if the results are the same then, you need to grind your valves in again, if the results go up, then your rings are leaking....

the burning oil is lickelly to be valve guides you get new ones with a head gasket set.......

[dklawson]

Low compression in and of itself isn't necessarily bad. What is important for smooth running is the "spread" of the compression readings. Only check compression on a warm engine and be sure to spin the engine over until you get a steady gauge reading. Record the value for each cylinder and they should "probably" be within a spread of 10% of each other. If you find one cylinder WAY off from the others, it could be the result of bad rings or valves.

A more indicative test is performed with a "leak down tester". The device has two pressure gauges and an air regulator. The first gauge measures the output pressure of the regulator. Air leaving the regulator passes through a 1mm orifice to the second gauge and a hose terminating in a spark plug adapter. With this adapter screwed into the block (and the engine positioned so both valves for that cyl. are closed) you supply 100 psi air from the first regulator and record the pressure displayed on the second gauge. This gives you an indication of the AMOUNT of leakage. While performing this test you use a piece of tubing as a stethoscope to listen to 1) the carb body, 2) the exhaust pipe, and 3) the dip stick tube hole. Air heard coming out of the exhaust pipe indicates a leaky exhaust valve. Air heard in the carb indicates an intake valve leak. Air heard through the dip stick hole indicates worn rings/bores. I've forgotten what the magic (cut off) limit is for acceptable leakage. I'll have to look it up now!

Doing these tests or having them done prior to tearing the engine work done is a wise investment. If you decide to rebuild the head and find out the problem was always in the block... you've got a new head and STILL need to rebuild or replace the block.

[psycho mini driver]

well i need to replace the head gasket asap because i need my car, so i want it off the road for as little time as poss, if i do the head gasket, i mayaswell do the valves whilst its off, as they def need doing. buy the time i have baught the valves, seals etc iv already spent loads. plus i want to change the themostat housing. dont thing grinding them in will be enough as it is burnig a pint of fuel in under a week.if i grind them and it hasn't made that much of a difference then il need to do all that work again and spend as much again. plus iv had alot of little probs with the engine, so i would like to kno that its like new and working, then i can replase the rest at a later date.

[dklawson]

If you're in a hurry, and you've got money in the budget, you may want to consider installing a rebuilt head from a source like Mini Sport instead of taking the time to do the work yourself. This is not an option for us over here but could be an effective option for you. If you need to do more than the head... your car will let you know pretty quickly!

[Guess-Works.com]

Doug, like the sound of the leak down test, seems like a more scientific and tired method of looking for compression anomolies... Thought I was on to a winner then :sad:

But yes, as Doug says, if you got money to spend then get another head and do a swap, or even better a Known to be good head from reliable sources

[dklawson]

I looked up the numbers for leak down testing.

Each brand of leak down tester will have its own instructions and you should follow them. (by the way, you can easily build one yourself). Keep in mind that if you supply the leak down tester with 100 psi air from the regulator, the difference between the two gauges indicates directly the percent of air leaking out of the engine. (i.e., If gauge one (regulator output) shows 100 psi and gauge two (between the 1mm orifice and the spark plug adapter) shows 70 psi, you have 30% leakage).

A new or really good engine will have less than 10% leakage. A good engine with some hours on it will have 10-20% leakage. One with 20-30% leakage is in need of repair. If you have more than 30% leakage it's likely you have something seriously wrong requiring immediate attention.

I left out one other place to look for the leakage. In addition to listening to the tail pipe, carb, and dip stick hole... remove the radiator cap and look for bubbles. Air coming out there will indicate a blown head gasket.

[psycho mini driver]

ok, im not sure now if the head gasket is gone. the water is going frothy and it had gone down alot the other day. it goes especially frothy when the car is reved. is there anything else it could be apart from the head gasket?

[Guess-Works.com]

pretty sure sign. When you change the Head Gasket, use a good quality one, I now only use a Payen BK450.

[psycho mini driver]

what other signs should i be looking for to know for sure??

[dklawson]

What symptoms you see with a blown head gasket depends on a lot of variables. The symptoms you see depend on whether oil is leaking into water, water into oil, or combustion gasses into oil or water.

Blown head gaskets can create: oil mixed with radiator fluid, radiator fluid in the engine oil, bubbles blowing through the radiator, clouds of white smoke following your car, a dip stick that's blown out of the block... it just depends.

[miniman5]

from what ive read then it sounds like the heads gone especialy as the coolant needs topping up. why do u want a new thermostat housing??