told rebuilding head with 275k miles, not a good idea. HELP

[clydesdale]

I did not take the head off yet on my 325is with m20. I have been eating a spark plug or 2 every 10-15k miles. I have a little oil in the coolant and was thinking of having the head done. I called a few specialists and one suggested not to bother and that I would likely cause more problems like blowby and oil consumption. They suggested just leaving it alone and start looking for a new motor. What do you think. With 275 thousand miles, would you bother with a valve job and surfacing the head or just finish the timing belt and leave that damn car alone?

[beemerbird]

At over 200K, I had the head checked over in my old '86 325i and the guy who did it said it looked like it hadn't been out of the showroom, virtually. These engines were built for high mileage, remember.

[clydesdale]

It is the bottom end that I am worried about. The guy I spoke with says that these motors often start consuming oil and have blowby because the bottom can't handle the compression that the new head provides.

[Kieran_n22]

Bollox! Get the head pressure tested and if its ok get it fixed

[Gwynleym10]

Do they realise it is a BMW engine? (I see you are in the US)

[Jim320i]

Did he also offer you a price to take the car out of your hands?

[German-Whips]

At over 200K, I had the head checked over in my old '86 325i and the guy who did it said it looked like it hadn't been out of the showroom, virtually. These engines were built for high mileage, remember.

Spot on. If the engine has been well cared for and regularly serviced and maintained well there shouldn't be a problem. Consumable parts and other parts which can be worn out due to fatigue and cyclic loading may be wearing out, but in general a well cared to engine should be able to withstand the mechanical work done.

Having said that, my 56k mile engine in my daily runner hasn't been maintained properly and has got a lot of issues with it! Bearing in mind it is a french car of course

[clydesdale]

What would pressure checking the head do? If there is a crack in the head, I hear it can be fixed and I would get a resurfacing and a valve job. The head will end up being fine. But, the bottom end is tired and may not handle the compression well and consume oil and have increase blowby. I called turner motor sports in MA, USA and they referred me to a place in Western USA, who are bmw specialist machine shop.

[gooner1]

Hi fella, as someone who is attempting to rebuild a 325i engine at the moment
maybe I can help out a little. If you decide to go ahead with the head work, it would be crazy
not to freshen up the bottom end a bit. Piston rings, Seals, Gaskets, Oil pump strip and check at the least. Check the Honing in your cylinder bores and generally have a good look at everything.

Post up pics of the parts you remove and someone here will give you sound advice.
Be warned though, it all adds up $wise. Then again you will have an Engine that's good enough
for another 275 thousand miles. Or take a chance on buying a used engine and all it's possible faults.

Good luck either way.

[e301988325i]

If it's not using oil now, there's no reason to suspect it would after having the head done, however a lower mileage engine swap may be a cheaper option, but there's no guarantee a lower mileage engine is in better condition if it hasn't been serviced properly and yours has.

[daimlerman]

After 275k miles,even your little USA miles,it could do with a bit of love and cash!

[clydesdale]

Yeah, I think I am looking for an ugly 325i four door with rust, but a low mileage m20. It is either that or change out to a 24v dohc. But, that may spoil the low stress simplicity of my e30. Btw, if I just slap the timing belt on and leave the head on the car, would you bother with attempting to change out the nasty front crank seal. It requires a quart of oil every 900 miles.

[gooner1]

Probably me but i'm getting confused. Is your Oil usage/ loss due to seepage from the crank seal
or is it being burnt up in the engine. Is your car emitting smoke at all and what do you mean by
" eating a spark plug or 2 every 10-15k miles."

I'm not the person to solve your problems but a clear, full description of what's happening
will help those that can.

[B7]

Probably me but i'm getting confused. Is your Oil usage/ loss due to seepage from the crank seal
or is it being burnt up in the engine. Is your car emitting smoke at all and what do you mean by
" eating a spark plug or 2 every 10-15k miles."

I'm not the person to solve your problems but a clear, full description of what's happening
will help those that can.

This especially on that milage.^^^

If the bottom end has any weaknesses (which is likely in this case), rebuilding the head and refitting it to the same bottom end will seal its fate. The reason is that by re seating the valves, new gasket and a light skim, your are giving it back it's full compression again. I'ts fine on most engines but remember this thing has nearly 300k on it!!!!

My old 2.5 in the convertible did the same. I built the head as it had burnt a valve or two out due to the Valve stem oil seals being shot. I fitted the new head and within a couple of thousand miles, it started using oil and smoking.

If it's burning plugs out, it's running hot. I suspect it's well carboned up by shot Valve Stem Seals letting oil down the stems and leaving carbon deposits when it fires. This carbon then glows hot when it's running and so the engine runs hotter.

Add that to slight oil in the water? It's time for a major freshen up IMO.

You say slight water in the oil? These engines rarely blow the head gaskets as people think. They have much more tenency to crack the head. You therefore get no overheating, no steam from the exhaust, no pressurisation of the cooling system andnothing will be detected by any sniffer test. All you get at the beginning is slight oil contamination in the coolant where it's being forced into the Camshaft chamber area. The crack will be under the cam somewhere normally at the rear above either 4 5 or 6 (as thats where the M20 runs hotter). Sometimes you can remove the cam cover and see nothing as either the crack is in the cam bearing surface (See Simon13's thread on his red 2 door 325i) or it's so minute it's hard to see. Only a pressure test of the casting will show it.

Hope this helps and let us know the result.

[clydesdale]

B7, you basically described what the 2 engine builders told me. The last guy I spoke with was right in my town, so I no longer need to find a guy to build the head. He has been building heads for dealerships and independent shops for 20 years. But, he told me not to do it for exactly the reason you described.
My first warning was that the car started missing and was down a cylinder. I pulled the plug and saw that the spark plug insulator had cracked off. I put a new plug in and the car drove great. I then had the same issue return about 10 thousand miles later. I replaced the plug and that was over 10 thousand miles ago and it is still running great. But, I am due for a timing belt. So, I decided to dig into it and when I drained the coolant, I noticed that it was a little darker. I do have to add coolant at around every 3 thousand miles or so. I thought I would address the head gasket, which is what I thought was wrong with the car, while at had it apart. But, after talking to several people in 5 different states in the US, I came across 2 reputable builders who described exactly what you just described.
My question for you is, under the above scenario, am I likely getting coolant into my oil as well? Is the oil being contaminated or just the coolant? Thanks

[B7]

Depends on how bad the crack is and by the sounds of it, if yours has cracked, then no, i'd not expect to see any coolant in the oil.

The reason is that the coolant system pressure is far greater than crankcase pressure. Therefore the coolant is forced out through the crack under pressue rather than oil forced into the water galleries.

The fact that you only add coolant every 3k and it's been like that for 10k, says to me the head gasket is actually still good. Over that kind of mileage, I would have expected it to have blown it's lot by now.

However, you say the coolant was darker? With oil in the coolant, it would either emulsify (a look akin to mayo) or there would at least be oily residue at the water level in the exspansion bottle as oil and water don't mix? So having said all of the above, I'm not convinced the water loss is into the engine in anyway. Adding coolant every 3k could be something as little as a small water leak, maybe pump, throttle body, outlet hose at the back of the head?

[clydesdale]

What would then cause the cylinders to eat my spark plugs? I am going to do a compression test today. What numbers should I expect with 275k. I thank you greatly for your help.

[Brianmoooore]

The reason is that the coolant system pressure is far greater than crankcase pressure. Therefore the coolant is forced out through the crack under pressue rather than oil forced into the water galleries.

This is true most of the time, but there's a period before pressure has built up in the cooling system, and when everything is cooling down after the engine is stopped, when the situation is reversed, so there's usually some contamination of the coolant as well.
As already said somewhere above, the spark plug problem is likely to be related to carbon in the cylinder head, and the bore/rings in question are unlikely to have escaped damage from the broken ceramic.
Expect scores in the bore wall, and ring gaps in excess of those on the other pistons.

[clydesdale]

The compression numbers are in. I am labeling the cylinder 1-6 starting with the front of the motor, radiator end.
1 170
2 170
3 170
4 170
5 100-150- This cylinder varied and did not have consistent hits on the guage
6 180


Sooooo, what is possibly a happening on the 5 cylinder?

[gooner1]

Piston rings

Try the test below.

Confirm you have a bad piston ring by squirting a moderate amount of 10w30 motor oil in any piston with a low compression reading. If the compression improves after this, it means your piston rings absolutely need to be replaced.

Read more: How to Test Car Piston Rings | eHow.com http://www.ehow.com/how_4486238_test-ca ... z1Pf2VjctP

[B7]

The compression numbers are in. I am labeling the cylinder 1-6 starting with the front of the motor, radiator end.
1 170
2 170
3 170
4 170
5 100-150- This cylinder varied and did not have consistent hits on the guage
6 180


Sooooo, what is possibly a happening on the 5 cylinder?

Theres a problem with no.5 without a doubt. Head needs pulling. I'd say the exhaust valve has burnt out and it occasionally does not seat properly. If it was rings I think it'd be more consistant.

As Brian says above though, if a plug broke up, where did the bits go???? The reason it broke up was due to hot running due to carbon build up I reckon .

Was it No.5 that broke up?

[clydesdale]

Ok I added oil and got 210 on the previous 170 cylinders and about 220 or so on the 180. The cylinder in question only bumped up to 170. But, here is the real question:
Why are the hits inconsistent on cylinder 5. The motor will turn 2-3 times and not get any reaction on the compression guage. Then it will bump up and couple of times and then may go a cycle or two with no reaction.
I was cycling the motor for 5-6 pulses on the guage. The other cylinders all hit the gauge consistently, #5 would sit out a couple of cranks with no reaction, even with the oil.

I think it was 5 that broke the plug. But, why did it break a plug. But, there were chewed up insulators on atleast one other plug at one time. So, it wasn't the same cylinder each time.

What is the deal with the cranks that do not react on the compression guage and probably most importantly, what can I do with this engine? I am going to leave the head on and put it all back together and keep on driving it. I am going to keep my eye out for a donor motor or a nicer e30 and take off the parts I like on my car. How long can I keep whipping this horse? It drove fine before I took it apart.

[B7]

Without taking the head off, it's impossible to say why the irratic readings on No.5 occur.

I did have one thought though. If a peice of insulator is in there, mabe it's jamming a vlave occasionally? hence some times it gets no compression reading, then if it dislodges again, the valve reseats?

Its a long shot but please let us know what you find.

[DanThe]

Find a decent engine to rebuild and weigh your scrap

[retroboyo]