Compression results - Worth Rebuiding?

[me61ic]

Hi again, as said in my previous post, I am performing a ground up restoration in my AH BJ7. Right before starting to dismantle the car I did a 1000km trip with it, and I had to add around 1liter of engine oil during the trip. Now that I will be taking the engine out of the car I was wondering if it is worth to redo the valves (and also prepare them for unleaded fuel), or while I am at it, to also replace the piston rings. I have done a dry compression test and the results have been as follows:

1st cylinder: 125 PSI
2nd cylinder: 130 PSI
3rd cylinder: 125 PSI
4th cylinder: 125 PSI
5th cylinder: 130 PSI
6th cylinder: 125 PSI




What would you guys do if you were me?

 

[Bob_Spidell]

My answer is a question: why NOT rebuild the engine, since it will be out of the car? Yes, do the unleaded head mods, and whatever else is needed. Hopefully, you can get by with just a light hone of the cylinders, but if they're scored then a re-bore--and new pistons--are in order (broken rings are not uncommon). I've heard--have yet to do it myself--that Healey engines benefit from some mild head work--port matching mostly; no need to hog out the ports.

Before you pull the engine, do a 'leak down' compression test. That should tell you whether the somewhat low compression is due to valve or ring leakage--if it's valves you could consider just doing the head work, but your somewhat high oil consumption is most likely due to ring wear. How is the oil pressure?

 

[RAC68]

Although I do agree with Bob that a look to see the condition of pistons and cylinder walls should be done, let me caution you that once you start to address one section of the engine, you will be drawn to all others. If your cylinders are not scored, do you not check for roundness and replace the rings? If you put new rings in, should you not replace the rod bearing at the same time? The point is you either decide to rebuild the engine or don’t and a good rebuild will not be cheap or simplistic.

However, that being said, you can address specific isolatable sections of the engine for specific conditions. The valve train can be isolated and addressed for excessive oil leaks, the timing chain and tensioner for being stretched, and the installation of a rear oil seal can be performed without entering into a full rebuild. But, don’t expect limiting yourself to stay behind the line will be easy, especially with your Vision of your total redo in your mind.

Since your compression numbers seem respectable and with no presented issues on your 1000Km road trip, it sounds to me that your base-line issue comes down to available funds. If you have the available funds at this time then a full rebuild is both reasonable and opportunistic with the engine already coming out of the car. Without excess funds, then addressing the obvious components is reasonable. These engines have, and will, last quite long and I presume you will not be using your car to commute 100 miles one way to work each day.

Either way you decide, I suggest you develop a cost projection for a full engine rebuild that includes both replacement parts and services. This exercise will give you a clear cost and time estimate, including trade-offs and recommendations, and allow you to put clarity to a real decision.

Good luck,
Ray (64BJ8P1)

 

[bob hughes]

RAC68 is right, you will be drawn in. My engine was burning oil at the rate of less than 100 miles to the pint, I have started the process of rebuilding the engine, - so far I have removed the engine, gearbox, steering column, front suspension and will be taking out the electrics and renewing them - why, when the original exercise was to rebuild the engine - well the engine bay could do with a coat of paint to start with, the wiring looks moth eaten, the steering box looks to be leaking a little and is in the way of the painting anyway. Having trouble with the typing this morning so can not move the signature down? can't think why Bob

 

[EV2239]

Dennis Welch does valve stem seals and matching springs. Oil consumption is more likely to be excessive oil in the rocker cover because of worn shaft and bearings going down guides that will also be worn.

Valve stem seals can be replaced without removing the head, you just have to make a tool to hold the valve shut and do it at TDC so hopefully it doesn't drop into the engine.

We do this all the time to six cylinder post war Bentleys (the eights suffer too). Oil consumption is 85 MPP before and several hundred up or more after.

The only things that actually force a rebuild are big ends when they eventually rattle.

 

[me61ic]

I guess I just wanted a push towards the go ahead line... I'll be doing a wet compression test just for the fun of it, but I'll take away the head to have the valve seats + guides redone to also use unleaded fuel, I'll also replace the piston rings while I am at it and also all engine + transmission seals (At the time I have to put shelves under the car to collect all the oil mess)

 

[Johnny]

Hi again, on my BJ7 I had similar compression results. I did have two burnt exhaust valves which is common. All I did was remove the cylinder head replaced the two exhaust valves and lapped in the remaining valves. With the head off I did clean up the combustion chamber. Since I don't drive the car that much I didn't replace all the valves with hardened valves and seats. I did replace the head gasket and both intake and exhaust gaskets and of course rebuilt the carbs. My car only had about 44K miles on it and I felt a complete rebuild unnecessary. The car runs great by the way and I have driven it about 4K miles, with very little oil consumption. With the head off you can check the cylinder walls especially at the top of the piston travel for wear and unevenest.

 

[Keith_M]

Oil consumption is more likely to be excessive oil in the rocker cover because of worn shaft and bearings going down guides that will also be worn.

X2. Before you remove the head, look through the oil filler cap and see how much oil you're getting from the rocker arm. Ideally, it should barely seep out at idle. If you have oil squirting up at idle, you probably have way too much oil in the upper end and it's leaking down through the guides. Get a new rocker shaft and rebush the rockers to take care of the problem. It's not all that expensive and not all that difficult, and can make a big difference in oil consumption.

Keith

 

[TimK]

This is my oil leak story. I haven't done it, but a good suggestion (from Randy Forbes, I think) was to use copper crush washers under all the transmission cover bolts. I'd also suggest using aircraft Hylomar sealant on the gaskets and bolts.

 

[Bob_Spidell]

Cool ... a Rorschach Test for Healey owners!

 

[EV2239]

On the question of sealant I cannot recommend Loctite 5699 too highly. It' not expensive and it seals gaps of up to 1mm, it doesn't clog oil ways, it's easy to clean off and the seal breaks easily.

Most old engines don't have very rigid blocks, so as the revs rise so does the vibration and if you keep going all the sump bolts fall out! A friend who was an engineering student back in the sixties told me that happened with most Brit engines of the time at much over 4000 revs, so Loctite Threadlock on the sump bolts is good too.

I'm depressed to think I've been using both for 40 years now!

 

[me61ic]

X2. Before you remove the head, look through the oil filler cap and see how much oil you're getting from the rocker arm. Ideally, it should barely seep out at idle. If you have oil squirting up at idle, you probably have way too much oil in the upper end and it's leaking down through the guides. Get a new rocker shaft and rebush the rockers to take care of the problem. It's not all that expensive and not all that difficult, and can make a big difference in oil consumption.

Keith

Keith, I started the engine yesterday for the last time before taking it out of the car, I'll be preparing and disconnecting stuff during the week, and plan to take engine+gearbox out on Saturday. I filmed a couple of videos at idle with the oil cap out, but could not see much oil squirting. I have uploaded the videos to youtube, what do you think (by the way the engine is not that noisy, but the wind produced by the fan was almost a hurricane) I have also recorded the Oil Pressure, don't remember who asked what the pressure was, by the way what is the normal pressure for this car?

https://www.youtube.com/watch?v=TdQ99UNXwC4

https://youtu.be/75VLqCIlm1A

https://youtu.be/_d2Xq3gp0qI

https://youtu.be/jMyg9VShR3k

 

[Keith_M]

It's a little hard to tell how much oil you have coming up through the rockers from the video, but it doesn't look excessive. Mine squirted a full inch even at idle. In reading back through the posts in this thread, it really sounds like you're leaking the oil rather than burning it. Leaks come from everyone on Healey's. The rear main is a common place, but usually only after turning off the engine.

I don't know what's "normal", but in my freshly rebuilt engine oil pressure is about 40 psi at idle and 60 when driving.

It sounds like you're taking the engine out of the car, so I think the advice given sometime earlier in this thread is sound. Tear it down and rebuild as necessary. If you're doing anything with the valves it makes sense to put in hardened seats.

Keith

 

[TimK]

My healthy engine with 100,000 miles and new rocker arm shaft and pedestal bushings has 60 psi when cold and 40 when hot. Hot idle is 20 psi. I use 20w50 Castrol.