Hi, I need some advice. I am heading to our local club store in search of a good head for my Mk III tomorrow. After getting the new gearbox in I had a bit of a moment with a lot of missing and backfiring. That looks to have been a faulty condenser but in the process of diagnosing the problem I found low compression on #5. I got the head off this afternoon and although there are a few light scores on several of the bores I think they will hone out ok and there doesn't seem to be a lot of wear. The low compression is a slightly burnt exhaust valve so overall not too big a problem.
When I cleaned up the head though I found a crack between the spark plug and port. The seat is ok and the area seems to have been welded previously. My question is, this had caused no symptoms and if the crack is in an area with no water jacket, is it a problem?
If I have no joy finding a good replacement I will investigate getting it welded again.
Repairing and welding alloy cyl heads is no big deal today for any professional shop (a friend of mine Basil at 'Headworks' does this type of work for a living on modern, veteran, vintage cars and motorbikes)
I'd be more concerned about the reason some of the cyls are 'slightly' scored. It truly wouldn't hurt to remove the pistons and check the rings & lands for wear/damage. Leaving broken rings in place certainly won't improve matters over time. If the engine is well used odds on that the oil rings are jambed well into their lands. Side clearance on the ring lands should be no more than .004". You may find the top compression land which takes the brunt of the fire storm during the power stroke the worse for wear. Wishful thinking without properly assessing some of the major components won't lesson any undesired mechanical grief further down the track if left unattended. You know the adage a "stitch in time ....
Hi Vince Yes, the engine ran ok, didn't use any coolant or have any untoward noises however it used about a litre of oil every 300 miles and blew a nice plume of smoke after decending any sort of decent hill. So I had planned on taking the sump and head off at some stage and hopefully getting away with a set of rings and a hone. The engine has had some sort of overhaul but largely sat unused for the past 20 years. When I did the gearbox, I replaced the rear crank seal and took the opportunity to check a big end. The shells appear to be new with the journal I measured only 0.0003" out of round.
So this loss of compression has bought that job forward. If this results in a motor that is good do another 30k miles I will be happy with that. From there, assuming the relationship lasts, a long term overhaul of another motor would be my plan. I'm not very good at long term projects with a car in bits.
I'll post an an update on what I find when the pistons are out. As far as the head goes, I will know today whether the club has a spare and if not we have a good engine reconditioner here in Wellington who should be able to weld and remachine mine. Hopefully the crack doesn't reoccur.
I can't see any issues with the cyl head repair if the shop knows how to do these things properly Martin. My mate Basil welded up a now rare Harley Davidson alloy crankcase that had a crack going through it for me. Preheating the case initially, then TIG welding the repair and finally thermally wrapping it and allowing it to cool very slowly over about 6 hours. Similarly I've had a cracked cast iron car cyl head repaired by first having it heated over a brazier before any welding took place.
Problem solved for the head. I called around to confirm the right place to get my head repaired and was offered a good head for $200. Probably less than the welding before the machining was started.
I'm going to do a search but do we have a view on the wear limit for valve guides. I have found a huge 0.8mm valve tilt limit for a Porsche engine and my Z24 Nissan lists 0.2mm. My old head had about twice that and the new one is about at the 0.2mm. The engine was burning quite a bit of oil, probably much of it down the guide clearance. I plan on fitting modern stem seals so leakage down the guides shouldn't be a problem.
Just had a read of David's 2018 valve refurbishment thread. Looks like a bit of work ahead!
I've had a long break over Christmas, heading back to work on Tuesday after four weeks much of the time spent working on this engine. Once I got the head issue sorted it was time to have a look at the block. I cleaned all the carbon off only to find that my tale of woe continues. It looks like this engine has been well overheated at some time as there are visible cracks between the valve seats and bores on #3, 4 and 5.
The interesting thing is that as I wrote earlier, the car was using no coolant and apart from high oil consumption performed quite well. Either these cracks are not yet to the water jackets or have been sealed internally with Irontite or something similar. This actually looks likely as under magnification there seems to be some sort of hard material extruded from one of the cracks onto the combustion chamber.
At this stage, I can't face pulling the motor so have decided to re treat the engine with another dose of Irontite and see how long it lasts. It should give me some warning when the cracks develop. Fortunately I have managed to buy another complete MK III engine that is apparently in good condition so that will be waiting for when this one decides to call time.
The head I bought is in good nick and now has modern valve seals fitted. This turned out to be a cheap and relatively easy modification. With a heat gun directed into the relevant port for a few minutes, the guides pushed out quite easily and I machined the top down to remove the old o ring groove. Then turned a straight section to take the new hat seals which were only $3.54 each. These are a steel shell with a three lip oil seal moulded to them. The aluminium punch I made to refit the guides also served to fit the new seals as these are a press fit to the guides.
I pulled the pistons and gave the bores a hone, not quite able to remove the scoring completely but as this is now a short term fix probably not an issue. The engine previously had 140 psi across all cylinders give or take so reasonable compression. The three piece oil scraper rings were loose in the bores with no expander. Not sure whether this was by design or a part left out. The lack or tension also points to overheating I think if there was not supposed to be a backing spring. The new rings are a four piece design and were a bit of a B****r to fit as they were inclined to step out of the groove when fitting the ring compressor. the old compression rings still had some tension but were quite worn in their groves. The new rings are at top tolerance for clearance but should be better than before.
So I got everything back together on Monday, went through the start up routine, reset the tappets once the engine was warm and all seemed ok. I filled the coolant with water only as the plan is to reseal the system however there is no exhaust gas in the water according to my tester so the previous repair is still working.
I was a bit dismayed to say the least when I reversed the car back into the garage and found a pool of oil had developed while I was doing the initial warm up. I did a long day leading up to fitting the head and followed the workshop manual to the letter. Also unfortunately didn't notice that the head set didn't come with the sealing o ring for the back of the head. No mention of this in the instructions either.
I found an old thread from back in 2014 discussing this o ring that is only fitted to later model engines. I think I am right that it is an 020 British size which is a 0.07 section and 7/8" inside diameter with a 1" OD. I will buy one next week and when the replacement head gasket arrives will pull the head again. Fortunately during the down time waiting for the rings to arrive I pulled the LH front suspension apart and replaced the boots and bushes. In the process I found that I needed new brake pads, surprising that the car passed it's last WoF with 2mm of material remaining. So the freight cost for the second head gasket will be shared with the pads.
Does anyone know if it is ok to leave the rockers attached to the head if only the head gasket needs doing? I don't plan on removing the inlet manifold this time or anything else that can stay in place.
Not sure which comment you're referring to Phil but the valve seat I'm referring to is the exhaust seat in the block. Similarly to my SV Harley an exhaust seat in the block tends to cause cyl distortion for obvious reasons although the Rover block is a substantial chunk of cast iron.
There seems to be a common thread here, a crack in the head hear the inlet valve seat, cracks in the block adjacent exhaust valve seats. I wonder if a PO put in new valve seats enthusiastically and without cleaning the valves seat recess adequately. The Rover OEM seat replacements have a massive 7-8 thou interference. Given that the seats are nearly as hard as granite, that means the head of the block has to distort by 7-8 thou when you install a new OEM seat. In contrast, a modern universal seat has 1-2 thou interference.
My feeling is that a single crack in the block by the valve seat is just a hostage to fortune. Three cracks should be a "no-brainer".
I agree, the engine has had a previous "overhaul" and I think has had new seats fitted. It looks like some sort of tool was used to get under the seats to remove them. There are chips of cast iron missing under a couple of the seats.
Also, the valve that had burnt probably never sealed properly as when I cleaned up the rest of the exhaust valves, some were slightly burnt on one side of the sealing face.
My original plan prior to finding the cracks was to replace the full set of exhaust valves. When I found the cracks, this changed to creating a reasonable engine that will hopefully last a while.
The valves are stelite or similar faced but I found that a carbide tip would take a cut so decided to reface them on the lathe. When they were set up with the shank running true the sealing face was running out and the first cuts, only a few thou, only took metal off the good surface. When they cleaned up, the last bit to clean up was the most burnt. So the seal was reliant on the clearance in the guides to allow the taper to pull into the seat.
I haven't used a valve grinding machine but I assume they hold the valve in a collett that should ensure the valve runs true. There must have either been some rubbish between the stems and the collet or more likely between the collet and the taper in the machine.
All of which points to a very poor quality job. So although the oil rings having lost their tension indicates the engine getting hot, it is quite possible that a ham fisted mechanic could have don emperor the damage either removing or refitting the seats. Perhaps both.
Hopefully my replacement engine has had a happier life!
The reason for the larger/tighter interference fit on the exhaust side of the Rover 3 litre is due to the heat the cast iron block retains...funnelling exhaust gases through the block (similar to Henry Ford's SV V8s) doesn't help the situation either. Alloy heads can use less interference fit by virtue of the material dissipating heat more effectively.
So the head gaskets arrived, everything went back together ok the second time and the engine is running pretty well. I was pretty disappointed with the amount of oil smoke on the first run but that seems to be improving as the rings start to bed in. Time will tell if the cracks in the block are going to grow and open but the spare engine I now have can go in when the time comes.
I have one one more question to end this tale.
I took the car car for a WoF yesterday, no repairs required and set off for a legal drive. The first 50 had been at risk of Mr Plod taxing me for driving without a current one as it expired while the repair was going on.
I arrived home to find that somehow the fan had worn a hole in the top radiator hose and yet another repair needed. As an interim measure I went to a local parts supplier and spent half an hour looking through their stock of thousands of hoses and ended up taking three likely prospects to try.
The one I fitted is perfect except it is not the original gaitered type, just a formed hose the correct shape to go between the thermostat housing and the radiator. I don't have a huge problem with getting another gaitered hose from JRW but is this necessary as the one that wore on the fan was only a few months old and the one fitted has better clearance. Do the 3 litre engines torque so much that this is required so that the radiator doesn't get stressed? The car had a plain hose on it when I got it.
Geez Martin...you've just completed a fairly intensive rebuild of the engine and you're concerned about an OEM convoluted radiator hose! 🤔
For whatever my opinion is worth, as long as there's adequate clearance...use the hose that you sourced...it's only channelling coolant.
As an aside, a now departed friend of mine had a pristine manual Mk3 coupe (5 speed self adapted to the 3 litre) and I never recalled an issue with the engine torquing over to one side or the other and allowing the fan to either contact the radiator hose or stress the radiator core! Lovely car to drive and perfectly maintained but it was definitely no big inch hemi V8 (that would definitely torque over in the engine bay)
Although when I fitted the P76 V8 to my MK3 many years ago the engine did torque the frame causing the radiator to start weeping between the core and the header tank. I had it resoldered several times and it would last for a month or so...then start weeping again.
The radiators on the Mk3s were solidly mounted to the body as I believe most 3 litre P5s are. The V8 P5Bs are flexibly mounted. I solved my radiator issue by mounting it at 4 points with rubber bobbins.
I would go with a moulded hose rather than any concertina hose. The latter are formed in two halves and glued together. They can split.
I had a bigger problem with the shape of the fan guard, which varied a little between cars. It impinged on the top hose and to avoid the hose leaking, I had to reshape the guard to make more clearance.