Engine rebuild

[gnotte]

Hello all,

when you regrind the crankshaft for a normal road usage engine is it necessary to have it hardened ?

thanks, Guy

[Rhodri]

My crank is, at the moment, being reground. The engineer reckoned that for normal road use it would not need hardening. However, if something should happen to the bearings, grit, low oil supply etc, then the bearings are more likely to take the damage as opposed to the crank if it is hardened . This would prevent the crank having to be reground again and inevitably weakening it. Therefore I am having mine tuftrided.

 

I think that the more important thing is very careful balancing of crank, pulley, flywheel, clutch cover, and also rods and pistons, to help delay a broken crank. This is information that I have gleaned over the years, thankfully never having had a broken crank, touch wood !!

[marvmul]

Agree with Rodrick;

Had the crank for my TR3 racecar crank reground : only the mains, - 0.010". The man said hardening was necessary, he wouldn't think of omitting that.

[Don Elliott]

I use my TR3A for driving and highway touring at 70-75 mph (110-115 KM/HR). I had the crank reground without hardening at 80,250 miles from new, then again 43,000 miles after that when I decided to go for a modern rear oil seal. I've driven it for another 51,000 miles since then with no problems. I pulled the engine last week and this afternoon I will have the bearing shells out to see how it all looks now. I don't expect anything problematic. Never had the crankshaft re-hardened.

[RogerH]

Hi Chaps,

this is an interesting subject - "to harden or not to harden". Most cranks are not hardened and last for a very long time as Don will testify. Hardening of the journals may make the crank less flexible and actually accelerate cracking, however the hardened surface is very thin and should still allow flexibility.

Normally the broken cranks, in the past, were not due to lack of hardness. Rhodri's point about balancing is well founded and beneficial.

However nobody appears to thoroughly investigate crack checking of the journals before and after machining. Where the journal (b/e & m/B) runs into the crank web some of the machining left something to be desired. Even the smallest machine tool marks are stress raisers and can cause cracking, given enough time.

If I had a crank going through the workshop I would carry out a magnetic particle inspection of the above areas before machining and immediately after machinging to ensure that there were no cracks developing in the journal web/radius.

Having done that I would ensure that this radius was blended and polished so all machine marks were removed.

I don't know if engineering workshops for car stuff do crack checking on a routine basis but they should.

Balancing - yes

Crack checking - definately

Hardening - if you like

 

Best of luck

Roger

[Don Elliott]

Further to my previous note above, I turned the engine over on my motor stand, removed the oil pan, the pump and then the bottom ends of the con-rods. The bearing shells are like new after 51,000 miles. In fact they look better than after 43,000 miles when I re-ground the crank after 43,000 miles. At that time the con-rod bearing shells were scored though the grey babbit metal and into the base copper. This time after 51,000 miles since the last re-grind, these most recent bearing shells are superb. The crank is looking great as well. In fact, I'm not going to look at the main bearing shells for the crankshaft as I'm assuming that they will look perfect as well and I plan to re-install the same con-ron bearing shells, they look so good.

 

And my crank has been ground twice and has never been hardened. I plan to put in new piston rings and finish re-assembly of the engine to have it back on the road by June.

[jonlar]

Could it be a case that if the crank journals aren't hardened they and the shells will in effect polish each other rather than causing score marks if one material is harder than the other..........

[gnotte]

Thank you to all of you, as always your answers are very adequate.

Cheers, Guy

[marvmul]

Further to my previous note above, I turned the engine over on my motor stand, removed the oil pan, the pump and then the bottom ends of the con-rods. The bearing shells are like new after 51,000 miles. In fact they look better than after 43,000 miles when I re-ground the crank after 43,000 miles. At that time the con-rod bearing shells were scored though the grey babbit metal and into the base copper. This time after 51,000 miles since the last re-grind, these most recent bearing shells are superb. The crank is looking great as well. In fact, I'm not going to look at the main bearing shells for the crankshaft as I'm assuming that they will look perfect as well and I plan to re-install the same con-ron bearing shells, they look so good.

I suppose you are very right to do so. A simple check though is putting 2 or 4 Plastigauge filaments upon the bearing surfaces, transversely, and torque the bearings caps down : comparing the width of the squeezed filaments with the scale that comes with these filaments will tell you the clearance of the bearings.

[Don Elliott]

I would if I was concerned, but the oil pressure before I pulled it apart was 70 psi cold, 20 to 30 psi hot at idle and 55 psi while driving at 70 mph. The reason I'm doing this is to find why I always had to add a liter of 20W50 every 600 miles. It's been like this ever since I re-built it 94,000 miles ago - even just after that re-build in 1990.

[jonlar]

The reason I'm doing this is to find why I always had to add a liter of 20W50 every 600 miles.

 

Hi Don, does the level keep dropping if you don't top it up, a lot of British cars can better run with oil level between the H and L marks, I was talking to an old boy with an Austin Cambridge last summer, all original with almost 100,000 on it - only ever had the head off for decoke, he was rather concerned that he had to keep topping up the oil every week to keep it up to the High mark, I suggested he run it for a few weeks (but to check the level weekly) without topping it up. When I saw him last week, he said the level dropped for a couple of weeks then stabilised and he'd done just under 2000 without a top up, whereas before it had taken ½ pint almost weekly.

Edited March 3, 2007 by jonlar

[Don Elliott]

Thank you for the suggestion. I used to keep it at the top line. I'd check it every week or so and add a bit to keep it there. I figured that more oil would keep everything cooler, therefore I figured less wear or damage internally. But a fellow TR owner mentioned that he keeps his at the bottom line. That was about 8 years ago, so, since then, I've kept mine a bit above the bottom line. And I still had to add a liter of 20W50 every 600 miles - even with it down near the bottom line.

 

I think that the piston rings are causing the crankcase to build up pressure even though it has the lower vent tube. It drips oil continuously - I see it all over my garage floor. I had a leak-down test performed about 6 years ago and three cylinders had about 3 or 4% while No. 4 cylinder was down to about 12%. On a newly rebuilt engine 2% is excellent, while racers would aim for less than 2%.

 

BTW, when I pulled the oil pan etc. last week, there was no sludge in the engine, anywhere. I quick wipe with a clean cloth and it looked as if I had used a solvent to clean it.

 

The mystery deepens.

[marvmul]

When putting in new piston rings, simple oil is best to get the rings well bedded in, and of course the liners should be honed. Especially fully (and semi?) synthetic oil can cause problems of too much oil consumption: it can prevent the rings of bedding in properly. To avoid compression leak past the rings : some ring sets come with the top ring too long in order to be able to adjust the ring gap in each cylinder individually by filing. To measure this gap, the ring should sit absolutely squarely (by pushing the ring down in the cylinder with a ringless piston). Most specialists will advise to turn the gap of the top ring away from the thrust side of the piston (so turn it to the carburettor side) and the gap of the second ring to the manifold side (turned180° away from the gap of the top ring). Never put a ring gap in the region of the piston pin ends.

Most of the oil that is picked up from the sump by the oilpump is returning to the sump after leaving the circulation via the main and rod bearings. The main bearing clearance isn't important for oil consumption, but the rod bearing clearance is : part of the oil escaping from the rod bearings is thrown onto the cylinder walls : if the clearance is too wide, it is possible that the oil scrape rings can not cope with the amount of oil.

[Don Elliott]

Thank you for all that valuable input. I bought new pistons, rings and liners as a set from Peter Hepworth himself in Yorkshire in 1988. I wanted to keep the displacement at 1991 cc and he told me to call back the next day as he'd have to search for some that he thought werre in his basement. He found what he said was the last set he still had in his basement storage area. The pistons are Hepolite with 4 grooves for 4 rings each. All this now has 94,000 miles since then and they look very nice.

 

There are brownish to black stains (like a film of "coke") on the OD of all the pistons where the wrist pin ends are found. That is, to the front and to the back of each piston. The thrust surfaces of the pistons are free of these stains, possibly because the thrust may cause some friction, or at least a wiping motion.

 

Or maybe the gaps for the top rings were not placed as you recommend.

[Don Elliott]

I've ordered a full set of new rings for my Hepolite 4-ring pistons. The engine re-build shop told me that the compression rings needed replacement. He added that it appears that my SU carbs were set too rich and the rings became worn and explains why there is a brownish film (like smeared coke) in some places on the outer walls of the pistons. The liners are worn only 0.002" at the top, only 0.001" half way down and no wear at the bottom. He's going to hone the liners and when I get the new rings (Hastings 2C6753 for Hepolite 4-groove pistons) he will check the ring gap at the bottom of the liner.

 

Marvmul. You once wrote the following. Would you (or any others) like to add why ?

 

"Most specialists will advise to turn the gap of the top ring away from the thrust side of the piston (so turn it to the carburetor side) and the gap of the second ring to the manifold side (turned180° away from the gap of the top ring). Never put a ring gap in the region of the piston pin ends."

 

I assume when you wrote "the manifold side" you meant "the distributor side".

 

Why should one never put a ring gap in the region of a wrist pin end ?

 

With 4 rings in my pistons, I was thinking of alternating the ring gaps 90 degrees apart. I was planning to set the gaps at 45 degrees to the carbs, 45 degrees to the wrist pin ends and also the distributor side. What are your comments ?

[j-eichert]

Hello Don,

 

think of maximum flow resistance: The gap is a leckage, even if it is small.

 

And the gas needs time to pass the piston rings.

Once the cylinder fires up, a shock wave is runing through the cylinder and down between piston and liner. It is stopped by the piston ring, but passes through the gap. The it has to go all the way around to the opposite side, pass the next gap....

Just turning the gap 45° reduces the way to a fourth.

So in consequence more gas will pass all rings and find its way into the crankcase. So as time is limited, the gas may not find its way out of this trap, if the way is long enough.

To make the way longer, place the first gap on the opposite side of the spark plug, where the explosion and shock front starts.

 

It may not be totally correct, but it explains what happens somehow

[marvmul]

Jon,

[marvmul]

Don, the explanation of J Eichert is what I've heard also, and it is plausible. But I've made a mistake about the orientation of the ring gaps.

The thrust side of the piston is the manifold/carburettor side : when the piston is going down, the crankpin is nearer to the distributor side and the piston is pushed towards the manifold side by the combustion. The ring gap of the top ring should be on the manifold side and not on the distributor side, because the ring is flush with the piston wall at the manifold side and the gap is not exposed there. The gap of the 2nd ring should be 180° opposite to the top ring gap, because of Eichert's explanation. The 2nd gap is necessarily more exposed because the clearance between piston and cylinderwall is located at the distributor side. Hope this makes things clearer.

[Don Elliott]

Yes it's clear. Thanks to both. I think I'll follow your advice.

 

By the way, Johannes, this is only to clarify that during combustion, in English we have a deflagration flame front. We only get a detonation shock wave where the shock wave is moving faster than the speed of sound. The flame front (deflagration moves slower than the speed of sound), therefore there is no detonation unless we get severe knocking and this knocking can damage the engine because of the severe forces of a detonation.

[j-eichert]

Don,

thanks for this clarification - in german the differentiation between pressure waves travellinmg with subsonic and supersonic moving speed is not so strict (and I larned a new word now )

 

Your experience with rebuilding (and wear) of your engine is very interesting. I will probably follow your strategy when taking care of my own engine in the near future.