Catcams Jamming In My Head!

[RobMGti 0]

Your funeral man, id agree with some of the above comments. Its seems like there should be a far easier solution than the route you are going down.

 

With far less Danger! As i always say in times like this, if you die..ill have your stuff!

Edited January 19, 2006 by RobMGti

[Hilgie 16 2 Cars]

I haven't read anything about it in this topic, but Kristian said that the cams did fit another Mi head he had lying around. So it's definately the head that is faulty here. Nothing to do with the cams.

[petert 550]

And presumably there's no chance the caps got mixed up with those from another head at some time?

 

This the most likely explaination.

[B1ack_Mi16 67]

This the most likely explaination.

 

If so, that must have been before I got the head, as I only had 2 heads when I started this projects, and the other head has the right caps, and cams rotate fine in that one.

 

I'll just wait and see, the guy was gonna make it work, and as long as the cams will turn freely I'm more or less pleased with that. Just get the engine together and see how it performs.

[B1ack_Mi16 67]

Been @ my engine builders place now.

 

All the caps are approx 0.1mm out, so it's now beeing shipped to Sweeden for line-boring (too expensive in Norway). So it'll be good in the end. The line-boring is just another expensive experience, but I've learned to always check that the caps will match the head before doing expensive work to it. The line-boring is costing 210£ quite a bit, but still cheaper than the 400£ it cost in Norway

[niklas 1]

Who's doing the job??

[B1ack_Mi16 67]

Who's doing the job??

 

Not too sure, but it's a guy that my engine builder always uses for this kind of thing.. My crank were offset-grinded at the same place.

 

Think it's in Östersund somewhere (only approx 3-4 hours drive from Trondheim), the guy's first name is "Lennard" or "Lennart" or something like that, he runs a business over there.

[M3Evo 0]

Won't you need cams with bigger journals if the head's been line bored?

[B1ack_Mi16 67]

Won't you need cams with bigger journals if the head's been line bored?

 

Caps will be ground down a tiny amount, and then the you bore..

[PumaRacing 1]

Caps will be ground down a tiny amount, and then the you bore..

 

Won't work. Think about it.

 

If the caps are horizontally misaligned then grinding a tiny amount off them vertically won't solve that. You'd have to grind enough off them such that the length of the chord subtending the base of the cap fell by twice the amount of the misalignment. i.e. for a 22m bore which is 0.1mm misaligned you need the chord across the base of the cap to drop to 21.8mm so that no part of the cap now overlaps the semicircle of the bore in the head.

 

That's a fairly simple mathematical problem to do with chord lengths and depths and the answer is you need to grind 1.48mm off a 22mm diameter cap and 1.41mm off a 20mm diameter cap to solve a 0.1mm horizontal misalignment so that the caps can then be rebored back to nominal size. I very much doubt if you can take that much off a cap and it still remain functional.

 

Alternatively you don't bother grinding much, or indeed anything off the caps and live with the fact that after boring they'll be aligned with the head on one side but still 0.1mm too big on the other side. Can't see that being very good for the oil pressure in the bearings.

 

This entire sorry saga mystifies me. How come you are only now finding out that the caps are not the right ones for the head? Why does a standard cam rotate in them ok but not the Catcams one? I thought you checked the alignment with a fingernail as I suggested and thought the caps fitted ok.

 

Where did the correct caps go to? Maybe they're on one of your other heads. Why not first try every cap you possess in the hope that you find a set that fit well enough for the cams to rotate?

 

Are you absolutely sure your machinist knows what he's doing and that the problem really does lie in the caps?

 

Finally. There's a possible free solution. As I understand it two of the caps are ok and three are not. Remove the dowels that locate those three so that only the bolts hold them in place. Maybe that will give them enough free play to move sideways a bit and align with the cams.

[petert 550]

If the caps are horizontally misaligned then grinding a tiny amount off them vertically won't solve that.

 

Is it going to matter if they don't totally clean up in the line bore process? Surely as long as the high spots are removed, a low spot on the other side won't cause any drama?

[PumaRacing 1]

Is it going to matter if they don't totally clean up in the line bore process? Surely as long as the high spots are removed, a low spot on the other side won't cause any drama?

 

A bearing that's the right height but 4 thou too big on one side isn't exactly a great shape for developing the hydrodynamic lubrication film that prevents metal to metal contact. Frankly I don't know exactly what would happen because unsurprisingly I've never come across a bearing shaped like before.

[B1ack_Mi16 67]

A bearing that's the right height but 4 thou too big on one side isn't exactly a great shape for developing the hydrodynamic lubrication film that prevents metal to metal contact. Frankly I don't know exactly what would happen because unsurprisingly I've never come across a bearing shaped like before.

 

The guy doing the work in sweeden is indeed very good.

the misalignment wasn't sideways, it was mostly in the height direction (as I couldn't really see there was a mis-alignment at all).

 

I got the head with a car I bought for 5 years ago, so no point in trying to find out where the correct bearings are. Probably been scrapped now when the other guy with the wrong bearings found out.

 

And the standard cam rotates most likely because it comes from a 250000km engine and the journals were worn a little.

[PumaRacing 1]

The guy doing the work in sweeden is indeed very good.

the misalignment wasn't sideways, it was mostly in the height direction (as I couldn't really see there was a mis-alignment at all).

 

I got the head with a car I bought for 5 years ago, so no point in trying to find out where the correct bearings are. Probably been scrapped now when the other guy with the wrong bearings found out.

 

And the standard cam rotates most likely because it comes from a 250000km engine and the journals were worn a little.

 

If the caps are aligned correctly in the horizontal direction then they're almost certainly the right caps. Maybe some of the bores are a fraction on the small side of tolerance and the new cam journals are a fraction on the large side but I still think you don't really have a problem that wouldn't sort itself out as soon as the engine started up.

 

If an old std cam rotates fine why not just polish down the journals on the new cams by a thou which is a quick job on a lathe with wet and dry paper or your local crank grinder could do it in a few minutes. Bloody sight easier and cheaper than line boring a head which has two different sized bearings to deal with. I hope the bloke doing it realises that and doesn't just bore them all to one size.

 

If I'd had the head and cams here I'd have sorted the bloody thing out in less time than I've spent typing advice.

[B1ack_Mi16 67]

If the caps are aligned correctly in the horizontal direction then they're almost certainly the right caps. Maybe some of the bores are a fraction on the small side of tolerance and the new cam journals are a fraction on the large side but I still think you don't really have a problem that wouldn't sort itself out as soon as the engine started up.

 

If an old std cam rotates fine why not just polish down the journals on the new cams by a thou which is a quick job on a lathe with wet and dry paper or your local crank grinder could do it in a few minutes. Bloody sight easier and cheaper than line boring a head which has two different sized bearings to deal with. I hope the bloke doing it realises that and doesn't just bore them all to one size.

 

If I'd had the head and cams here I'd have sorted the bloody thing out in less time than I've spent typing advice.

 

The problem would certainly not work itself out with just starting up the engine, I tried to rotate the cam with all my force, both hands, and couldn't get it to rotate one single degree, it was totally stuck.

 

I see that the cams could be put in the lathe and journals sanded down a bit but now it gets fixed and linebored. He had linebored Mi16 head before as some of the bearings were so bad they had to be welded on an engine he did for someone 8years ago, so he's totally aware of the differences in the bearing-diameter.

[Dom9 2]

The problem would certainly not work itself out with just starting up the engine, I tried to rotate the cam with all my force, both hands, and couldn't get it to rotate one single degree, it was totally stuck.

 

I see that the cams could be put in the lathe and journals sanded down a bit but now it gets fixed and linebored. He had linebored Mi16 head before as some of the bearings were so bad they had to be welded on an engine he did for someone 8years ago, so he's totally aware of the differences in the bearing-diameter.

 

Well, it may well have sorted itself out! You trying to run it with your hand is probably the equivalent of 0.001bhp, whereas the engine, even at idle is probably around 50bhp and 1000rpm and would have soon worn the bearing caps, as long as they were lunbricated and didn't seize!

 

Again, if the head is being linebored, as Dave said, won't the cam journals then be too small for the bearings??

[B1ack_Mi16 67]

Well, it may well have sorted itself out! You trying to run it with your hand is probably the equivalent of 0.001bhp, whereas the engine, even at idle is probably around 50bhp and 1000rpm and would have soon worn the bearing caps, as long as they were lunbricated and didn't seize!

 

Again, if the head is being linebored, as Dave said, won't the cam journals then be too small for the bearings??

 

Well, I don't exactly know what they do, but they're gonna fix it so it's spot on.

They might as well weld the journals first before doing the lineboring, I don't know really.

 

And now I don't care too much either, as it's getting fixed. He talked about grinding a little bit off the caps and then do the lineboring, and since it was not very much out sideways anyway I believe he can get away with very little grinding. Then the journals on the cams are supposed to be standard dimention.

 

It's the same when repairing a rod that's spun a shell. Grind a little off the cap (maybe also rod itself?) and then rebore + hone the big end.

[petert 550]

The problem would certainly not work itself out with just starting up the engine,

 

Particularly if the journal picked up on the aluminium, cam stops, cam belt brakes, valves bent, guides cracked etc. !!!

 

A extra few dollars sorting the head out is cheap insurance considering the amount you've spent on the rest of the engine.

[PumaRacing 1]

Well, it may well have sorted itself out! You trying to run it with your hand is probably the equivalent of 0.001bhp, whereas the engine, even at idle is probably around 50bhp and 1000rpm and would have soon worn the bearing caps, as long as they were lunbricated and didn't seize!

 

Again, if the head is being linebored, as Dave said, won't the cam journals then be too small for the bearings??

 

No, they machine a bit off the base of the caps to gain some metal to play with in the vertical direction and then linebore back to std diameter. Same process as honing oval conrod big ends back to size. The trick is to align the boring bar exactly in the horizontal direction because you can't afford to make that any wider and then take a couple of thou vertically off both the bottom of the bores in the head and the top of the bores in the caps. It's a nasty fiddly exercise though and if there is any twist in the head it becomes close to impossible unless you set up the boring bar for each cap separately. When the main caps of engine blocks are linebored it's normal to enlarge them by 0.4mm which allows for any twist or bend in the block and then oversize shell bearings are available to suit. Not possible in this case with a set cam journal size.

 

I wouldn't have gone this route in a million years. 1st choice would be polish a bit off the cams until they turned easily. Try each bearing cap in turn and just polish the cam journals down on the ones that stick. 10 minute job in the lathe.

 

2nd choice if there was some overwhelming reason not to touch the cams would be to put a fixed reamer or adjustable hand reamer through each bearing in the head in turn to nip that missing thou or two out of them. I even have 20mm and 22mm reamers in the workshop. Even buying new reamers if you didn't have them would only have been £20 each or so as they are std sizes. Bit fiddly getting a reamer into the centre holes but some sort of extension bar could be rigged up easily enough to drive it from the end of the head. The advantage of reamers over line boring is they self centralize in each hole and only take off the unwanted high spots. Setting up a line borer accurately across five separate bearings up to 18 inches apart is a real PITA if you can't afford to make the holes any bigger than std size. I'd give the process fairly high odds of getting screwed up and wrecking the head.

 

Either of the above could have been done by Norwegian engineer chappy at very little cost without sending the head off to another country. Anyway, not my problem I suppose. I'm just a bit gobsmacked at the enormous amount of arsing around that this trivial little problem has turned into.

[petert 550]

2nd choice if there was some overwhelming reason not to touch the cams would be to put a fixed reamer or adjustable hand reamer through each bearing in the head in turn to nip that missing thou or two out of them. I even have 20mm and 22mm reamers in the workshop. Even buying new reamers if you didn't have them would only have been £20 each or so as they are std sizes. Bit fiddly getting a reamer into the centre holes but some sort of extension bar could be rigged up easily enough to drive it from the end of the head. The advantage of reamers over line boring is they self centralize in each hole and only take off the unwanted high spots.

 

How could a reamer be any good? Just another bodge. A reamer can only make a round hole bigger. If there's two semi-circles, how does the reamer know which is the correct centre?

[PumaRacing 1]

How could a reamer be any good? Just another bodge. A reamer can only make a round hole bigger. If there's two semi-circles, how does the reamer know which is the correct centre?

 

Do pay attention dear. Kristian said some time ago that it wasn't a horizontal alignment problem i.e. the caps were most likely the right ones for the head, but according to his machinist the bores were just a fraction tight in the vertical plane. If another cam rotated fine then all we're talking here is a thou maybe. Without measuring everything myself I'm struggling to accept much of the entire saga at face value. I find it vanishing unlikely that an old head would still have tight bearing bores due to a factory machining error after running ok previously which clearly it did or the bores would have seized on its original cam.

 

Frankly this could really have been down to anything. Burrs, slight bend in the head which afaik no one has checked yet, stack up of tiny tolerances on cam journal size v bearing bore size or maybe even nothing to do with circular clearance at all. The front or back of a bearing journal might have been catching on the front or back of a cap.

 

It needed a really competent engineer to investigate each bearing in turn with engineer's blue to find out what was catching on what, check the head for bend and measure everything with high precision before deciding how best to correct it BUT you can't get away from the fact that std cams rotated fine in the head.

 

That means the head itself just can't have been outside factory specs and a hugely expensive line boring operation just ain't the way to go. Line boring is what you need to correct big errors in twist, bend or size and ideally by machining oversize for bigger bearings. Trying to use it to correct a tiny error is bloody stupid because you can't clock the line boring machine up that accurately. Something somewhere needed a tiny amount polishing, grinding, reaming, filing or however else firkling off it and the thing would be a good un.

 

Where the job went wrong was when Kristian said "I can't be arsed anymore" - not an exact quote but paraphrasing with journalistic license. You don't build perfect, or even good, engines by getting fed up and waving your hands in the air in defeat or frustration. You meticulously investigate each problem area in turn and find the optimum solution and then you apply it and move on.

 

It's a bit like raising children or having pets. Infinite patience, lots of TLC, never give in to defeat and in the end the rewards will come.