Rebuilt Mi Is Knocking During Running In Process

[WildCards 0]

I've been running in my rebuilt Mi engine now the car is finally finished but last night it started knocking. I've got 20w50 rubbish oil in the engine and yesterday covered 230 miles at no more than 3000revs before changing the oil and filter for the same but new, rubbish 20w50 oil. I set off again to do another 200 miles-ish revving to no more than 4.5-5k, but 30 miles in I get a knocking noise coming through.

 

It knocks under load quite loudly, but when I lift off it's gone, it knocks extremely feintly on idle once warm, but doesn't knock at all at idle when cold. I've checked that nothing is loose, i've checked all of the mounts and i've had a screw driver to the block with my ear on the other end to see if I can hear an amplified metal on metal sound, I can't. It still makes good oil pressure and has plenty of oil in it and recieved a new oil pump and uprated spring when rebuilt

 

I've spoken to a mate who seems to think it could be a stuck tappet as the noise is more pronounced from the top of the engine than the bottom and I've also spoken to Darren at Spoox who thinks it may be a main bearing failure or a spun shell, although he hasn't seen it in the flesh, just commented from an over the phone description.

 

Despite being MOT'd on friday, two driveshaft boots have also split and a gearbox seal has gone. Marvellous!

 

 

Thoughts appreciated?

[James_R 3]

Is it making good pressure oil wise when hot??

 

the fact it's only on throttle doesn't sound right to be a shell, it's more of a rumble which gets worse as the revs go up, but tends to be revs linked not throttle.

[snooks 5]

As it doesn't take long to whip the sump off there's no harm in checking the big ends. Will give you piece of mind with the bottom end at least.

[Miles 331 1 Cars]

Could be a cam lobe worn, I;ve come across that before but they tend to knock all the time, Other than that as said whip the sump off and have a look, also draining the oil is a good sign if anything has happened internally

[WildCards 0]

Cheers for the replies chaps. It makes good oil pressure in every situation from what i've noticed, certianly at idle, under load, engine hot and cold. Whipping the sump off makes good sense, i'll drain the oil and see if that holds any clues then have a butchers into the engine with the sump removed and see what I can see. Whatever it is, I really hope it can be fixed easily enough, this bloody car has cost be an arm and a leg recently.

 

I should add that the knock/noise is at it's worse when the engine nears the 3k rpm figure, but is still quite significant at higher revs.

Edited February 22, 2009 by WildCards

[cir287 0]

I had something similar before, just after a rebuild on a 16v. I just got a bit of running in on the engine and then the knocking started, it lost some power too. this knock was quite pronounced at anything much above tickover.

anyway I whipped the sump off and took a look, turned out to be a main bearing, it was a really stupid mistake on my part, I got distracted while building the engine and left it halfway through fitting the main caps, anyway I ended up fitting two middle ones in the wrong places. everything else was perfect but this was enough to cause the damage.

 

as it was a race engine I didnt want to get a regrind on the crank, I did manage to hunt down a reasonable fresh crashed mi16 in a scrapyard, had to buy the engine but still a hell of a lot cheaper than buying a new crank. ended up using a lo more of the remaining bits than I thought over the following year.

 

hope you have better luck than me,

[petert 554]

as it was a race engine I didnt want to get a regrind on the crank,

 

That doesn't make sense. Wouldn't you rather a "round" 49.70mm crank, than an "oval" 50.0mm crank?

 

It does sound suspiciously like a rod bearing. Did you get the crank ground during the rebuild?

 

As good Mi16 cranks are getting rare, I get them nitrided as a well now, during the regrind process. It won't help spinning a bearing, but the crank might just come through unscathed.

[Stu 18]

Sounds more like a little end rather than crank, especially as you see the knock under load.

 

Another thing to try and rule out is that the noise is a knock rather than 'pinking' noise, is it on Mi management or are you using the 8v dizzy setup? if its the latter id try knocking a little advance off and then trying it.

 

If the oil pressure is good when it knocks then you can *probably* rule out the crank or a shell.

[SweetBadger 91]

I had a similar problem when running in my MI after a rebuild... Good oil pressure but knocking, worse at 3000rpm on light throttle.

 

Turned out to be an ovaled rod that I'd missed during the rebuild - It was obvious that there was a problem because the bearing shells on the rod in question literally fell out of the rod/cap and had a polished finish where they had been rubbing on the crank (real give away was that thw big end cap wouldn't go back onto the journel without a bit of persuasion!). Bloody pain in the arse as the head and sump need to come off to replace a rod. Was lucky enough to have not caused any significant damage to the crank, so it was fine after replacing the rod.

 

First thing I'd do is take the sump off, then providing there's no obvious major damage, pull the big end bearing caps off and inspect the shells for any signs of premature wear/damage. If the big ends look ok then you could check the mains too for peace of mind...

[WildCards 0]

Did you get the crank ground during the rebuild?

 

Yes, crank was ground.

 

Cheers guys. I'll take a look.

[Alteran 1]

Isn't 20w50 oil a little thick for that engine? I know putting a thick oil in certain engines will cause the hydraulic tappets to chatter. My knowledge on this engine is quite limited so forgive me if this has solid tappets. I'm just thinking if your mate is right in his top end diagnosis.

[nick 3]

Has it knocked out a big end before? if so, was the rod replaced? 99% sure that the rod will be scrap and should have been replaced.

 

Nick

[Tom Fenton 1,526]

The rods can usually be reclaimed, however if it has spun a shell in the past the rod will need some work.

[boombang 2]

Had this but it was more of a rattle than knocking. Could not place it in the engine though, sounded like bottom end but turned out to be worn valve guide on exhaust side.

[pug_ham 242 3 Cars]

Has it knocked out a big end before? if so, was the rod replaced? 99% sure that the rod will be scrap and should have been replaced.

This is what I'm going to ask.

 

Why did you rebuild it & was it all fine before the rebuild.

 

Like Nick has said if you rebuilt it due to a spun big end bearing but didn't replace the associated rod or get the crank checked to be 100% straight then you'll probably have spun a big end bearing again meaning you need a new rod & most likely crank because when they go the crank can get bent.

 

Graham.

[WildCards 0]

I originally had the engine rebuilt because it was an unknown, it came to me as block and head, not taken out of a car. When I had it rebuilt the chap measured the tolerances and stuff and told me it would be fine.

 

Anyway, I took the sump off at the weekend and it's spun a shell, the crank is marked but not grooved or pitted so i'll whack a new bearing onand see how I go, if it spins again i'll look at getting the crank checked and polished/ground. Thanks for the replies though.

[Dave_McC 0]

I'm no expert on engine building - having built 2 in my whole life - but if it's spun a shell once you need to find out why and fix the problem - just replacing the shells will result in exactly the same thing happening again - possibly with far more catastrophic results for your engine than has happened this time.

 

Dave

[WildCards 0]

That's a fair point Dave, but where do you stop? in reality the engine needs to come out again and have the crank and rods checked for damage/ovalling. I may aswell chance it and if it does go again I know it'll need doing properly. Shells will cost £60 and I can fit them myself, it makes sense to me to rule out the cheap and simple things first.

[Tom Fenton 1,526]

If you put another set of shells in you are just wasting £60 as the same thing WILL happen again. Not to mention other associated damage that will be caused by the debris going round the oil system, the oil pump will be knackered for example. A shell spins because it is not being clamped properly by the con rod, because the con rod has been worn oversize. Bite the bullet and do it properly once and for all, as otherwise you may as well throw your cash down the bog.

As I said before, the rods can be reclaimed by a machine shop by machining a small amount off the mating faces to close up the "hole" and then bore it back to round once more. I have had this done successfully more than once before.

[SweetBadger 91]

If you are absolutely sure that the crank is not to blame, you can replace the rods with the engine in situ without disturbing the piston rings if you are careful.

 

Providing the crank measures ok, take the head off then remove the liner, piston and rod without removing the piston from the liner. Then carefully slide the piston down the liner until you just have access to the pin. Remove the retaining clip, slide the pin out, replace the rod and push the piston back up and put it all back together...

 

Pain in the arse as you'll need new head bolts and gasket but preferable to wasting £60 on new shells only for the same thing to happen again. I'm sure there must be plenty of good second hand rods available if you ask around.

 

As already said the shell spun for a reason and if you don't find out why its very likely to happen again.

[welshpug 1,627]

Don't forget the liner seals if you take the head off

[RonnieG 0]

I agree with most above - You need to deal with what caused the shell to spin or it's just going to be another £60 down the drain!

 

It's expensive in time but it's not going to cost you too many pounds to whip the head off again to remove the piston and swap/sort that rod.

 

A second hand rod is also pretty cheap and a much better risk if you buy it from someone on this forum who already knows it's a good one and you can also get it checked/measured before refitting.

 

Pain in the ass but one of the risks using 'unknown' engines......

[WildCards 0]

I appreciate your advice chaps, i'll let you know how I get on, but TBH, after having the engine rebuilt once and it to fail within 300 miles I'm thinking of maybe going down the GTI-6 route anyway. Or just binning the entire car and getting something else.