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Bump clearance


Kieron G

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I see that RIchard has already dealt with your first point, . . . Thank you Richard.

 

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Vaseline works too, I don't have any vaseline in the workshop. Lots of grease though, and most boats have some

 

Richard

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Apologies for late reply ,Just noticed later posts on this thread. The procedure of using lead rod through injector hole to take bump clearance is how manual describes to do it. The engine is direct injection. I've just got gaskets delivered from 'Gaskets to go' so i'll see which method works best. Thanks for suggestions / comments on this . Can't wait to get it up and running again and try out the repitched , reworked prop.

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  • 2 weeks later...

Just revisiting this thread to correct a mistake I made when stating the engine is direct injection. As stated by Tony it is indirect . The lead through the injector hole works because it is directed onto the top of the piston by the shape of the separate cut away in the chamber. Made a statement through what I thought I remembered rather than having a proper look.

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Just revisiting this thread to correct a mistake I made when stating the engine is direct injection. As stated by Tony it is indirect . The lead through the injector hole works because it is directed onto the top of the piston by the shape of the separate cut away in the chamber. Made a statement through what I thought I remembered rather than having a proper look.

 

Taking a bumping clearance reading at just one point on the piston crown is never going to give you an accurate result because of the piston skirt clearance allowing it to cant over a little in the bore.

From memory the combustion chamber throat on a Coventry Victor opens out into the cylinder just above centre, between the two valves, and into a shallow trough shaped recess in the piston crown, so the single piece of lead wire won't give you a reading between the flat part of the piston crown and the head unless you poke it in another couple of inches or so, until it contacts the cylinder wall opposite.

As you said you were waiting for gaskets, I'm assuming that you were having the heads off anyway, so I'm at a loss to understand why you would want to use the single piece of wire method instead of the two identical sized pieces on the piston crown at right angles to the gudgeon pin, and then averaging the two readings after one turn over TDC.

Edited by Tony Dunkley
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Hi , Yes heads are off & valves have been out. I haven't decided that a single length of wire is the best way . Just the method put forward in the workshop manual. The shims for the bump clearance are sandwiched between the base of the barrels and the crankcase so once the heads are torqued down they won't need to be disturbed again , maybe this is why it is the Coventry victor preferred method.

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Hi , Yes heads are off & valves have been out. I haven't decided that a single length of wire is the best way . Just the method put forward in the workshop manual. The shims for the bump clearance are sandwiched between the base of the barrels and the crankcase so once the heads are torqued down they won't need to be disturbed again , maybe this is why it is the Coventry victor preferred method.

 

Sounds like you may have the air cooled version, . . . I was working on the assumption it was the water cooled version for some reason.

For engines with the bumping clearance shims under the barrels [air cooled Petters were the same, but Listers use shims under the heads instead] you can save yourself the work and time of pulling the barrels off the pistons again when checking the bumping clearance by putting all the shims that come with the gasket set under the barrels, taking the b.c. with the lead, and then taking out the required thickness of shims by easing the barrel up [with the piston at TDC] enough to cut the surplus shims with tinsnips and pulling them out.

Whichever engine you've got, air or watercooled, you can use this method for either one.

Edited by Tony Dunkley
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The engine is the water cooled marine , the heads have a self contained cooling jacket separate from the crankcase so the method of cutting out unwanted shims would work , or I could remove the head / barrel as an assembly and alter the amount of shims that way . In any case time is not an issue to me on this and i'll go with what is considered to be best practice on this thread and use more than one point on the piston crown to get a more accurate reading . If I had all the best answers I wouldn't be asking the questions. Thanks again for all the input / suggestions on this.

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The engine is the water cooled marine , the heads have a self contained cooling jacket separate from the crankcase so the method of cutting out unwanted shims would work , or I could remove the head / barrel as an assembly and alter the amount of shims that way . In any case time is not an issue to me on this and i'll go with what is considered to be best practice on this thread and use more than one point on the piston crown to get a more accurate reading . If I had all the best answers I wouldn't be asking the questions. Thanks again for all the input / suggestions on this.

 

I would think the head and barrel together might be a bit more cumbersome and awkward to fit back on over the piston and rings because of having to work horizontally instead of lowering them on vertically, . . . might increase the chances of breaking a ring.

At the risk of stating the obvious, leave out the pushrods and push rod tubes when fitting the heads with the lead strips on the piston crowns, . . it saves unnecessary faffing about with them twice.

 

Just out of interest, what's the box on your engine ? They fitted quite a variety of different makes to Coventry Victors, Enfields and Cubs, the best were Parsons or Joe's [American], and worst of all the Langdon and Fraser [southampton based comedians masquerading as engineers]. I do hope you haven't got one of them, . . . those responsible for designing and producing them should have been put up against a wall and shot.

Edited by Tony Dunkley
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Ok , Thanks for that. I couldn't find a matching gearbox when I fitted the engine in the boat so it's coupled to a Hurth box . More recently I found another marine HDW ( Mk 1 I think ) on a frame coupled to a heavy item of a box with no plate but I've been advised by 'Suigeneris' that it might have been made by a company called BRB. Would be great in a narrowboat but maybe too heavy for my small boat. Hope to get that up and running sometime this year.

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Ok , Thanks for that. I couldn't find a matching gearbox when I fitted the engine in the boat so it's coupled to a Hurth box . More recently I found another marine HDW ( Mk 1 I think ) on a frame coupled to a heavy item of a box with no plate but I've been advised by 'Suigeneris' that it might have been made by a company called BRB. Would be great in a narrowboat but maybe too heavy for my small boat. Hope to get that up and running sometime this year.

 

I'm glad to hear you haven't got a Langdon box.

I think BRB were one of the several companies that have made the TMP oil operated box, which was originally a Meadows design and the manufacturing rights were sold on several times. The TMP box was a bit unusual for an oil operated box in that ahead and astern operation was via cone clutches with the astern planetaries carried on one of the clutch cones, . . . similar internal layout to the Bruntons manual boxes that were fitted to Nationals and RN's in the 1930's. Unlike other oil operated boxes, TMP's didn't need a separate oil cooler because they had a watercooling jacket incorporated into the main casing.

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That's all good to know. It does look like a heavy duty piece of kit and would be good to fit it in a boat some time, just non availability of spare parts that would put me off running it, if anything wore out and needed replacing.

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  • 2 months later...

Finally got this boat back in Derwent and at weekend and had a good four hour run up to Elvington against flow. Really pleased with how she performs. The only thing which is perplexing me is a 'shushing' noise which sounds like escaping pressure. As a trial I used decompressor to stop engine and the noise continues until it comes to a stop. I hoped a good run might clear this but it's still there. Have heard that a broken ring can create noise but i'm sure that they are all intact. Could an injector create this noise ? It is in time with the engine speed. Everything else fine ,good power ,no smoke ,running cool. Any suggestions ? Thanks , Kieron.

Just thought that it can't be an injector because the noise continues after fuel is shut off at pump.

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I can't imagine the operation of an injector causing such noise, however if it's the seating of the injector into the head then it could be. Turning the pump off doesn't stop the pistons immediately so compressed air could be escaping past the injector nozzle during run down.

 

However I'd expect to be seeing exhaust smoke from that direction too.

Could it be a badly seated exhaust valve?

 

Why are you sure the rings are intact?

The rings might not be staggered.

You might have a stuck ring.

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I've just had heads and barrels off and checked rings out including position of gaps. Was thinking that stopping engine with decompressor would discount escaping compression. I have though poured a bit of diesel into the gap between injector and head and it doesn't get blown out so the injectors must be seated ok. Spent some time on grinding valves and was confident that they were good. I have got a diesel compression tester for the Landrover but not the right adaptor to fit this engine, but like I said it seems to be running fine. It has developed this new noise since I had it apart though. Thanks for suggestions.

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Hi Tony, It's more pulsating and in time with crankshaft rotation , it doesn't change note and is only noticeable at lower engine speeds I think because the volume of the engine over rides it at higher speeds. I'm just off to work now but will catch up with any new posts first thing (if there are any). thanks in advance.

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Hi Tony, It's more pulsating and in time with crankshaft rotation , it doesn't change note and is only noticeable at lower engine speeds I think because the volume of the engine over rides it at higher speeds. I'm just off to work now but will catch up with any new posts first thing (if there are any). thanks in advance.

Listening stick.

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Hi Tony, It's more pulsating and in time with crankshaft rotation , it doesn't change note and is only noticeable at lower engine speeds I think because the volume of the engine over rides it at higher speeds. I'm just off to work now but will catch up with any new posts first thing (if there are any). thanks in advance.

 

If you've got new rings in freshly honed/glaze-busted bores they can make a surprisingly loud sort of zizzy, scuffing noise until they've run for a few hours, . . . . not really loud enough to be heard when the engine is firing, but loud enough to hear perhaps on the over-run, or if you stop it decompressed.

 

It's difficult to be sure without actually hearing it running, but my best guess would be that it's air passing rapidly in and out of the crankcase breather. Both pistons move in and out together on the Coventry Victor twins [both cylinders at TDC and BDC at the same time] and an engine in good nick, with minimal piston/ring blow-by, will 'pant' in and out through the breather at the same frequency as crankshaft rpm, but more loudly and noticeably than a well-worn one with lots of blow-by and crankcase pressure

Edited by Tony Dunkley
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Thanks for that , will have a good look and listen 'Das boot' style with a stick when i'm there next. It's doesn't seem to affect the starting & running of the engine . I'll put it down to ' character '.

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Thanks for that , will have a good look and listen 'Das boot' style with a stick when i'm there next. It's doesn't seem to affect the starting & running of the engine . I'll put it down to ' character '.

Don't go off yer head and go berserk though or you might get shot by the Hauptmann.

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  • 3 weeks later...

Just to conclude this thread . Tony was 'on the money' with the diagnosis of crank case pressure causing this noise. Just by cranking the engine over with the oil filler cap removed the noise is gone. when I installed the engine I ran a 6ft small diameter breather pipe to the stern of the boat which is causing back pressure in the crankcase. If I reduce the length of this pipe to just outside the engine bay and increase the diameter I think all will be ok. The engine is obviously creating more crankcase pressure since being stripped down for some reason. Not blow by because the effect is the same when decompressed. It seems to be running well with the repitched prop. Might be a bit too fast at tickover for some sections of canal now though. Any way thanks for help on this.

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