New problem unholy noise M750

jerry · 08-06-2020, 05:51 PM

The crashed M750 restoration is becoming a pain a couple of weeks ago I started the engine and all was well apart from rear cyclinder oil leak and no tickover on rear carb ,

So i tore it down cleaned the carb ther was a little dirt in Slow running jet lifted rear head and changed big O ring and little Oring on dowel ,, put some new belts on too and bolted it all back together ,, timing fine engine turns over with no plugs no interference ,, started engine and there is an unholy mechanical racket but nothing interfering ,, nothing loose or out of tolerance ,, so i suspect exhaust gaskets ,, cleaned out the exhaust ports thoroghly so the have no gaskets or debris fit new ducati early thin type ex gaskets and start bike still unholy noise and poor running ???im convinced its the exhaust gaskets I have fitted the latter type thick ones which make it even worse ,,

im getting paranoid because i thought the valves were hitting piston but cant be that

either im missing something but have 3 750s never seen an issue like this before ???

I think that ducati are not supplying me the correct parts as the original gaskets were fibre and all the ones they are sending are mettallic even the thin ones and they also seem a little small for the post in diameter

im completely baffled also the left hand cab is still not working on slow circuit ???unles this is a symptom all the igniters , coils , plugs leads are working fine tested them on other bike ans fuel is flowing on main jets ?

jerry · 10-06-2020, 07:54 PM

OK progress but not good news removed heads rear head ,valves and piston all perfect but front ,,no damage to bore or piston ,,, inlet valve is fine ,, opener rockers and cam all ok as are head bearings ,

the exhaust valve is the problem head exhaust valve partially seized??? i have it out now the fork on the closing rocker may be bent have to compare to inlet closer fork ,, the valve stem is smooth and unmarked inside , the valve neck is straight when placed on a flat glass and the valve poppet has no damage ??

so what to do hmmm???

utopia · 10-06-2020, 10:03 PM

What is the recent history of this engine, Jerry ?
Has any work been done on it since the crash ?
If so, can you give a link to the appropriate thread.

jerry · 11-06-2020, 09:00 AM

I know how it happened when I was undoing the cam nuts the engine slipped a bit and the front cam turned must have interfered somewhere it was maybe a 1/4 turn ,,this is the first time in 16 years the front head has been off ,, Im certain the actual closer rocker fork is slightly bent ,, the valve itself seems straight and the guide seems fine ,, its weird ,, the rear head is fine as is crank pistons etc ,,

thing is should I get new valve and guide and rocker or what ???

jerry · 11-06-2020, 09:02 AM

Im going to have to buy a rocker spring tool anyway looking for cheapest deal

jerry · 11-06-2020, 06:10 PM

Ok took the heads to my local specialist engine rebuilders and machine shop ,, he checked the valves and guides thoroughly measured everything he states that the ex valve is not bent and the guide is in spec ,, also the forked rocker is clearing ,, so whatever was binding it up is now free.??? he checked all over so im going to reassemble the head and see whats what ?????

Mr Gazza · 11-06-2020, 07:06 PM

Is it getting the proper oil supply?

jerry · 11-06-2020, 07:29 PM

Quote:

Originally Posted by Mr Gazza

Is it getting the proper oil supply?

yes head full of oil all bearings fine ,,

Dukedesmo · 11-06-2020, 10:43 PM

Is the inside of the valve guide 'bruised'?

My Son's car broke the cambelt last year and all the exhaust valves were bent (intakes were fine).

I fitted all new valves but 2 of the guides were tight due to the valve having been 'rocked' in there, ran through with a reamer and they were fine.

For the few quid a reamer costs, it'd be worth doing IMHO.

jerry · 12-06-2020, 03:48 PM

Quote:

Originally Posted by Dukedesmo

Is the inside of the valve guide 'bruised'?

My Son's car broke the cambelt last year and all the exhaust valves were bent (intakes were fine).

I fitted all new valves but 2 of the guides were tight due to the valve having been 'rocked' in there, ran through with a reamer and they were fine.

For the few quid a reamer costs, it'd be worth doing IMHO.

No bruising its all fine and in spec ,, im going to reassemble and see how it turns over on the bench if its easy and smooth I will fit head to bike and start it ,, but if it binds or ex valve sticks the I will have to investigate but my local engine rebuilding shop says its OK .

jerry · 13-06-2020, 03:33 PM

Front head reassembled all valve shims checked again and in spec ,, but when turned over the exhaust valve is very very tight and I can see some marks on the valve stem where it is touching the closer fork ,, im going to drop the head off with Alf and see what he says he is a ducati specialist used to work with JPS race bikes ?????? somethin bent on the exhaust side for sure

utopia · 13-06-2020, 03:42 PM

I think I'd be inclined to double check that the exhaust valve is straight by lightly lapping the valve seat and then checking to see whether you get an even, grey colour all round ... ie full contact.

manwithredbike · 13-06-2020, 04:19 PM

How does the valve feel in the guide on its own with the cam gear disconnected, is it moving freely and smoothly? as Utopia says, i'd check the valve head was seating properly in the port. I once bent a valve in my M900. The stem was straight as a die but the head was just slightly bent off square, caused by moving an engine when the belts were off. (When you say you moved the engine, did it turn with the belts off too?) If so, you'd end up damaging the cam and the closer (as i did by turning it over) and possibly the shim as the closer gap could go below zero. If that makes sense.

jerry · 14-06-2020, 08:10 PM

The valve was lightly lapped and a vaopur test was performed ,, it moves easy in the guide , im going to engineers blue the valve stem and see what marks appear when all the rockers are assembled

Dukedesmo · 14-06-2020, 11:29 PM

If the valve is straight, clean and a good, central fit in the guide and seat then you should be able to 'bounce' it as you flick it into the head.

08-06-2020, 05:51 PM	#1
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	New problem unholy noise M750 The crashed M750 restoration is becoming a pain a couple of weeks ago I started the engine and all was well apart from rear cyclinder oil leak and no tickover on rear carb , So i tore it down cleaned the carb ther was a little dirt in Slow running jet lifted rear head and changed big O ring and little Oring on dowel ,, put some new belts on too and bolted it all back together ,, timing fine engine turns over with no plugs no interference ,, started engine and there is an unholy mechanical racket but nothing interfering ,, nothing loose or out of tolerance ,, so i suspect exhaust gaskets ,, cleaned out the exhaust ports thoroghly so the have no gaskets or debris fit new ducati early thin type ex gaskets and start bike still unholy noise and poor running ???im convinced its the exhaust gaskets I have fitted the latter type thick ones which make it even worse ,, im getting paranoid because i thought the valves were hitting piston but cant be that either im missing something but have 3 750s never seen an issue like this before ??? I think that ducati are not supplying me the correct parts as the original gaskets were fibre and all the ones they are sending are mettallic even the thin ones and they also seem a little small for the post in diameter im completely baffled also the left hand cab is still not working on slow circuit ???unles this is a symptom all the igniters , coils , plugs leads are working fine tested them on other bike ans fuel is flowing on main jets ? __________________ MONSTERMAN

10-06-2020, 07:54 PM	#2
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	OK progress but not good news removed heads rear head ,valves and piston all perfect but front ,,no damage to bore or piston ,,, inlet valve is fine ,, opener rockers and cam all ok as are head bearings , the exhaust valve is the problem head exhaust valve partially seized??? i have it out now the fork on the closing rocker may be bent have to compare to inlet closer fork ,, the valve stem is smooth and unmarked inside , the valve neck is straight when placed on a flat glass and the valve poppet has no damage ?? so what to do hmmm??? __________________ MONSTERMAN

11-06-2020, 09:00 AM	#4
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	I know how it happened when I was undoing the cam nuts the engine slipped a bit and the front cam turned must have interfered somewhere it was maybe a 1/4 turn ,,this is the first time in 16 years the front head has been off ,, Im certain the actual closer rocker fork is slightly bent ,, the valve itself seems straight and the guide seems fine ,, its weird ,, the rear head is fine as is crank pistons etc ,, thing is should I get new valve and guide and rocker or what ??? __________________ MONSTERMAN

11-06-2020, 09:02 AM	#5
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	Im going to have to buy a rocker spring tool anyway looking for cheapest deal __________________ MONSTERMAN

11-06-2020, 06:10 PM	#6
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	Ok took the heads to my local specialist engine rebuilders and machine shop ,, he checked the valves and guides thoroughly measured everything he states that the ex valve is not bent and the guide is in spec ,, also the forked rocker is clearing ,, so whatever was binding it up is now free.??? he checked all over so im going to reassemble the head and see whats what ????? __________________ MONSTERMAN

10-06-2020, 10:03 PM	#3
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	What is the recent history of this engine, Jerry ? Has any work been done on it since the crash ? If so, can you give a link to the appropriate thread.

11-06-2020, 07:06 PM	#7
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,803	Is it getting the proper oil supply? __________________

11-06-2020, 10:43 PM	#9
Dukedesmo Registered User Join Date: Sep 2010 Location: Leics Bike: M900 Posts: 2,842	Is the inside of the valve guide 'bruised'? My Son's car broke the cambelt last year and all the exhaust valves were bent (intakes were fine). I fitted all new valves but 2 of the guides were tight due to the valve having been 'rocked' in there, ran through with a reamer and they were fine. For the few quid a reamer costs, it'd be worth doing IMHO. __________________ M900, 916, LeMans II.

13-06-2020, 03:33 PM	#11
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	Front head reassembled all valve shims checked again and in spec ,, but when turned over the exhaust valve is very very tight and I can see some marks on the valve stem where it is touching the closer fork ,, im going to drop the head off with Alf and see what he says he is a ducati specialist used to work with JPS race bikes ?????? somethin bent on the exhaust side for sure __________________ MONSTERMAN

13-06-2020, 03:42 PM	#12
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	I think I'd be inclined to double check that the exhaust valve is straight by lightly lapping the valve seat and then checking to see whether you get an even, grey colour all round ... ie full contact.

13-06-2020, 04:19 PM	#13
manwithredbike aka Phil Join Date: Nov 2005 Location: derry Bike: M900 Posts: 376	How does the valve feel in the guide on its own with the cam gear disconnected, is it moving freely and smoothly? as Utopia says, i'd check the valve head was seating properly in the port. I once bent a valve in my M900. The stem was straight as a die but the head was just slightly bent off square, caused by moving an engine when the belts were off. (When you say you moved the engine, did it turn with the belts off too?) If so, you'd end up damaging the cam and the closer (as i did by turning it over) and possibly the shim as the closer gap could go below zero. If that makes sense. __________________ .. ~

14-06-2020, 08:10 PM	#14
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	The valve was lightly lapped and a vaopur test was performed ,, it moves easy in the guide , im going to engineers blue the valve stem and see what marks appear when all the rockers are assembled __________________ MONSTERMAN

14-06-2020, 11:29 PM	#15
Dukedesmo Registered User Join Date: Sep 2010 Location: Leics Bike: M900 Posts: 2,842	If the valve is straight, clean and a good, central fit in the guide and seat then you should be able to 'bounce' it as you flick it into the head. __________________ M900, 916, LeMans II.