Compression on new motor R50

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charlton20

Compression on new motor R50

Postby charlton20 » Mon Nov 23, 2015 11:47 am

Hi from Australia. I have just had my R50 motor and gearbox rebuilt by a very highly respected BMW boxer engine specialist, I gave him a free hand to give me the best outcome. Although the compression was down before the reco job my main reason for the rebuild job was that the crank shaft was starting to move for and aft so I decided to do the whole job. I removed the motor from the frame removed all of the accessories and gave him the motor & g/box untouched. I must say that it was performing very well considering how worn it was when he dismantled it for inspection.
Some four weeks later it was ready so I went and picked it up parted with a lot of $$$ and went on my way, I installed the motor & g/box and hung on all of the external components necessary to return it to its former glory, then I tried to start it, it would back fire, it would flood, it would attempt to run on for about ten revolutions and stop. I kept at it and must have turned over the motor the equivalent of ten mile as the hour meter was recording all the time that the ignition was sparking and it clocked up a lot of time. In desperation I contacted the engine builder to as him if he knew of any one who had a set of rollers to roll start the bike, he volunteered that he had a set and I could come and use them and I did, we had to run the bike at about 15mph to get it to start and it would not remain running below 2000rpm. He took the rocker covers off and found that the rocker gear was fouling against some other part of which I am unsure what it was, he removed the rocker gear and ground away some of the webbing area and reassembled the rocker gear adjusted the tappets and put it back on the rollers and it lit up within moments, he made a few adjustments and it all appeared well, home I went. Prior to taking the whole bike back to him I did a compression test and it was reading 60psi on the LHS and 50psi on the RHS I told him this and he said that it would come good with use. I have now done 280 miles and a lot more hours of running time in my garage trying to get it to run properly, It starts with ease and will idle at 850 to 900 rpm when cold but when it is hot after about 5 miles I have to hold the throttle open when stoped or out of gear to keep it running, it is extremely frustrating as it was a better behaved motor before the rebuild. I have recently checked the compression again and it is still 60psi on the left and 51psi on the left. CAN ANYBODY out there tell me what PSI compression it should have had at original start up and what I could expect at 280 miles and how long it will take to grow to its maximum PSI ???
As part of my endeavour to fix my problems I have purchased two NEW Bing 1/24/146 & 145 carbies which have helped, I have a PowerDynamo ignition /12v alternator on the motor which was there 12 months before the rebuild and it has always been excelent.
A young guy who lives near by also had his motor rebuilt at the same time buy the same repairer, this job was a budget job, it has now done 650 miles and has 115 psi on both sides and runs superbly, I feel very let down.
FRANK from AUS.

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boxerman
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Re: Compression on new motor R50

Postby boxerman » Mon Nov 23, 2015 12:03 pm

I know little of the pre /5 machines but my first concern would be that he had to start grind parts that were OK before - to me that would suggest that something has been incorrectly assembled. As I say, I don't know the pre /5 machines but I'd have thought a good engine should be showing something like 140 - 150 psi - what you're seeing sound appalling for a newly rebuilt engine. Are you sure the guy knows what he's doing?

If a /5 onward bike was showing that kind of compression I'd be telling the customer that his top end was knackered and going to need good money spending to put right.
Phil Hawksley 'The Boxer Man' - aka 'Dangermouse'
Member #1 Much modified R80G/S - a REAL one
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charlton20

Re: Compression on new motor R50

Postby charlton20 » Mon Nov 23, 2015 12:12 pm

Hi Phil. This was a no $$$ spared rebuild, new all and every thing as per requirement. The motor when new was 6.8 to one which reflects about 125psi. Thanks. FRANK

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Galactic Greyhound
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Re: Compression on new motor R50

Postby Galactic Greyhound » Mon Nov 23, 2015 12:24 pm

Hi Frank,

Just in case......
When doing a compression test, the carburettors should be removed from the intake manifolds to ensure correct measurement.
Ced.

R1100RT 1996.
Sent by Boson Quantum Transmission from the Starship 'Galahad'.
http://www.researchgate.net/publication ... ing_bosons" - It works!

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bwprice100
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Re: Compression on new motor R50

Postby bwprice100 » Mon Nov 23, 2015 4:07 pm

If he is grinding the webs of the rockers that means they have been swapped around and the inlets from one side have been swapped with the exhausts on the other side and vica versa.
I would ask for your money back, any one expecting that much lost compress to be made up by running in is taking the p#*s.

I hope this helps Brian

www.ebolt.co.uk
1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
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Jaythro
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Re: Compression on new motor R50

Postby Jaythro » Mon Nov 23, 2015 5:51 pm

I would remove the heads and turn them upside down with rocker gear removed and a used spark plug inserted get them as level as possible and pour on a little kerosene and check the ports and see if one or both are leaking

If the valve clearances were correct I would suspect VERY Sloppy valve grinding

Nothing should need clearanced if its back together correctly!!

I would expect at least 120 ish psi from a refurbished rising as the motor beds in over the first 100 miles or so!!!
"Put your Ass on a motorcycle and ride with an attitude and the "Grim Reaper" will ride in your shadow!"

Islandmagee in case you're interested?

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Re: Compression on new motor R50

Postby boxerman » Mon Nov 23, 2015 10:43 pm

Having read Brian's suggestion (he does know the early bikes pretty well) and bearing in mind that the 'repairer' mentioned that the rockers were fouling something I can now see a likely scenario. Lack of care in storage meant that rockers were mixed up and wrongly fitted, rocker arms fouling something and jamming with valve partly open, pistons rise and smack the valves resulting in slightly bent and partially open valves under all conditions. Result - valves leaking badly and bent, possibly slight damage to pistons where they touched. Could well be wrong but it's a fair guess from what's been gleaned.

You need to get the bike back to the builder and insist he checks out what he's done.
Phil Hawksley 'The Boxer Man' - aka 'Dangermouse'
Member #1 Much modified R80G/S - a REAL one
Why not join the BM Riders Club @ http://www.bmridersclub.com
http://www.boxerman.co.uk
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https://twitter.com/boxermanphil for my Badger videos

charlton20

Re: Compression on new motor R50

Postby charlton20 » Wed Nov 25, 2015 11:05 am

Hi Gents. thank you for your responses. When I do the compression test I can leave the gage in place for a lengthy period of time and it does not loose any pressure until I release it and I feel that is heartening in a small way. With regard to doing the comp tests I remove the carby slide complete with the needle and also remove the external intake pipes and I feel that this frees up the air flow to as good as it gets.
Today the repairer phoned me and invited me to bring the bike back to him and he would try to establish what has gone wrong and then do what ever repairs are required to rectify my ailing motor, he is very fastidious and will only seek to deliver the best outcome so I am quietly confidant.
Thank you once again, I will report the outcome when we get to the other side. FRANK

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bwprice100
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Re: Compression on new motor R50

Postby bwprice100 » Wed Nov 25, 2015 11:41 am

Hi Gents. thank you for your responses. When I do the compression test I can leave the gage in place for a lengthy period of time and it does not loose any pressure until I release it and I feel that is heartening in a small way. With regard to doing the comp tests I remove the carby slide complete with the needle and also remove the external intake pipes and I feel that this frees up the air flow to as good as it gets.
Today the repairer phoned me and invited me to bring the bike back to him and he would try to establish what has gone wrong and then do what ever repairs are required to rectify my ailing motor, he is very fastidious and will only seek to deliver the best outcome so I am quietly confidant.
Thank you once again, I will report the outcome when we get to the other side. FRANK
That sounds promising Frank

Brian
1958 R26, (not so many bits now)
1978 R75/7, (a project bike)
1981 R80, (was a TIC)
1995 R1100RT, (speeding ticket the first day I rode it) (Sold)
http://www.eBolt.co.uk
http://www.ToolroomChucks.co.uk


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