Author Topic: Engine misses and loses power  (Read 2002 times)

Online RDfella

  • Wise & Enlightened
  • *
  • Join Date: Aug 2017
  • Posts: 1051
  • Karma: 9
Re: Engine misses and loses power
« Reply #75 on: 14.03. 2020 20:14 »
Feel for you BJ. Had a similar experience several months ago, only with an unsolvable oiling issue. I was literally ready to smash up the (recently restored) bike with a lump hammer. I've actually no idea what stopped me, apart from realising it would be a waste of good material someone else probably needed. I then thought of parting it out - again a shame - but decided against after considering the hassle / postage etc involved. So I parked it out of sight at the rear of one of my sheds. Retuning to it some months later, out of curiosity I started it and the oiling issue had resolved itself. How? Why? These bikes have the best handling frame I've ever ridden, a pleasant engine and, in my view at least, are probably the best looking bikes ever made. But boy do they have foibles and can they be irritating!
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online BigJim

  • Valued Contributor
  • ****
  • Join Date: Aug 2018
  • Posts: 353
  • Karma: 1
  • Bristol. UK
Re: Engine misses and loses power
« Reply #76 on: 14.03. 2020 21:52 »
I remember your distress well RD. Hope that oiling issue has really gone away. It's that good money after bad that does it for me. Most of my expenditure is based on logic and reason, This seems to disappear when it comes to the BSA. Being unskilled and untooled as an engineer also means i have to take on trust the work of others.
To update this post , have managed 80 miles of motorway and A road use today. Bike has run well and .the whistle/whine seems less. As far as i can tell at the moment the recommissioned head had too tightly fitting valves which stuck open when engine was held at a steady 55ish. Have bought a reamer which i will be seeking advice on how to use.
Is this a hand drill or motor job. Basically whats the technique, what is the correct size, any obvious things to avoid doing?
Jamie,  Supporter of Distinguished Gentleman's Ride

Online Billybream

  • Resident Legend
  • *****
  • Join Date: Jan 2012
  • Posts: 529
  • Karma: 6
Re: Engine misses and loses power
« Reply #77 on: 15.03. 2020 04:25 »
Would be best to compare the clearance of a good valve and guide, you are looking for a few thousands of an inch, not sure your of reamer type, take things steady, try a hand drill with some lubricant, don,t rush.
Swop the valves over, it may be the valve stem that's oversize or damaged before using the reamer.
1960 Super Rocket, owned since 1966, back on the road 2012 after being laid up for 29yrs.

Online berger

  • Wise & Enlightened
  • *
  • Join Date: Nov 2017
  • Posts: 1361
  • Karma: 7
  • keith.chesterfield uk 500sscafe.norbsa project
Re: Engine misses and loses power
« Reply #78 on: 15.03. 2020 11:48 »
jim the whistle or whine could be exhaust gases passing between pipe and head port, I had a bit of that a few years ago and found a bit of blow by sooty marks when I took the finned ring off, but another whistle I had was head gasket leak. chin up , plenty black & tans *beer*

Online chaterlea25

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 3378
  • Karma: 48
Re: Engine misses and loses power
« Reply #79 on: 15.03. 2020 13:34 »
Hi Jim,
The reamer I suggested to you is a hand reamer, Do not use a power tool to operate it!!!!
Use a tap wrench to wind it clockwise through the guides, keep turning clockwise as you pull it back out, DO NOT reverse it
Lube with  spme WD40

John
1961 Super Rocket
1963 RGS (ongoing)

Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8513
  • Karma: 112
  • Lithgow NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Engine misses and loses power
« Reply #80 on: 15.03. 2020 19:37 »
As John said ^^^ and only 1,1/2 to 2 thou".
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online berger

  • Wise & Enlightened
  • *
  • Join Date: Nov 2017
  • Posts: 1361
  • Karma: 7
  • keith.chesterfield uk 500sscafe.norbsa project
Re: Engine misses and loses power
« Reply #81 on: 18.03. 2020 10:53 »
hi jim I have just read an article in classic bike where a valve was sticking and apparently it was proven a petrol tank sealing compound was causing this to happen, it is in ricks fixes march issue, just a thought if you have a tank sealing compound *beer*

Online BigJim

  • Valued Contributor
  • ****
  • Join Date: Aug 2018
  • Posts: 353
  • Karma: 1
  • Bristol. UK
Re: Engine misses and loses power
« Reply #82 on: 21.03. 2020 10:07 »
Thanks for all the advice and encouragement. I do have a tank sealing compound and am glad to have another thing to worry about.  *roll*
Just want to nail this topic down with regards to my input.  *bash*
Fitted a replacement head and had issues as discussed previously. Have refitted original and engine runs as before without missing or losing power.  *dunno2*
To conclude i am confident the head and work to it were the problem and will start a new post on head/guide/spending at some point in the future. *bright idea*
On a lighter note, foibles (as RD says) is certainly a trait for these bikes. With all the on and off of head and rockerbox the carb has been much disturbed. Being of the this won't take long (?) mentality i tend to strap it casually to the frame to keep it out of the way rather than strip the cables etc. This has changed it's attitude to starting. I now need to engage the choke to start up. Had not used the choke from when i replaced the carb to cure the loose slipring (happy days indeed). Please post suggestions for causes in a separate space as i am wandering way off topic!
Right i'm off out to see if i still have that nice whistle coming from the rockers.  *pull hair out*
Big thanks to all the input and even more for the encouragement. The big hammer and grinder are currently being kept out of sight, mind you, lets see how todays ride out goes.  *countdown* *beer* *wave* *bash* *thanks*
Jamie,  Supporter of Distinguished Gentleman's Ride