Had my crm ar for 10 years! Never missed a beat until now!

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knackeredMk1
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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by knackeredMk1 » 02 Feb 2021, 20:26

If the piston has no marks/writing on the top then it is almost certainly on the original bore which will be 66.4mm. Is there a lot of 'blowby' on the piston? Brown/black extending below the piston rings. There may also be wear on the cylinder which will need to be measured with a bore gauge.

If so the cheapest option would be to rehone the bore and get a new set of rings for the 66.4mm bore - that might last for a while. BUT you are delaying the inevitable and in all probability you have a worn piston - After all it's a 30 year old bike!

LT will be able to measure everything properly and tell you what is needed.

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Gammakeith
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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Gammakeith » 03 Feb 2021, 09:01

It does seem terribly painful to rebore just because pistons are no longer available. I doubt the nikasil will be worn as its extremely tough. Any damage to the coating should be easily visible. Personally, I would carefully check the piston and if good then reuse with new rings/small end. That's what I did on mine. I used a second hand good barrel and piston and it transformed the bike (and done 2,000 miles since). That said, I am comfortable stripping engines and am aware I am taking a bit of a risk. After all, these are now classic bikes and if you are only using it hard for a handful of days each year then you should be fine for a good few years. Another option is the Chinese AR pistons advertised on ebay. Has anyone used one? I was tempted to try one myself but decided to play safe with an old Honda piston instead.

Keith

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Crmsam
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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 08 Feb 2021, 11:55

Thanks both for the guidence! I magaged to find a wosner 66.4 piston from pj motorcycle engineers in Wolverhampton who where extremely helpful!!! I got a top set of gaskets and a small end bearing (gen Honda) piston, g pin and C clips so good to go on the rebuild! I've lightly honed the bore striped and cleaned the power valve that was a right mess and took me ages! Also cleaned up the surfaces with some fine sand paper and a flat bench ready for new gaskets! Will update soon!
Thanks again all!

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Gammakeith » 09 Feb 2021, 08:14

Excellent. You are, however, still left with the mystery of why it seized (is that what happened?). It is important that you check oil pump/lines etc and rule out air leaks. Ideally, get a leak down test done on the engine when its reassembled.

Keith

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 20 Feb 2021, 09:06

Thanks Keith I don't have the kit or knowledge to do that level of test! How would you fellas suggest checking the oil pump without running the engine? I think the main problem was the inoperative power valve messing with mixture? As the bike was oiling fine before hand?

Update new piston, base gasket, small end and pin in place! (one pin circlip decided to jump out into my garage somewhere, as it leapt I was silent hoping to hear it fall nothing!!!! I found it balancing on my sons beta minitrials rear trye!)

I've hit a problem with the new head gasket and will try and explain!: the gasket matches perfectly apart from the front stud hole does not fit flush over the flange of the front stud the old gasket has an enlarged hole to cater for the flange! My options are try and open up the hole a little I could practice on the old gasket I have a pillar drill so I think I should be able to do this! Or source a new gasket? Thoughts?

Kind regards sam

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knackeredMk1
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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by knackeredMk1 » 20 Feb 2021, 11:03

Sounds like the new gasket is for the Mk1-3 CRM. The AR is slightly different. I suspect that using a pillar drill straight will distort or tear the gasket. I suggest you sandwich the gasket between two sheets of steel or aluminium ~3mm thickness and clamp it together - maybe even clamp it using several bolts??

Otherwise you could grind it out using a small grinding stone on a Dremel or similar tool - This might be the better way as it definitely won't distort the shape of the gasket. Just needs a steady hand.

You can check whether the oil pump is working by running the bike with premix in the tank and disconnecting the oil fed pipe from the inlet just before the engine and collecting the oil flowing through in a small bottle. You need to temporarily block the exposed pipe that the oil feed was connected to.

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 20 Feb 2021, 11:19

Thanks didn't think about grinding! Also I have some punches I could practice on the old gasket see which method works better!

Thanks again guys!

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 20 Feb 2021, 11:49

Also premix in the tank why didn't I think of that!!?

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Gammakeith » 20 Feb 2021, 15:10

Yep, that's good advice to follow re premix. Another way to check the pump is to introduce a small air bubble and watch its progress though that needs a clear oil line - You can even calculate the ml/min from the speed of the bubble as all you need to know is the internal diameter of the pipe. Crudely, you can also let the bike tick over and manually hold the oil pump wide open. You will soon find out if its working when it starts belching smoke out :-) To be frank, oil pumps are pretty bullet proof unless they have been messed with or have a leak.

Keith

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 21 Feb 2021, 18:50

So had success with the head gasket grinded out The front stud hole to the old gaskets diameter and gently cleaned up the burrs with a porting file! All back in and head on compression test from 60psi to 160! Really pleased with that!! Stripped off the rad to give them a good flush out, managed to acquire some new blue hoses. Which go with the bike nicely and put Everything back the way it was! (I just can't stop playing with the totally free power valve it's an addictive noise!)
Should be in a position to try for a start mid week ish! Thanks all for your help and guidence has helped me out loads!
Kind refars sam

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Crmsam » 26 Mar 2021, 10:34

Hi all took me a little longer to get round to start up basically gave everything a dam good clean up while it was all off the bike as well as checking and cleaning all the electrical connections, found a couple that were corroded! Built everything back up! (glad I took a load of pictures of how everything was routed!) did a final check before the moment of truth! Second kick and she fired up few coughs and splutters but is now running fine! Gentle ride round the block and the power is well and trulely back! Thanks all she live on!!

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by MaxCRM » 09 Feb 2022, 20:21

Hi all, jumping in on this thread if i may...

My CRM AR had been faultless for years, but has become hard to start. It tries to start after initial 2-3 kicks, runs for a couple of secs, wont really rev and then cuts out.

Spark is good
I've tried easy start - can't get it to fire on that
Stripped and cleaned carb - all clean in there, so no joy

I did a compression test and it read very slightly over 110PSI. From reading the thread above, that is low, but not horrendous - right?

I had the had the pipe off and looked at the piston - very slightest of a score mark on there. Can't seem to feel it with my finger nail though.

Does this sound about right, just enough compression to fire, but not enough to run properly?

What else should i check before removing the head/barrel?

I have read about about PVs - how can these be checked and cleaned?

Any thoughts appreciated.

Thanks in advance.
Max

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by MaxCRM » 09 Feb 2022, 20:33

Actually i lied... feeling again, i can feel the score mark with my nail. I guess that'll do it, right?

https://photos.app.goo.gl/MjDFTb7vsDDghuFu9

https://photos.app.goo.gl/c5vCKynDQ3rasqCE8

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777amia
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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by 777amia » 11 Feb 2022, 16:51

Should still run and rev with 110 psi. Was the test done with the throttle fully open?
How does it not rev? Bogging?
The score doesn't look too bad, I've had bikes which looks far worse up there and run half decent. What's the rings look like further up the piston?
Might be worth checking vacuum pipes as one is for idle control. The valve looks clean to me, remove cables and check its free moving, which I think it will be looking at it.

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Re: Had my crm ar for 10 years! Never missed a beat until now!

Post by Gammakeith » 13 Feb 2022, 08:41

My AR was a complete pain to start with a scored bore and worn rings. It ran fine once running though. A good bore and new rings transformed the starting. 110 psi is too low (though as always it depends on the accuracy of your gauge). That score is not too bad so worn (or stuck) rings are more likely to cause the low compression.

Keith


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