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  1. #21
    Rods 'n' Sods Junkie TheWebDesignCompany's Avatar
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    Quote Originally Posted by cptpugwash View Post
    Think this may be worth a first port of call
    I know that he used the pushrods from my old engine, but he said they were already hardened pushrods and the lash was adjusted and they were fine...?

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  3. #22
    Full Bloody Rebel! Mad Mark's Avatar
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    Have you checked the compression? Might be worth a look, then get to the timing? Is the cam dialled in properly? One tooth out can cause major problems.........
    If I wasn't meant to go that fast, the pedal would only go half way!

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    Rods 'n' Sods Junkie TheWebDesignCompany's Avatar
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    I paid to have that all done, (not checking the compression)

    These are the forged pistons I've got, they are supposed to have 10:1 compression





    I looked up and 68cc from 64cc should at most only lower the compression by half a point, and factoring in the larger flow numbers of the new race heads and the bigger valves that should more than make up for it shouldn't it?


    Ive gone from tyre shredding (even with apparently having 2 lobes wiped out on my cam) to got no power for pull away or even when you put your foot down.

    I have the double timing chain on the front and I took a photo when they were dealing in the cam.
    Last edited by TheWebDesignCompany; 13-10-2017 at 08:02.

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    Rods 'n' Sods Junkie TheWebDesignCompany's Avatar
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    You can see the double timing chain and the tool he used to dial in the camshaft...

  7. #25
    Official RnS Addict ivanhoew's Avatar
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    maybe , find the front pulley and put a bab of pint in the tdc mark ,find the pointer and dab of white paint , then fire it up ,with the vacuum advance pipe pulled off the distributor ,and put the timing light pickup on no1 ht lead , or the coil lead ,and see how the marks look at tickover and at half max rpm ,so around 3000 rpm .

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    Bicester scramble ,Medusa enjoyed the trip.https://www.youtube.com/watch?v=Q-7I7-nA19U

  8. #26
    Official RnS Addict 35kid's Avatar
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    your pistons will give you the below compression ratios depending on the CC of the heads - these numbers are direct from the TRW catalogue for your pistons.

    58cc heads - 11.26
    64cc heads - 10.5
    68cc heads - 10.02
    72cc heads - 9.59
    76cc heads - 9.19

    So you've went from a 68cc head which would give you a compression ratio of about 10.5 to a 74cc head which would give you a ratio of about 9.3
    Last edited by 35kid; 13-10-2017 at 09:17.

  9. #27
    Official RnS Addict 35kid's Avatar
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    Quote Originally Posted by TheWebDesignCompany View Post
    I paid to have that all done, (not checking the compression)

    These are the forged pistons I've got, they are supposed to have 10:1 compression


    I looked up and 68cc from 64cc should at most only lower the compression by half a point, and factoring in the larger flow numbers of the new race heads and the bigger valves that should more than make up for it shouldn't it?


    Ive gone from tyre shredding (even with apparently having 2 lobes wiped out on my cam) to got no power for pull away or even when you put your foot down.

    I have the double timing chain on the front and I took a photo when they were dealing in the cam.
    more flow is not always better unless you have matched parts - big intake runners will make less power than small ones if matched with the wrong manifold, carb and cam. A timing chain makes no difference at all to power. Did you get the old parts back from your mechanic? how do you know you had 2 wiped out lobes?
    Last edited by 35kid; 13-10-2017 at 09:22.

  10. #28
    Official RnS Addict 35kid's Avatar
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    Quote Originally Posted by draguar View Post
    If the new heads a lot larger size it could lower compression and reduce power? Or You said about lifters but did he replace the push rods as some aluminium heads require longer ones so your valves might not be opening properly? Just a guess I’m sure someone will be along in a min to tell me I’m talking ****! Lol


    Sent from my iPhone using Tapatalk
    different length pushords aren't about opening valves more, its more around where it puts the rocker in relation to the top of the valve. if your pushrod is too short you would find the rocker sits on the back of the valve stem not in the centre of it. likewise if its too long the rocker will sit at the front of the valve stem not in the centre.

    see diagram below to show what I mean - with the correct length pushrod the rocker should be in position 2 - too short and the end of the rocker sits at position 1, too long and the end of the rocker sits in position 3.

    Last edited by 35kid; 13-10-2017 at 09:39.

  11. #29
    Rods 'n' Sods Junkie TheWebDesignCompany's Avatar
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    Quote Originally Posted by 35kid View Post
    your pistons will give you the below compression ratios depending on the CC of the heads - these numbers are direct from the TRW catalogue for your pistons.

    58cc heads - 11.26
    64cc heads - 10.5
    68cc heads - 10.02
    72cc heads - 9.59
    76cc heads - 9.19

    So you've went from a 68cc head which would give you a compression ratio of about 10.5 to a 74cc head which would give you a ratio of about 9.3

    No I think I went from 64cc chamber heads to 68cc chamber heads which should only be a very minimal difference according to your chart. 10.5 down to 10.2
    Last edited by TheWebDesignCompany; 13-10-2017 at 10:01.

  12. #30
    Rods 'n' Sods Junkie TheWebDesignCompany's Avatar
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    Quote Originally Posted by 35kid View Post
    more flow is not always better unless you have matched parts - big intake runners will make less power than small ones if matched with the wrong manifold, carb and cam. A timing chain makes no difference at all to power. Did you get the old parts back from your mechanic? how do you know you had 2 wiped out lobes?

    Yes I insisted on having the old parts back, the lifters didnt look crushed at all the way he described it on the phone but 2 of then did have a noticeable curve worn out of the top.
    The cam shaft lobes were worn down on 2 of the lobes compare with the others.

    The carb is a summit racing 650 4 barrel carb, I'm not sure about the manifold, I know it was a performance one...

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