Series 2 what should be the compression test readings on a 2a petrol

peter8315 · Dec 8, 2015

just fitted my head back after unleaded conversion on it, and its running rough, seems like its missing on one cylinder plugs and leads are new, and if i disconnect the plug lead off cylinder 3 it doesn't alter anything, so did compression test and number three is showing 60psi, numbers one and two are 70, and number 4 is 80, are these about right, i would have thought number 3 was a tad low

chris7 · Dec 8, 2015

Peter they are ALL too low! mechanics use the rule of 90,anything below is too low! my series 3 has 165 on each cylinder after its rebuild slight difference between high and low compression engines 20psi l think! Have you torqued the head correctly and adjusted each valve?

peter8315 · Dec 8, 2015

wow, looks like head coming off again

jamesmartin · Dec 8, 2015

peter8315 said:
wow, looks like head coming off again

your not going to achieve much by removing head, cure lead /spark issue ensure tappets are 100% see how it runs,it might be poor tester or slow starter poorly set valves etc

peter8315 · Dec 8, 2015

Theres a good spark there James, i have checked tappet clearance twice today, i have a feeling that it might be a valve not seatig properly, as stated i have just had an unleaded on the exhaust valve seats and the machine shop was supposed to lap the new exhaust valves in to the new seats, i should have checked them before i fitted the head, a top tip from ed china on wheeler dealers is to tip head upside down and pour a drop of petrol in the dome, if it seeps out there is obviousley a bad seal

peter8315 · Dec 8, 2015

a little more info, number 3 plugs is showing signs of wettness, and other are dry

tottot · Dec 8, 2015

Peter,Are your measurements after just one piston stroke ?

peter8315 · Dec 8, 2015

is that for tappet clearance, i use the add up to 9 metthod.

peter8315 · Dec 9, 2015

found out what the compression readings should read today, and its around the 130psi thats on the low compression model, so it looks like heads coming off and lap all the valves in

Edlandy · Dec 9, 2015

... Before you do out drastic, are you sure your tester is ok, all plugs out and throttle fully open on a hot engine.... Does a little bit of oil improve readings much..... Sorry if you know all this already

jamesmartin · Dec 9, 2015

peter8315 said:
Theres a good spark there James, i have checked tappet clearance twice today, i have a feeling that it might be a valve not seatig properly, as stated i have just had an unleaded on the exhaust valve seats and the machine shop was supposed to lap the new exhaust valves in to the new seats, i should have checked them before i fitted the head, a top tip from ed china on wheeler dealers is to tip head upside down and pour a drop of petrol in the dome, if it seeps out there is obviousley a bad seal

if a valve is leaking you will hear it in the manifold,if you add a squirt or two of oil and restest it should show whether rings or valves

peter8315 said:
a little more info, number 3 plugs is showing signs of wettness, and other are dry

its the one not firing, id try and get that plug firing first

peter8315 · Dec 10, 2015

All plugs are firing, i bit the bullet today and whipped the head off, leak off tested negative parrafinn in combustion chambers never moved after 1 hour, so its not the head, checked pistons and hardly any side movement and must have had a rebore at some time as got +20 on piston crowns, no lip either at top of bore, so now i am stuffed, anybody got a good 21/4 peterol engine for sale?

jamesmartin · Dec 10, 2015

peter8315 said:
All plugs are firing, i bit the bullet today and whipped the head off, leak off tested negative parrafinn in combustion chambers never moved after 1 hour, so its not the head, checked pistons and hardly any side movement and must have had a rebore at some time as got +20 on piston crowns, no lip either at top of bore, so now i am stuffed, anybody got a good 21/4 peterol engine for sale?

it isnt firing if removing lead makes no difference, and its the only wet one,its that what you need to be looking for

divie · Dec 10, 2015

Did you fit/have fitted new valve guides ? I have had to ream exhaust guides in the past after fitting they where to tight. Even with a sticky valve the plug should not wet, swop the dizzy cap and try again. Oh also check the firing order.

peter8315 · Dec 10, 2015

the plug itself is firing, but when pulling that plug lead off it doesn't affect the rocking of the engine, i will try your metthod Jame's when i put the head back on with a squirt of oil down plug holes, this will show up if bores/rings are worn, but i can,t get over the low compression, perhaps it is my tester.

peter8315 · Dec 10, 2015

No Divie, didn't do them, but i would have thought that they would have nothing to do with the compression, as they are after the valve seat, ref the dizzy cap its the only thing i havn't changed, but will give it a go, just got to refit head back first, and got to order a head gasket

jamesmartin · Dec 10, 2015

are all valves fully opening ,are all adjusters equal

peter8315 · Dec 10, 2015

yes James, been through them 3 or4 times, it starts fine and runs lumpy and the exhaust note is like its missing on one cylinder, engines rocking, and now and again pops back through carb, it give the impression that its a plug down but they are all new and i have checked them for spark, i had to satisfy my own mind about the valve seats, at least i know that they are ok

tottot · Dec 11, 2015

You will only get a full compression after 4 to 6 revolutions of motor,around 70psi on first stroke is good for a series petrol.

Edlandy · Dec 11, 2015

Misfires and spitting back through the carb are normally due to timing problems, go through the lot and make sure everything is set right , everybody has put plugs leads on wrong at least once as well

Series 2 what should be the compression test readings on a 2a petrol

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